UBC Theses and Dissertations

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UBC Theses and Dissertations

A Study of the spectra of some organic compounds Zwarich, Ronald James 1968

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A STUDY OF THE SPECTRA OF SOME ORGANIC COMPOUNDS  BY  RONALD JAMES ZWARICH B.Sc.  (Hons.) U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1963  A THESIS SUBMITTED' IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  i n t h e Department of CHEMISTRY  We accept t h i s  t h e s i s as c o n f o r m i n g t o t h e  required standard  The U n i v e r s i t y o f B r i t i s h December, 1968  Columbia  In  presenting  an  advanced  the I  Library  further  for  this degree shall  agree  scholarly  by  his  of  this  written  thesis  in p a r t i a l  f u l f i l m e n t of  at  University  of  the  make that  i t freely  permission  purposes  may  representatives. thesis  for  be It  financial  available for  by  the  is understood gain  Department Columbi  for  extensive  granted  permission.  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  British  shall  reference  Head  be  requirements  Columbia,  copying  that  not  the  of  and  of my  I agree  for that  Study.  this  thesis  Department  copying  or  allowed  without  or  publication my  Abstract The  fundamental v i b r a t i o n s o f c a r b a z o l e have been a s s i g n e d  p o l a r i z e d i n f r a r e d , Raman and f l u o r e s c e n c e s p e c t r a .  from  A crude normal  c o o r d i n a t e c a l c u l a t i o n u s i n g a f o r c e f i e l d t r a n s f e r r e d from phenanthrene for  the i n - p l a n e p r o b l e m , and from benzene and a n t h r a c e n e f o r the  out-of-plane  problem gave s a t i s f a c t o r y agreement w i t h the observed f r e q u e n c i e s .  From  a study o f the p o l a r i z e d a b s o r p t i o n spectrum o f c a r b a z o l e i n a s i n g l e c r y s t a l m a t r i x o f f l u o r e n e at about 15°K, i s assigned  ^A^-«—  a  n  c  the l o w e s t - e n e r g y  * the e x c i t e d s t a t e v i b r a t i o n s are  transition analysed. o  In f l u o r e n e , an i m p u r i t y w i t h a weak a b s o r p t i o n at 3200 A, w h i c h p r e v i o u s workers i n a d v e r t e n t l y a t t r i b u t e d t o f l u o r e n e i t s e l f , was i z e d as b e n z [ f ] i n d a n .  From t h e p o l a r i z e d a b s o r p t i o n and  s p e c t r a , the t r a n s i t i o n i s assigned t h e s e s p e c t r a are  *Aj-«—^^\>  a n c  character-  fluorescence  * v i b r a t i o n a l analyses  of  given.  From a study o f the a b s o r p t i o n spectrum o f a - f l u o r e n e  crystal  (ab f a c e ) ,  the s o l u t i o n a b s o r p t i o n spectrum i s g i v e n the f o l l o w i n g i n t e r p r e t a t i o n : o  o  the 3000 A system o f medium i n t e n s i t y and the s t r o n g e r 2600 A system are o  l o n g - a x i s p o l a r i z e d , and a r a t h e r weak band at 2730 A i s s h o r t - a x i s polarized.  V i b r a t i o n a l analyses  o f the a b s o r p t i o n and f l u o r e s c e n c e  i n a p o l y c r y s t a l l i n e n-heptane m a t r i x at about 15°K  are p r e s e n t e d .  v i b r a t i o n a l a n a l y s i s o f t h e i n t e n s e b l u e phosphorescence induced by the d e l i b e r a t e a d d i t i o n o f d i b e n z o t h i o p h e n e at about 6°K  spectra A  i n fluorene  shows t h a t the  i n t e r v a l s are i d e n t i c a l w i t h those i n t h e f l u o r e s c e n c e and phosphorescence o f f l u o r e n e i n n-heptane.  An assignment o f the fundamentals o f f l u o r e n e  from p o l a r i z e d i n f r a r e d and Raman s p e c t r a i s r e p o r t e d . P o l a r i z e d i n f r a r e d and Raman s p e c t r a o f d i b e n z o t h i o p h e n e - h  and  -d.  are  utilized  i n an assignment o f t h e i r fundamental v i b r a t i o n s . The  in-plane  f r e q u e n c i e s were c a l c u l a t e d u s i n g t h e f o r c e f i e l d t r a n s f e r r e d from phenanthrene. 15°K  The l o w e s t - e n e r g y t r a n s i t i o n o f dibenzothiophene i n f l u o r e n e a t about  i s assigned  * A j - * — .  V i b r a t i o n a l analyses  o f t h e a b s o r p t i o n spectrum  i n n-heptane and o f the f l u o r e s c e n c e and phosphorescence s p e c t r a i n the c r y s t a l , n-heptane, and hexamethylbenzene  are  presented.  An i n t e n s e b l u e phosphorescence o b s e r v e d at 6°K  i n a biphenyl  crystal  f o l l o w i n g t h e d e l i b e r a t e a d d i t i o n o f e i t h e r c a r b a z o l e or d i b e n z o t h i o p h e n e was i d e n t i f i e d as b i p h e n y l phosphorescence o r i g i n a t i n g from energy t r a p p i n g c e n t e r s c r e a t e d i n the c r y s t a l l a t t i c e .  The t r i p l e t band energy o f b i p h e n y l  e s t i m a t e d from p r e l i m i n a r y t e m p e r a t u r e dependence s t u d i e s o f t h e phosphorescence and d e l a y e d f l u o r e s c e n c e agrees s a t i s f a c t o r i l y w i t h H i r o t a ' s independent measurement.  - iv Table o f  Contents  Abstract  1 1  T a b l e o f Contents  i v  L i s t of Figures  l x  L i s t of Tables  x i v  Acknowledgements  Chapter  1  General I n t r o d u c t i o n  ....  xvm  •  1  A.  I n t r o d u c t o r y Remarks  1  B.  The Theory o f V i b r a t i o n a l - E l e c t r o n i c I n t e r a c t i o n s  3  C.  The  8  D.  The Theory o f E x c i t o n s i n M o l e c u l a r C r y s t a l s  E.  C o u p l i n g C r i t e r i a and D i s s i p a t i o n o f E x c i t a t i o n Energy  Franck-Condon P r i n c i p l e  9  i n Molecular Crystals  15  F.  Mixed M o l e c u l a r C r y s t a l Systems  17  G.  The Theory o f M o l e c u l a r V i b r a t i o n s  18  H.  The  24  I.  D e t e r m i n a t i o n o f Force C o n s t a n t s  Chapter  2  I n t e n s i t y o f I n f r a r e d Bands  M a t e r i a l s and E x p e r i m e n t a l Methods  25  28  A.  P u r i f i c a t i o n and S y n t h e s i s o f M a t e r i a l s  28  B.  P r e p a r a t i o n o f Samples  33  C.  Cryostats  3 4  D.  C a l i b r a t i o n o f Gas Thermometer  35  E.  Apparatus .;  3  ^  F.  Infrared Spectra  3  ^  G.  Raman S p e c t r a  3  ^  - v -  H.  Measurement o f S p e c t r a  I.  C r y s t a l Data and O p t i c a l P r o p e r t i e s o f Some O r g a n i c  4  Compounds Chapter  3  •  •  4  0  ^  A V i b r a t i o n a l Assignment o f C a r b a z o l e from I n f r a r e d , 48  Raman, and F l u o r e s c e n c e S p e c t r a A.  Introduction  48  B.  S e l e c t i o n Rules  49  C.  The I n f r a r e d Spectrum  D.  The Raman S p e c t r a  E.  The F l u o r e s c e n c e Spectrum  62  F.  Assignment o f Fundamentals  69  G.  Normal C o o r d i n a t e C a l c u l a t i o n  72  H.  Conclusion  ^9  Chapter  4  5 3  •  58  The A b s o r p t i o n Spectrum o f C a r b a z o l e i n a F l u o r e n e 82  Matrix A.  Introduction  82  B.  Spectrum  ^  C.  Discussion  Chapter  5  .  3  88  U l t r a - v i o l e t Spectra of Benz[f]indan Impurity i n a Fluorene C r y s t a l  92  A.  Introduction  92  B.  The Mixed C r y s t a l Systems  93  C.  The A b s o r p t i o n Spectrum  95  D.  The F l u o r e s c e n c e Spectrum  99  - vi -  E. Chapter  102  Discussion 6  A Study o f Some E x c i t e d S i n g l e t and T r i p l e t States o f Fluorene  Electronic ••  A.  Introduction  106  B.  The Pure C r y s t a l S p e c t r a  1 0 7  1.  S e l e c t i o n Rules  1  2.  C r y s t a l Energies  109  3.  Calculation of the Crystal S p l i t t i n g s ; Dipole-Dipole  C.  Chapter  0  7  Approximation  109  4.  Room Temperature A b s o r p t i o n  113  5.  A b s o r p t i o n a t Low Temperature  H6  6.  F l u o r e s c e n c e a t Low Temperature  H  7  Spectra i n a Matrix 1.  The A b s o r p t i o n Spectrum  120  2.  The F l u o r e s c e n c e Spectrum  122  3.  The T r i p l e t S t a t e  7  I  2  5  I  3  2  A V i b r a t i o n a l Assignment o f F l u o r e n e from t h e I n f r a r e d and Raman S p e c t r a  A.  Introduction  B.  S e l e c t i o n Rules  C.  The I n f r a r e d Spectrum  D.  Raman S p e c t r a /  E.  i  I  3  2  3  4  1^0 •  14^  Assignment o f Fundamentals 1.  The Low-Energy Region  i 4 5  2.  A  i  1  Symmetry  4  6  - vii -  F.  3.  B  4.  A 2 Symmetry  148  5.  B  148  1  2  Symmetry  :  .147  Symmetry  Discussion  Chapter 8  149  A V i b r a t i o n a l Assignment Dibenzothiophene-d  o f D i b e n z o t h i o p t i e n e - h and  from I n f r a r e d and Raman S p e c t r a . . . 153  o A.  Introduction  B.  S e l e c t i o n Rules  C.  The I n f r a r e d Spectrum  156  D.  Raman S p e c t r a  163  E.  Raman A c t i v e L a t t i c e Modes  168  F.  Assignment o f Fundamentals  G.  I n f r a r e d and Raman S p e c t r a o f D i b e n z o t h i o p h e n e - d g  •H. I. J.  The Assignment  153 -  o f t h e Fundamentals  153  . .•  . ....  172  o f D i b e n z o t h i o p h e n e - d 183 0  o  Normal C o o r d i n a t e C a l c u l a t i o n Discussion  Chapter 9  170  A Study o f Some E l e c t r o n i c S t a t e s o f D i b e n z o t h i o p h e n e .  186 187 191  A.  Introduction  191  B.  A b s o r p t i o n Spectrum  191  C.  Fluorescence Spectra  194  D.  Phosphorescence  1^8  E.  Discussion  C h a p t e r 10  Spectra  A Study o f B i p h e n y l C r y s t a l Phosphorescence by I m p u r i t i e s  203  Induced 206  -  Vlll  -  A.  Introduction  206  B.  Carbazole i n Biphenyl  207  C.  Dibenzothiophene  213  (  Appendix I  i n Biphenyl  A b s o r p t i o n and F l u o r e s c e n c e S p e c t r a o f C a r b a z o l e i n a Biphenyl Matrix  Appendix I I  A Comparison o f the Fundamental V i b r a t i o n s o f Carbaz o l e , F l u o r e n e and D i b e n z o t h i o p h e n e  References  219  227  230  - ix L i s t o f Figures  1.  P o s s i b l e s t r u c t u r e s f o r t h e i m p u r i t y g i v i n g t h e weak absorpo  t i n g a t 3200 A.  I benz[f]indan; I I benz[e]indan;  dihydrophenalene  '  I I I 2,330  2. 3.  NMR spectrum o f b e n z [ f ] i n d a n H e l i u m gas thermometer  31 35  4.  E x t e r n a l o p t i c a l system used f o r a b s o r p t i o n and luminescence e x p e r i m e n t s  3 7  5.  Biphenyl u n i t c e l l  4  6.  Fluorene u n i t c e l l  7.  Bond l e n g t h s and bond a n g l e s o f c a r b a z o l e  4  5  8.  Carbazole u n i t c e l l  4  3  ..  3  43  • 9.  Dibenzothiophene u n i t c e l l  46  10.  Bond l e n g t h s and bond a n g l e s o f d i b e n z o t h i o p h e n e  4  11.  Low f r e q u e n c y  51  12.  Infrared spectra of carbazole  13.  Some low f r e q u e n c y  14.  Raman s p e c t r a o f c a r b a z o l e  15.  The f l u o r e s c e n c e spectrum o f c a r b a z o l e i n a s i n g l e  i n f r a r e d spectra of carbazole  59  Raman i n t e r v a l s o f c a r b a z o l e  61 crystal 63  m a t r i x o f f l u o r e n e a t about 15°K 16.  In-plane i n t e r n a l coordinate d e f i n i t i o n s of carbazole  17.  C a l c u l a t e d normal c o o r d i n a t e s f o r two A^ fundamentals  73  81  of carbazole 18.  7  The p o l a r i z e d a b s o r p t i o n spectrum o f c a r b a z o l e i n f l u o r e n e at  about 15°K  "  •  84  -  19.  X  -  A microdensitometer t r a c i n g of the p o l a r i z e d absorption spectrum o f b e n z [ f ] i n d a n i n f l u o r e n e a t about 25°k  20.  96  A microdensitometer t r a c i n g o f the p o l a r i z e d fluorescence spectrum o f b e n z [ f ] i n d a n i n f l u o r e n e a t about 15°K  21.  102  F a c t o r group s p l i t t i n g s a s s o c i a t e d w i t h t h e l o n g - and s h o r t - a x i s o f f l u o r e n e c a l c u l a t e d f o r t r a n s i t i o n moments o f 0.237  A.  22.  The room t e m p e r a t u r e a b s o r p t i o n s p e c t r a o f f l u o r e n e  23.  The a b s o r p t i o n s p e c t r a o f f l u o r e n e a t l i q u i d h e l i u m  H2 H3  t e m p e r a t u r e s (a) i n a n-heptane m a t r i x and (b) f o r bp o l a r i z a t i o n i n an ab c r y s t a l s e c t i o n 24.  The f l u o r e s c e n c e s p e c t r a o f f l u o r e n e a t ^ 15°K f o r a be s e c t i o n o f t h e s i n g l e c r y s t a l and i n a n-heptane m a t r i x  25.  116  ...  The t r i p l e t - t r i p l e t a b s o r p t i o n spectrum o f f l u o r e n e i n nheptane a t > 15°K  26.  H8  127  The phosphorescence o f f l u o r e n e i n t h e c r y s t a l a t °o 6°K when i n d u c e d by t h e a d d i t i o n o f d i b e n z o t h i o p h e n e i m p u r i t y and i n n-heptane a t ^ 15°K  27.  The i n f r a r e d spectrum o f f l u o r e n e i n a c y c l o h e x a n e s o l u t i o n i n t h e low-frequency r e g i o n  28.  128  134  The p o l a r i z e d i n f r a r e d s p e c t r a o f f l u o r e n e s i n g l e c r y s t a l a t low f r e q u e n c i e s  135  29.  I n f r a r e d s p e c t r a o f f l u o r e n e i n t h e CH s t r e t c h i n g r e g i o n . . .  1^5  30.  The p o l a r i z e d i n f r a r e d s p e c t r a o f a f l u o r e n e s i n g l e c r y s t a l  135  31.  The Raman s p e c t r a o f a f l u o r e n e s i n g l e c r y s t a l  141  - xi -  32.  The Raman s p e c t r a and  33.  of a fluorene  s i n g l e c r y s t a l showing A  2  modes  142  The p o l a r i z e d  i n f r a r e d spectrum o f d i b e n z o t h i o p h e n e i n t h e  low f r e q u e n c y r e g i o n 34.  157  The p o l a r i z e d i n f r a r e d s p e c t r a  o f a dibenzothiophene  single crystal 35.  158  The i n f r a r e d spectrum o f d i b e n z o t h i o p h e n e i n c y c l o h e x a n e and benzene s o l u t i o n s  36.  i n t h e low f r e q u e n c y r e g i o n  159  The i n f r a r e d spectrum o f d i b e n z o t h i o p h e n e i n c a r b o n disulphide,  carbon t e t r a c h l o r i d e and  tetrachloroethylene  solutions  159  37.  The Raman s p e c t r a  o f a d i b e n z o t h i o p h e n e s i n g l e c r y s t a l ....  164  38.  The Raman s p e c t r a  o f a dibenzothiophene s i n g l e c r y s t a l  165  39.  The i n f r a r e d spectrum o f d i b e n z o t h i o p h e n e - d  single crystal o  i n t h e low f r e q u e n c y r e g i o n  173  40.  The i n f r a r e d spectrum o f d i b e n z o t h i o p h e n e s i n g l e c r y s t a l . . .  174  41.  I n f r a r e d spectrum o f d i b e n z o t h i o p h e n e - d disulphide,  c a r b o n t e t r a c h l o r i d e and  i n carbon  tetrachloroethylene  solutions 42.  175  I n f r a r e d spectrum o f d i b e n z o t h i o p h e n e - d g i n c y c l o h e x a n e s o l u t i o n i n t h e low f r e q u e n c y r e g i o n  :  176  43.  Raman s p e c t r a  o f dibenzothiophene-d  181  44.  Raman s p e c t r a  o f dibenzothiophene-d  182  o 45.  In-plane i n t e r n a l coordinates o f dibenzothiophene  187  - xii -  46.  A b s o r p t i o n s p e c t r a o f d i b e n z o t h i o p h e n e i n n-heptane and f l u o r e n e a t about 15°K  47.  192  D i b e n z o t h i o p h e n e f l u o r e s c e n c e i n (a) a f l u o r e n e m a t r i x , (b) t h e c r y s t a l , and (c) an n-heptane s o l u t i o n a t about 15°K....  48.  195  Phosphorescence s p e c t r a o f d i b e n z o t h i o p h e n e i n (a) hexamethylbenzene, (b) t h e c r y s t a l , and (c) n-heptane s o l u t i o n a t about 15°K  49.  199  Phosphorescence s p e c t r a o f b i p h e n y l c r y s t a l s doped w i t h c a r b a z o l e and d i b e n z o t h i o p h e n e  50.  208  Temperature v a r i a t i o n o f t h e i n t e n s i t y o f t h e phosphorescence and o f t h e d e l a y e d  f l u o r e s c e n c e from a b i p h e n y l  c r y s t a l doped w i t h c a r b a z o l e 51.  211  P l o t s o f l o g ( i n t e n s i t y r a t i o s ) v s . 1/T f o r t h e c a r b a z o l e / 212 b i p h e n y l system  52.  Temperature v a r i a t i o n o f t h e i n t e n s i t y o f t h e phosphorescence and o f t h e d e l a y e d  f l u o r e s c e n c e from a b i p h e n y l  c r y s t a l doped w i t h d i b e n z o t h i o p h e n e - h g 53.  215  P l o t s o f l o g ( i n t e n s i t y r a t i o s ) v s . 1/T f o r t h e d i b e n z o t h i o p h e n e - h / b i p h e n y l system  216  o 54.  T r i p l e t - t r i p l e t a b s o r p t i o n i n t h e b i p h e n y l c r y s t a l doped w i t h dibenzothiophene-h  a t about 10°K and t h e t r i p l e t -  o triplet  a b s o r p t i o n spectrum o f b i p h e n y l i n a r i g i d  glass  at 77°K 55.  217  Temperature v a r i a t i o n o f t h e i n t e n s i t y o f t h e phosphorescence and o f t h e d e l a y e d  f l u o r e s c e n c e from a b i p h e n y l  c r y s t a l doped w i t h d i b e n z o t h i o p h e n e - d  218  - Xlll  56.  The p o l a r i z e d a b s o r p t i o n spectrum o f c a r b a z o l e i n b i p h e n y l at about 15°K  57.  -  .  222  The f l u o r e s c e n c e spectrum o f c a r b a z o l e i n b i p h e n y l a t about 15°K  226  - xiv L i s t of Tables  1.  D i r e c t i o n cosines of biphenyl  42  2.  D i r e c t i o n cosines of fluorene  .44  3.  D i r e c t i o n cosines of carbazole  44  4.  D i r e c t i o n cosines of dibenzothiophene  47  5.  D i r e c t i o n cosines of dibenzothiophene  47  6.  C o r r e l a t i o n t a b l e showing t h e s e l e c t i o n r u l e s f o r t h e i s o l a t e d m o l e c u l e and f o r t h e c r y s t a l  7.  The i n f r a r e d spectrum o f c a r b a z o l e  8.  R e l a t i v e i n f r a r e d band i n t e n s i t i e s o f c a r b a z o l e  9. 10.  53 along  t h e c r y s t a l axes c a l c u l a t e d f o r t h e o r i e n t e d gas model ...  56  The Raman spectrum o f c a r b a z o l e  59  The f l u o r e s c e n c e spectrum o f c a r b a z o l e i n f l u o r e n e a t about 15°K  64  11.  The i n - p l a n e f o r c e c o n s t a n t s o f c a r b a z o l e  75  12.  V a l u e s o f t h e o u t - o f - p l a n e f o r c e c o n s t a n t s o f benzene ....  77  13.  A.comparison o f t h e observed and c a l c u l a t e d fundamentals of carbazole  14.  78  The a b s o r p t i o n spectrum o f c a r b a z o l e i n f l u o r e n e at about 15°K  15.  85  C o r r e l a t i o n between fundamentals o f the ground and  first  excited s t a t e of carbazole 16.  D i s t r i b u t i o n o f the m o l e c u l a r fundamentals o f b e n z [ f ] indan  17.  90  '  95  The p o l a r i z e d a b s o r p t i o n spectrum o f b e n z [ f ] i n d a n i n fluorene  97  -  18.  XV  -  The p o l a r i z e d f l u o r e s c e n c e spectrum o f b e n z [ f ] i n d a n i n fluorene  19.  100  C o r r e l a t i o n between fundamentals o f t h e ground s t a t e and f i r s t excited e l e c t r o n i c states of benz[f]indan  20.  104  The e x c i t e d - s t a t e c r y s t a l w a v e f u n c t i o n s and t h e i r i r r e d u c i b l e r e p r e s e n t a t i o n s i n t h e space group c o r r e l a t e d w i t h the f r e e molecule t r a n s i t i o n s  21.  D i p o l e - d i p o l e i n t e r a c t i o n sums f o r c r y s t a l l i n e  108 fluorene  o  o v e r a sphere o f 40 A r a d i u s f o r u n i t t r a n s i t i o n moments.. 22.  Calculated c r y s t a l levels of fluorene  23.  The a b s o r p t i o n spectrum t a k e n a t about 15°K o f f l u o r e n e crystal  24.  (ab f a c e ) and o f f l u o r e n e i n an :n-heptane m a t r i x . .  The t r i p l e t - t r i p l e t  a b s o r p t i o n spectrum o f f l u o r e n e i n 126  The phosphorescence spectrum o f f l u o r e n e i n a c r y s t a l .doped w i t h d i b e n z o t h i o p h e n e . a t about 6°K  27.  120  123  n-heptane a t about 15°K 26.  113  The f l u o r e s c e n c e spectrum o f f l u o r e n e i n n-heptane a t 15°K  25.  I l l  130  C o r r e l a t i o n t a b l e showing s e l e c t i o n r u l e s f o r t h e i s o l a t e d m o l e c u l e and f o r t h e c r y s t a l o f f l u o r e n e  133  - xvi -  28.  The r e l a t i v e band i n t e n s i t i e s o f f l u o r e n e a l o n g t h e c r y s t a l axes c a l c u l a t e d  i n the oriented-gas approximation . . —  ...  29.  The i n f r a r e d  spectrum o f f l u o r e n e  30.  The Raman spectrum o f f l u o r e n e near t h e e x c i t i n g  31.  The Raman spectrum o f f l u o r e n e  32.  The assignments o f t h e fundamental v i b r a t i o n s  of fluorene.  33.  C o r r e l a t i o n t a b l e showing t h e s e l e c t i o n  f o r the i s o -  137 line..... .  rules  l a t e d m o l e c u l e and t h e c r y s t a l o f d i b e n z o t h i o p h e n e 34.  Relative infrared  35.  The i n f r a r e d  .......  band i n t e n s i t i e s a l o n g t h e c r y s t a l  of dibenzothiophene c a l c u l a t e d  f o r t h e o r i e n t e d - g a s model..  144 149  154  1^5  spectrum o f d i b e n z o t h i o p h e n e i n t h e c r y s t a l .1^0  Raman s p e c t r a o f d i b e n z o t h i o p h e n e i n carbon solution  143  axes  and s o l u t i o n 36.  137  and a s i n g l e  tetrachloride  crystal  ;.  37-  Raman spectrum o f d i b e n z o t h i o p h e n e near t h e e x c i t i n g  38.  R e l a t i v e i n t e n s i t i e s o f Raman a c t i v e  light  168  modes due t o r o t a t i o n -  a l o s c i l l a t i o n s about t h e x_, y_, z_-molecular axes among t h e various polarized  spectra  39.  The i n f r a r e d  40.  The Raman spectrum o f d i b e n z o t h i o p h e n e - d exciting  spectrum o f d i b e n z o t h i o p h e n e - d g Q  177  c r y s t a l near t h e  line  181  41.  The Raman spectrum o f d i b e n z o t h i o p h e n e - d g c r y s t a l  42.  Moments o f i n e r t i a about t h e m o l e c u l a r axes o f d i b e n z o thiophene  43.  In-plane force constants o f dibenzothiophene  ........  182  186 ,  187  - xvii -  44.  A comparison o f t h e observed and c a l c u l a t e d fundamentals f o r dibenzothiophene-h  and - d  o 45.  o  A b s o r p t i o n s p e c t r a o f d i b e n z o t h i o p h e n e i n hexamethylbenzene (11MB) and n-heptane  46.  196  Phosphorescence s p e c t r a o f d i b e n z o t h i o p h e n e i n n-heptane  at about 15°K  .  (HMB)  m a t r i x , and  crystal  s  ...  219  The f l u o r e s c e n c e spectrum o f c a r b a z o l e i n b i p h e n y l a t about 15°K  50.  200  The a b s o r p t i o n spectrum o f c a r b a z o l e i n b i p h e n y l at about 15°K  49.  193  s o l u t i o n a t about 15°K  s o l u t i o n , hexamethylbenzene  48.  at about 15°K  D i b e n z o t h i o p h e n e f l u o r e s c e n c e i n a f l u o r e n e m a t r i x , the c r y s t a l and n-heptane  47.  189  Q  223  A comparison o f the assignments o f the fundamentals f o r c a r b a z o l e , f l u o r e n e , d i b e n z o t h i o p h e n e - h , and d i b e n z o t h i o 8 phene-dg . . .  227  - XV111 -  Acknowledgements  To Dr. A. B r e e , t h e s i s s u p e r v i s o r , t o whom I e x p r e s s my a p p r e c i a t i o n f o r h i s g u i d a n c e and c o n t i n u o u s s u p p o r t throughout t h e d u r a t i o n o f t h i s work, t o M i s s V.V. V i l k o s , f o r v a l u a b l e a s s i s t a n c e w i t h e x p e r i m e n t a l p r o c e d u r e s and f o r many h e l p f u l  discussions,  t o Dr. K.B. Harvey, who r e a d i l y made t h e i n f r a r e d equipment a v a i l a b l e , and t o Mr. R. Green, f o r i n s t r u c t i o n  i n t h e use o f  t h i s equipment, t o Dr. R. S c h a f f r i n and Dr. J . T r o t t e r , who g e n e r o u s l y made t h e c r y s t a l s t r u c t u r e data o f dibenzothiophene  available,  t o S. Whitlow, who l o c a t e d t h e c r y s t a l axes i n t h e melt-grown samples o f c a r b a z o l e and d i b e n z o t h i o p h e n e ,  t o Dr. M. K u r a h a s h i , who s u p p l i e d d e t a i l s o f t h e c a r b a z o l e c r y s t a l structure prior to publication,  t o Dr. S.C. W a i t , J r . , f o r p r o v i d i n g d e t a i l s o f h i s . w o r k b e f o r e i t was p u b l i s h e d ,  t o many o t h e r i n d i v i d u a l s , f o r t h e i r a s s i s t a n c e and c o n t r i b u t i o n s i n t h e p r e p a r a t i o n o f t h i s work, thank you.  Chapter 1 General I n t r o d u c t i o n  A.  I n t r o d u c t o r y Remarks In t h e p a s t 20 y e a r s the s p e c t r a o f o r g a n i c m o l e c u l a r c r y s t a l s have  been e x t e n s i v e l y s t u d i e d t o g a i n a more complete u n d e r s t a n d i n g o f i n t e r m o l e c u l a r as w e l l as i n t r a m o l e c u l a r p r o p e r t i e s . P r o g r e s s was facilitated  greatly  by the i n t r o d u c t i o n o f h i g h speed computers which c o u l d be  used t o t e s t t h e o r i e s i n v o l v i n g complex c a l c u l a t i o n s o f m o l e c u l a r  orbitals,  of m u l t i p o l e i n t e r a c t i o n s i n c r y s t a l s , a n d of v i b r a t i o n a l frequencies.  The  development o f i n t e n s e UV l i g h t s o u r c e s f o r a b s o r p t i o n ' a n d e m i s s i o n s t u d i e s , l a s e r Raman s p e c t r o m e t e r s , and i n f r a r e d p o l a r i z e r s and  spectrometers  e x t e n d i n g i n t o t h e f a r i n f r a r e d has made a v a i l a b l e more complete s e t s o f e x p e r i m e n t a l d a t a which i n t u r n has r e s u l t e d i n more a c c u r a t e i n t e r p r e t a t i o n s o f many phenomena a s s o c i a t e d w i t h o r g a n i c m o l e c u l e s  and  crystals.  The p r e s e n t i n v e s t i g a t i o n i s concerned w i t h t h e e l e c t r o n i c and  vibration-  a l p r o p e r t i e s o f some t r i c y c l i c a r o m a t i c and h e t e r o a r o m a t i c compounds. aim o f t h i s r e s e a r c h i s t o use the a l r e a d y w e l l - e s t a b l i s h e d  The  experimental  t e c h n i q u e s o f i n f r a r e d , Raman and low-temperature UV s p e c t r o s c o p y t o g a t h e r t h e d a t a and t o i n t e r p r e t t h e d a t a w i t h i n t h e framework o f t h e existing  theories.  Thus t h i s f i r s t  c h a p t e r o u t l i n e s r e l e v e n t p a r t s o f the t h e o r i e s o f  v i b r a t i o n a l - e l e c t r o n i c i n t e r a c t i o n s , excitons i n molecular c r y s t a l s , normal c o o r d i n a t e a n a l y s i s .  and  More s p e c i f i c d e t a i l s o f t h e t h e o r y are g i v e n  -  2 -  as t h e y a r e needed and used t o e l u c i d a t e some a s p e c t o f t h e phenomenon under investigation.  Chapter  2 describes the general experimental  techniques  t h a t were used t o p u r i f y t h e m a t e r i a l s , grow and c u t t h e s i n g l e samples,  and o b t a i n t h e s p e c t r a .  The c o n t e n t o f c h a p t e r s 3-10 i s comprised  o f t h e Raman, i n f r a r e d , luminescence degrees o f completeness  crystal  and a b s o r p t i o n s p e c t r a i n v a r y i n g  w i t h r e s p e c t t o t h e number o f t y p e s o f s p e c t r a and  t h e e x t e n s i v e n e s s o f t h e i n v e s t i g a t i o n o f a p a r t i c u l a r t y p e o f spectrum for  each o f t h e m o l e c u l e s c a r b a z o l e , b e n z [ f ] i n d a n , f l u o r e n e , and d i b e n z o -  thiophene.  The a c t u a l d i v i s i o n o f e x p e r i m e n t a l r e s u l t s among t h e c h a p t e r s  and t h e sequence o f t h e c h a p t e r s was d e c i d e d upon a c c o r d i n g t o t h e compound b e i n g i n v e s t i g a t e d and t h e r e l a t i v e c e r t a i n t y o f i t s v i b r a t i o n a l Thus c h a p t e r 3 c o n t a i n s a f a i r l y complete  assignment.  d i s c u s s i o n o f the v i b r a t i o n s o f  c a r b a z o l e from t h e i n f r a r e d , Raman and f l u o r e s c e n c e s p e c t r a as w e l l as t h e calculated frequencies.  The v i b r a t i o n s and p o l a r i z a t i o n p r o p e r t i e s o f t h e  f i r s t e x c i t e d s i n g l e t s t a t e o f c a r b a z o l e a r e d e a l t w i t h i n c h a p t e r 4.  In  c h a p t e r 5, t h e d i s c u s s i o n o f t h e i m p u r i t i e s o f f l u o r e n e p r e p a r e s t h e way f o r t h e s t u d y o f some e x c i t e d s i n g l e t and t r i p l e t e l e c t r o n i c s t a t e s o f f l u o r e n e which f o l l o w s i n c h a p t e r 6.  The v i b r a t i o n a l assignment o f f l u o r e n e  in c h a p t e r 7 from t h e i n f r a r e d and Raman s p e c t r a i s c o r r e l a t e d w i t h t h e assignments  f o r carbazole.  The i n v e s t i g a t i o n o f t h e v i b r a t i o n s o f d i b e n z o -  t h i o p h e n e and d i b e n z o t h i o p h e n e - d g of  i s reported f o r the f i r s t time.  some e x c i t e d t r i p l e t and s i n g l e t s t a t e s o f d i b e n z o t h i o p h e n e  in c h a p t e r 9.  F i n a l l y , c h a p t e r 10 d e a l s w i t h some u n u s u a l  A study  i s contained  energy-trapping  e f f e c t s t h a t a r o s e from a s t u d y o f t h e phosphorescence s p e c t r a o f t h e s i n g l e c r y s t a l systems made up o f c a r b a z o l e and d i b e n z o t h i o p h e n e added as i m p u r i t i e s t o b i p h e n y l o r f l u o r e n e m a t r i c e s .  deliberately  B.  The Theory o f V i b r a t i o n a l - E l e c t r o n i c I n t e r a c t i o n s The  i n t e n s i t y o f an o p t i c a l ( e l e c t r i c d i p o l e ) t r a n s i t i o n i s p r o p o r t i o n a l  to. t h e square o f t h e t r a n s i t i o n moment between t h e i n i t i a l and f i n a l  states.  The t r a n s i t i o n moment between two s t a t e s i and j i s  =y*Y CxiX)M(x,X)¥ (x,X)dxdX  Mj ±  i  j  ,  .  where 1^(x,X) and ^ (x,X) a r e e x a c t s o l u t i o n s o f t h e S c h r o d i n g e r f o r t h e complete H a m i l t o n i a n .  (1.1)  equation  The c o l l e c t i v e c o o r d i n a t e symbols x and X form  a complete s e t o f i n t e r n a l c o o r d i n a t e s and l o c a t e r e s p e c t i v e l y a l l o f t h e e l e c t r o n s and n u c l e i .  M(x,X) i s t h e d i p o l e moment o p e r a t o r  M(x,X) = e£r. - eEZ R l where r . and R  (1.2)  a r e t h e p o s i t i o n v e c t o r s o f t h e i t h e l e c t r o n and c t h n u c l e u s  respectively. I n p o l y a t o m i c systems e x a c t s o l u t i o n s a r e n o t known s i n c e t h e e q u a t i o n s o f m o t i o n o f t h r e e o r more i n t e r a c t i n g p a r t i c l e s cannot be s o l v e d .  The  Born-Oppenheimer approximation"''is used t o o b t a i n a s i m p l i f i c a t i o n o f t h e mathematical  d e s c r i p t i o n o f t h e system.  e l e c t r o n i c and n u c l e a r m o t i o n s .  This procedure  separates the  The a d i a b a t i c w a v e f u n c t i o n s  are usually  f u r t h e r s i m p l i f i e d by f i x i n g t h e n u c l e a r c o o r d i n a t e s which appear as p a r a meters i n t h e e l e c t r o n i c w a v e f u n c t i o n s .  Thus t h e z e r o t h - o r d e r v i b r o n i c wave-  f u n c t i o n f o r t h e p t h v i b r a t i o n a l l e v e l o f t h e i t h e l e c t r o n i c s t a t e can be w r i t t e n as t h e p r o d u c t  function  ¥."(x,X) = i>. (x,X' ) x ly l o ly  (X)  (1.3)  -  4  -  where <J^ ( x , X ) i s a s o l u t i o n o f t h e e l e c t r o n i c S c h r o d i n g e r e q u a t i o n f o r t h e equilibrium nuclear  configuration X  and  q  X _  Y  i s t h e v i b r a t i o n a l wave-  ( X )  function. S i n c e most i n f o r m a t i o n  c o n c e r n i n g t h e n u c l e a r motions o f p o l y a t o m i c  m o l e c u l e s r e l a t e s t o t h e ground s t a t e , i t i s c o n v e n i e n t t o e x p r e s s t h e nuclear  coordinates  for that state.  X i n terms o f a complete s e t o f normal c o o r d i n a t e s  The normal c o o r d i n a t e s  i n f i n i t e s i m a l nuclear  displacements.  Q  c o m p l e t e l y span t h e space o f  With a p p r o p r i a t e  choice o f o r i g i n ,  the e l e c t r o n i c w a v e f u n c t i o n s b e l o n g i n g t o t h e e x c i t e d e l e c t r o n i c s t a t e s may be e x p r e s s e d i n terms o f t h e ground s t a t e Q.  Thus t h e v i b r o n i c w a v e f u n c t i o n  f o r u quanta o f any one normal mode i n t h e k t h e x c i t e d e l e c t r o n i c s t a t e i s  \ .  \y  ( x  '  Q )  =  *k  ( x  ' o Q  where t h e g e n e r a l d i s p l a c e m e n t v e c t o r  ) x  ky  ( Q  '  A )  ( 1  -  4 )  A accounts f o r t h e d i f f e r e n c e i n t h e  e q u i l i b r i u m geometry between t h e ground and e x c i t e d e l e c t r o n i c s t a t e s . The  AE g r e a t e r  number o f m o l e c u l e s i n a s t a t e w i t h energy  l o w e s t energy s t a t e i s g i v e n by t h e B o l t z m a n n d i s t r i b u t i o n  than t h e  f a c t o r exp(-AE/kT)  so t h a t , a t v e r y low t e m p e r a t u r e s , o n l y t h e z e r o t h v i b r a t i o n a l l e v e l o f t h e ground s t a t e w i l l be p o p u l a t e d .  The p r o b a b i l i t y o f t h e t r a n s i t i o n from t h e  z e r o t h v i b r a t i o n a l l e v e l o f t h e ground s t a t e t o t h e u t h v i b r a t i o n a l l e v e l o f t h e k t h e x c i t e d s t a t e i s p r o p o r t i o n a l t o t h e square o f t h e t r a n s i t i o n moment  Vkp  \^0^^o  ) X  00WHe^ -ep R }* (x,Q )x i  a  a  o  k  k y  (Q A)dxdQ 3  1 =  M (Q )/x (Q)x (Q A)dQ0k  o  00  ky  3  -  -  (1.5) -  where  '/x oCQ)x (Q.A)dQ  and  0  i s t h e Frank-Condon o v e r l a p f a c t o r .  (1.5)  kM  H i e c o n t r i b u t i o n from t h e o p e r a t o r  eEZ R v a n i s h e s i n t h e i n t e g r a t i o n over t h e e l e c t r o n i c c o o r d i n a t e s , a a~a Equation tion.  (1.5) a c c o u n t s  f o r a number o f f e a t u r e s o f a v i b r o n i c  transi-  The v e c t o r M , (Q ) has a d e f i n i t e o r i e n t a t i o n i n r e l a t i o n t o t h e -Ok ^ x r n  m o l e c u l a r s k e l e t o n and t h e r e f o r e p r e d i c t s t h e p o l a r i z a t i o n o f t h e t r a n s i t i o n . 2 Group t h e o r e t i c a l or f o r b i d d e n .  c o n s i d e r a t i o n s c l a s s i f y t h e t r a n s i t i o n as symmetry a l l o w e d  The e l e c t r o n i c t r a n s i t i o n i s s a i d t o be e l e c t r i c d i p o l e  allowed i f the decomposition o f the d i r e c t product o f the i r r e d u c i b l e r e p r e s e n t a t i o n s o f ip (x,Q ) , r . , and u), (x,Q ) c o n t a i n s t h e t o t a l l y symmetric n  0  0  1  r e p r e s e n t a t i o n o f t h e p o i n t group.  K  O  O t h e r w i s e , ,M^(Q) v a n i s h e s and t h e  t r a n s i t i o n i s symmetry f o r b i d d e n . An abundance o f e x p e r i m e n t a l e v i d e n c e shows t h a t t h e t r a n s i t i o n moment o s p e c t r a . The c l a s s i c example i s t h e weak benzene a b s o r p t i o n system a t 2600 A as d e f i n e d i n e q u a t i o n (1.5) does n o t g i v e an adequate account o f v i b r o n i c which i s symmetry f o r b i d d e n and shows a p r o g r e s s i o n i n t o t a l l y symmetric v i b r a t i o n s b u i l t upon s i n g l e quanta o f n o n - t o t a l l y symmetric v i b r a t i o n s  which  3 a c t as, " f a l s e o r i g i n s " .  A t h e o r e t i c a l treatment t o account  f o r t h e appear-  ance o f t h e s e " f o r b i d d e n " components i n t h e t r a n s i t i o n s o f p o l y a t o m i c m o l 4 e c u l e s by v i b r o n i c m i x i n g was f o r m u l a t e d by Herzberg and T e l l e r . The t h e o r y 5 6 7 has been r e f i n e d and extended by L i e h r , M u r r e l l and P o p l e , Craig, 8 9 A l b r e c h t , and Yeranos. The b a s i s o f t h e H e r z b e r g - T e l l e r t h e o r y i s t o e x p r e s s t h e dependence o f t h e e l e c t r o n i c S c h r o d i n g e r e q u a t i o n on t h e m o t i o n o f t h e n u c l e i as a  - 6 -  perturbation.  The e l e c t r o n i c H a m i l t o n i a n i s expanded as a power s e r i e s i n  t h e normal c o o r d i n a t e s  about t h e e q u i l i b r i u m . p o s i t i o n o f t h e ground s t a t e  as q  where H  q  H  i s t h e H a m i l t o n i a n f o r t h e e q u i l i b r i u m n u c l e a r c o n f i g u r a t i o n and  the p e r t u r b a t i o n i s  9H ECTTJ )  Q  -  q ^  q  q  q  0  •  The p e r t u r b e d e l e c t r o n i c  wavefunction  q  ( '»Q) i s t h e n e x p r e s s e d  i n the b a s i s o f the unperturbed  (X,Q)E^°^  combination.  X  as t h e l i n e a r  V ' X  where  (E° - E°) X  Q )  fcl  =  +  wavefunctions  v-v  i j ki *?c  = f ^ ( ^  x  k  Q  % ^ %  d-8)  The ground s t a t e i s assumed n o t t o mix w i t h e x c i t e d s t a t e s s i n c e t h e v a l u e o f E^ - E° i s v e r y l a r g e ( u s u a l l y g r e a t e r than 20000 cm The t r a n s i t i o n moment c o r r e c t e d t o f i r s t o r d e r i n s m a l l is  displacements  then  •JWy where  =  M  0kWo^00^  M  Q l  (QT  k y  ( Q , A ) d Q + ^ M CQ )/xooCQ)^iX (Q,A).dQ k  01  0  =yjjM.(x^°dx 0  l0  (1.9)  The f i r s t term i n t h e e q u a t i o n r e p r e s e n t i n g t h e " a l l o w e d " p a r t o f t h e t r a n s i t i o n moment i n t e g r a l has a l r e a d y been d i s c u s s e d . i s p o l a r i z e d a c c o r d i n g t o t h e sense o f M ^ ( Q ) .  The " f o r b i d d e n " term  The c o n d i t i o n f o r t h e n o n - v a n i s h i n g  o f t h e n u c l e a r dependent o r  f o r b i d d e n term i n t h e t r a n s i t i o n moment e x p r e s s i o n • i s t h a t M^^ and X^ For f i n i t e MQ^J the d i r e c t  must be non-zero f o r a t l e a s t one s t a t e 1.  p r o d u c t o f t h e i r r e d u c i b l e r e p r e s e n t a t i o n s T (y>°), r ( E i \ ) , r(i|j°) must  contain  the t o t a l l y symmetric r e p r e s e n t a t i o n o f t h e p o i n t group o f t h e m o l e c u l e . For f i n i t e X^  of r ( ^ ) ,  the d i r e c t products  r(Qq),  T(X_Q)  tion.  These r e q u i r e m e n t s i m p l y  must s i m u l t a n e o u s l y  = r  o  o  =  ),  o  (1.10)  r(Er.)  i s i n v a r i a n t to the operations  of the point  has t h e same symmetry p r o p e r t i e s i n - e l e c t r o n  has i n n u c l e a r space.  a r e s p e c i f i e d , and T ( 3 H / 3 Q ^ )  k y  that  group o f t h e m o l e c u l e , (3H/9Q^) space t h a t  o  c o n t a i n t h e t o t a l l y symmetric r e p r e s e n t a -  r(^)xr(3H/3Q )  Further, since the Hamiltonian  r ( 3 H / 3 Q ^ ) , r(u>°), and r ( x  (1.10), r C ^ ) >d  In equation  ar  can be d e t e r m i n e d .  T(IJJ°)  This i s equivalent t o  s p e c i f y i n g t h e t y p e o f v i b r a t i o n t h a t can mix t h e e l e c t r o n i c s t a t e  with  <• A q u a n t i t a t i v e t r e a t m e n t o f t h e v i b r a t i o n a l borrowing v i a t h e 606 and. -1  1 e g v i b r a t i o n s between t h e a l l o w e d (1800A) e l e c t r o n i c s t a t e 1 ° i and t h e f o r b i d d e n (2650A) and (2000A) e l e c t r o n i c s t a t e s o f 1595 cm  2  benzene has been made.^  The c a l c u l a t i o n i n v o l v e s an e v a l u a t i o n o f A,,. kl The term i n H which depends on b o t h t h e e l e c t r o n s i and t h e n u c l e i a i s  1  i  Z e  E  2  o ±c£—  (1.11)  -io and t h e r e f o r e  — - = X {ZZ e % i = l cr a n  2  ____ . £ia }-=•?' h. Q q r. 1  9  3  i  =  1  „  '(1.12)  - 8 -  where r  i s t h e p o s i t i o n v e c t o r o f n u c l e u s a.  The n u c l e a r d i s p l a c e m e n t s i n 8r t h e normal modes a r e thus r e p r e s e n t e d by t h e s e t o f d i p o l e s eZ^ -r^rq i n t e r a c t i n g w i t h t h e e l e c t r o n s i . S i n c e e q u a t i o n (1.12) i s t h e sum o f one o  e l e c t r o n o p e r a t o r s h^ t h e c a l c u l a t i o n o f t h e i n t e g r a l i n 1.8 r e d u c e s t o t h e N i n t e g r a t i o n o f 1 h. w i t h t h e t r a n s i t i o n d e n s i t y , p, ..  1=1  P k l =JJ° ¥jdx' I k l  (1.13)  The  r e s u l t s o f t h e c a l c u l a t i o n ^ show t h a t the^E, s t a t e i s mixed most lu 1 -1 e f f e c t i v e l y with the s t a t e by t h e 6 0 6 cm v i b r a t i o n and w i t h t h e ^B^ s t a t e by t h e 1595 cm * v i b r a t i o n , lu 1  C.  The Franck-Condon P r i n c i p l e The  Franck-Condon p r i n c i p l e d e t e r m i n e s t h e i n t e n s i t y d i s t r i b u t i o n o f an  e l e c t r o n i c t r a n s i t i o n among i t s v i b r a t i o n a l members.  The p r i n c i p l e s t a t e s  t h a t t h e n u c l e a r p o s i t i o n s and v e l o c i t i e s do not change d u r i n g an e l e c t r o n i c transition. represents  That i s , t h e s t a r t i n g c o n f i g u r a t i o n i n t h e new e l e c t r o n i c s t a t e a d i s p l a c e m e n t from t h e new e q u i l i b r i u m n u c l e a r  w i t h o u t change o f symmetry.  configuration  I f the displacement o f t h e e q u i l i b r i u m  nuclear  c o n f i g u r a t i o n i s z e r o ( A = 0 ) and i f t h e p o t e n t i a l energy s u r f a c e s have t h e same shape i n b o t h e l e c t r o n i c s t a t e s , t h e n a l l t h e i n t e n s i t y i s c o n c e n t r a t e d in the  (0-0)  band.  I f t h e d i s p l a c e m e n t i s non-zero  h i g h e r v i b r o n i c s t a t e s become more p r o b a b l e .  (A,^0),  transitions to  The s t e e p n e s s o f t h e p o t e n t i a l  energy curve i n t h e e x c i t e d s t a t e d e t e r m i n e s t h e number o f e x c i t e d ' s t a t e v i b r a t i o n a l wavefunctions  X^CQJA)  which w i l l have a p p r e c i a b l e  the ground s t a t e v i b r a t i o n a l w a v e f u n c t i o n s  XQQ(Q)  a n  d therefore  overlap  with  the length of  - 9 -  t h e p r o g r e s s i o n i n an e l e c t r o n i c t r a n s i t i o n . The aromatic  dominant p r o g r e s s i o n t h a t appears i n the t r a n s i t i o n s o f p o l y a c e n e h y d r o c a r b o n s has a s p a c i n g o f about 1400  s p a c i n g i n t h e n a p h t h a l e n e spectrum i s 1378 Frequencies  o f about 1400  cm  e s s e n t i a l l y mixtures o f C-C  cm  * and  For example the i n a n t h r a c e n e 1401  cm  * a r e a t t r i b u t e d t o v i b r a t i o n s which a r e  ( s k e l e t a l ) and  i n - p l a n e C-H  comparison of the s p e c t r a of f u l l y deuterated w i t h the u n d e u t e r a t e d  cm  bending modes. A  n a p h t h a l e n e and  anthracene  s p e c i e s shows t h a t d e u t e r a t i o n has no marked e f f e c t  t h e s p e c t r a beyond a zero p o i n t energy s h i f t . ^  One  on  c o n c l u s i o n t o be  drawn from t h i s o b s e r v a t i o n i s t h a t shape changes i n the e x c i t e d s t a t e can be d e s c r i b e d p r e d o m i n a n t l y  i n terms o f C-C  bond l e n g t h s such t h a t no l o s s  o f c o v e r i n g symmetry o c c u r s . A number o f q u a n t i t a t i v e a p p l i c a t i o n s o f t h e Franck-Condon p r i n c i p l e have been made.  From a knowledge o f the i n t e n s i t y d i s t r i b u t i o n i n the benzene o  band system at 2650A and t h e v i b r a t i o n s a c t i v e i n f o r m i n g (ground s t a t e , 992  cm  e x c i t e d s t a t e , 923 cm  the  progression  ^ ) , t h e e x t e n s i o n of the  ' "'  ° 7  :  C-C  bond l e n g t h o f benzene i n t h e e x c i t e d s t a t e was  The  lowest benzene t r i p l e t s t a t e C-C  c a l c u l a t e d t o be 0.036 A.  bond l e n g t h e x t e n s i o n r e l a t i v e t o t h e °11  ground s t a t e was  c a l c u l a t e d t o be 0.036A  as w e l l .  The  b u t i o n among the v i b r a t i o n a l members o f a t r a n s i t i o n has  intensity  been c a l c u l a t e d  from the changes i n geometry, the f r e q u e n c i e s and the c o r r e s p o n d i n g A modes o fc +u t h e r e l! e v a n\ t v i-ub r a t i o n s i• n +u the p r o g r e s s i• o n . 10,12,13,14  D.  The  distri-  normal  Theory o f E x c i t o n s i n M o l e c u l a r C r y s t a l s  E s p e c i a l l y f o r t h e weaker t r a n s i t i o n s , the a b s o r p t i o n s p e c t r a i n the c r y s t a l r e s e m b l e the s o l u t i o n s p e c t r a i n band shape and  frequency,  For  example, t h e r e i s no d i f f i c u l t y i n c o r r e l a t i n g the p r i n c i p a l f e a t u r e s o f  - 10  the  c r y s t a l and  s o l u t i o n a b s o r p t i o n system o f medium i n t e n s i t y i n anthracene.'''  However, s i g n i f i c a n t d i f f e r e n c e s occur.  -  One' n o t a b l e d i f f e r e n c e  between the  c r y s t a l and  i s the f r e q u e n c y s h i f t o f the  along d i f f e r e n t d i r e c t i o n s  o f c r y s t a l symmetry.  are  S m a l l changes i n the  s p l i t i n the  crystal.  g e n e r a l d i s p l a c e m e n t t o the r e d The  not  i n t e r a c t and  t o as an  of the  In the  the o r d e r l y  "oriented  gas".  spectra  That i s , the  s i m i l a r i t y between the  arise.  molecules  c r y s t a l and  c r y s t a l can  t i o n of t h i s theory i s a v a i l a b l e b r i e f o u t l i n e o f the  essential  solution  the  but  the  A detailed and  c r y s t a l i s r e p r e s e n t e d by The  f r e e m o l e c u l e and  of l i g h t a l o n g the c r y s t a l l o g r a p h i c t r a n s i t i o n moment by  model.  energy l e v e l s c o r r e c t  e i g e n v a l u e s o f the  only a  the  i n t e n s i t y o f the  axes i s r e l a t e d  square o f the  t o the  a system o f  energy l e v e l s o f the  direction  t o the  system  are  absorption  f r e e molecule  cosines.  In r e a l c r y s t a l s the m o l e c u l e s are weakly i n t e r a c t i n g and the  considera-  i d e a s i s g i v e n below.  non-interacting molecules.  same as t h o s e o f the  inten-  be a c c o u n t e d f o r u s i n g  i n a number o f b o o k s ' ^ ^  In the u n p e r t u r b e d p r o b l e m , the oriented  gas  do  referred  s p e c t r a s u g g e s t s t h a t the p o l a r i z a t i o n , s p l i t t i n g , d i s p l a c e m e n t and  p e r t u r b a t i o n methods based on the o r i e n t e d  a  i n t h i s work r e p r e s e n t examples  zeroth order of approximation  s i t y d i s t r i b u t i o n of the bands i n the  polarized  i n t e n s i t y p a t t e r n and  a r r a y of n o n - i n t e r a c t i n g molecules i s  The  do  s o l u t i o n bands  s o l u t i o n band system a l s o  o r g a n i c s o l i d s under i n v e s t i g a t i o n  of m o l e c u l a r c r y s t a l s .  solution spectra  f i r s t order of approximation  therefore are  Hamiltonian  (1.14)  - 11 for a r i g i d l a t t i c e .  i s the H a m i l t o n i a n f o r t h e k t h m o l e c u l e , and  i s t h e p e r t u r b a t i o n o p e r a t o r between m o l e c u l e s k and  1.  The u n p e r t u r b e d o r ground s t a t e ($-.) o f t h e c r y s t a l i s g i v e n as t h e p r o d u c t f u n c t i o n o f the f r e e m o l e c u l e w a v e f u n c t i o n s  for a c r y s t a l of N molecules.  E l e c t r o n exchange i s n e g l e c t e d s i n c e o v e r l a p  between m o l e c u l a r w a v e f u n c t i o n s even o f n e i g h b o u r i n g m o l e c u l e s i s v e r y small.  Then t h e energy o f t h e ground s t a t e t o a f i r s t o r d e r o f  approxima-  tion i s  E  '  where w^  G  Sk  =  +  5k j l/^ kV l V k l 5  i s t h e m o l e c u l a r ground s t a t e  d T  (1  ' ^ 16  energy.  An u n p e r t u r b e d e x c i t e d s t a t e o f a c r y s t a l c o n s i s t s o f o n l y one  molecule  i n an e x c i t e d s t a t e , w h i l e a l l t h e o t h e r m o l e c u l e s a r e i n t h e i r ground so t h a t a l o c a l i z e d e x c i t a t i o n  <rT ip  =  state,  wavefunction i s  11 12  CT ip  .... h N/h  v  (1.17) 3  The m o l e c u l e i n i t s r t h e x c i t e d s t a t e i s l o c a t e d i n t h e i t h t r a n s l a t i o n a l set  of the pth u n i t c e l l .  c e l l s i n the c r y s t a l .  There a r e h m o l e c u l e s p e r u n i t c e l l and N/h  unit  When i n t e r m o l e c u l a r f o r c e s a r e c o n s i d e r e d , t h e N  degenerate w a v e f u n c t i o n s a r e not s t a t i o n a r y s t a t e s o f t h e c r y s t a l and must be combined t o g i v e t h e e i g e n s t a t e s o f t h e c r y s t a l  -  $  R  W )  =  Z  ip  c  r  X  12  (  -  ^  {1.181  cf,  r  P  X  P  rfil  The  eigenvalues  and c o e f f i c i e n t s c ^  JJ  a r e found by s o l v i n g  the secular  equation |<cj> | r  H  -p  |<{> >  _ < <f> | l|<}» >  r  r  jq  r  ip  E|  =  0  (1.19)  jq  The problem o f f i n d i n g t h e c o r r e c t l i n e a r c o m b i n a t i o n s may be s i m p l i f i e d c o n s i d e r a b l y by making use o f t h e symmetry o f t h e c r y s t a l and so t h e s e c u l a r equation  need n o t be s o l v e d i n t h i s form. 21  Space group t h e o r y has been d i s c u s s e d by Winston and H a l f o r d , ' '  22  Winston,  23  and K o s t e r . The r o l e o f t h e space group, s i t e group, f a c t o r group, t r a n s l a t i o n group and m o l e c u l a r p o i n t group i n t h e t h e o r y o f m o l e c u l a r 22  c r y s t a l s was s e t o u t i n a paper by Winston. The  Hamiltonian  has t h e f u l l symmetry o f t h e c r y s t a l and i s , t h e r e f o r e ,  i n v a r i a n t under t h e o p e r a t i o n s  o f t h e space group.  Linear combinations of  the l o c a l i z e d e x c i t a t i o n w a v e f u n c t i o n s can be c o n s t r u c t e d transform  so t h a t t h e y  l i k e i r r e d u c i b l e r e p r e s e n t a t i o n s o f t h e space group.  The  m o l e c u l e s form h t r a n s l a t i o n a l l y e q u i v a l e n t s e t s i n t h e c r y s t a l and assumi n g t h e c r y s t a l i s so l a r g e t h a t i t may be r e g a r d e d as h a v i n g number o f u n i t applied.  c e l l s i n a l l d i r e c t i o n s , p e r i o d i c boundary c o n d i t i o n s may be  Then f u n c t i o n s o f t h e form *?(k)  l  belonging  an i n f i n i t e  V  =  v/  h7N  /  £ e x p ( i k - r . ) 4> - -ip ip p T  r  (1.20)  t o t h e k t h r e p r e s e n t a t i o n o f t h e t r a n s l a t i o n group a r e c o n s t r u c t e d  r from t h e p r o d u c t f u n c t i o n s $^  i n which t h e m o l e c u l e s i n t h e i t h t r a n s l a t i o n a l l y  - 13 -  e q u i v a l e n t s e t are  i n their rth excited  t r a n s l a t i o n v e c t o r s and  vvavevectors  state.  The  vectors r.  -ip  and  k  -  are  respectively. x  F u r t h e r c l a s s i f i c a t i o n o f the o f k.  *^(k)  i s possible  only for special  In p a r t i c u l a r , the v a l u e k = 0 i s i m p o r t a n t i n o p t i c a l  In t h i s c a s e , a l l the u n i t c e l l f u n c t i o n s are i n phase and f o c u s s e d on o n l y one  unit c e l l .  The  values  transitions.  a t t e n t i o n may  be  functions = A/¥  *?(0)  E f  (1.21)  P are  c a l l e d one  throughout the Now  the  s i t e e x c i t o n s and c r y s t a l v i a one  f u n c t i o n s $_(0)  can  c o r r e s p o n d to the  spread o f the  excitation  t r a n s l a t i o n a l l y e q u i v a l e n t set o f m o l e c u l e s ,  be combined t o form e i g e n f u n c t i o n s o f the  crystal  which t r a n s f o r m l i k e i r r e d u c i b l e r e p r e s e n t a t i o n s o f the f a c t o r group. number o f c o m b i n a t i o n s c o r r e s p o n d s to the number o f m o l e c u l e s i n the cell.  The  from one  energy above the ground s t a t e o f the a t h  free molecule state  D" 1  T  .  ip,jq the prime on the  = Aw  k  r  p  and  a C r )  = Z''{<? C IV  I  unit  arising  is  AE  where  crystal state  The  °L  = <C  r  + D  T  +  r  t, > - < r  pq p q I V.  T  E'l  .  r  c  |V  (1.22)  I r  r >}  (1.23)  p q pq p q 1  .  k-  C  r  1  >  (1-24)  i p j q ip.jq i p j q 1  1  summation symbol i n d i c a t e s  that i p ^ j q .  The  quantity  x D  i s a coulomb i n t e r a c t i o n term and  r e p r e s e n t s the  o f a m o l e c u l e i n a c r y s t a l upon e x c i t a t i o n . bands o f the  The  change i n b i n d i n g energy  result is a shift in  c r y s t a l t o l o n g e r wavelengths r e l a t i v e t o t h o s e ; o f the  the  free  - 14 -  molecule.  i"  The q u a n t i t y I .  .  i s a resonance i n t e r a c t i o n i n t e g r a l and i s  a s s o c i a t e d w i t h t h e m i g r a t i o n o f energy from m o l e c u l e t o m o l e c u l e i n t h e crystal. Many o r g a n i c  crystals  have two m o l e c u l e s p e r u n i t c e l l .  The energy  d i f f e r e n c e between t h e two c r y s t a l s t a t e s a r i s i n g from t h e r t h m o l e c u l a r state i s  2 £ I. ip»2q r  q  T h i s i s known as t h e Davydov o r f a c t o r group s p l i t t i n g .  The s p l i t t i n g i s  the r e s u l t o f t h e i n t e r a c t i o n between t r a n s l a t i o n a l l y i n e q u i v a l e n t m o l e c u l e s in the c r y s t a l . E v a l u a t i o n o f t h e i n t e r a c t i o n i n t e g r a l i s c a r r i e d out by expanding the o p e r a t o r 1  V. as a s e r i e s o f p o i n t m u l t i p o l e - m u l t i p o l e ip,jq * .  terms.  24  The  l e a d i n g term i n t h e e x p a n s i o n i s t h e d i p o l e - d i p o l e i n t e r a c t i o n which can be c a l c u l a t e d from c r y s t a l l o g r a p h i c d a t a and from i n f o r m a t i o n from t h e s o l u t i o n spectrum o f t h e m o l e c u l e .  extracted  The d i p o l e - d i p o l e a p p r o x i m a t i o n 25  was s u c c e s s f u l l y a p p l i e d t o t h e a n t h r a c e n e c r y s t a l .  The shape dependence  o f t h e d i p o l e - d i p o l e sums was s t u d i e d and t h e summation o v e r a sphere was 26 found t o g i v e b e s t agreement w i t h  experiment.  D i f f e r e n t s t a t e s o f t h e m o l e c u l e o f t e n b e l o n g t o t h e same  representa-  t i o n o f t h e s i t e group and thus g i v e r i s e t o s t a t e s w i t h t h e same f a c t o r group r e p r e s e n t a t i o n . gap  Such s t a t e s a r e n o r m a l l y  so t h a t t h e i r i n t e r a c t i o n may be n e g l e c t e d  order  o f a p p r o x i m a t i o n by p e r t u r b a t i o n t h e o r y .  s e p a r a t e d by a wide energy o r t r e a t e d t o a second 27 C r a i g and Walmsley  have  shown t h a t a l t h o u g h t h e e f f e c t on t h e energy may not be l a r g e , t h e e f f e c t on t h e p o l a r i z a t i o n r a t i o i s i m p o r t a n t .  F o r example, i n a n t h r a c e n e t h e  - 15 -  calculated  polarization ratio I ^ l ;  a  to  a  f i r s t order o f approximation i s  7.8:1 and t o a second o r d e r o f a p p r o x i m a t i o n 2.3:1 f o r a s h o r t a x i s 25 transition. In t h e p r e c e d i n g d i s c u s s i o n ,  t h e Born-Oppenheimer s e p a r a b i l i t y o f t h e  electronic  and v i b r a t i o n a l w a v e f u n c t i o n s was assumed and o n l y t h e e l e c t r o n i c x w a v e f u n c t i o n s used i n d e f i n i n g t h e resonance i n t e g r a l I . . . However,  ip,jq  v i b r a t i o n a l e f f e c t s on t h e t r a n s f e r In weakly  o f energy  c o u p l e d systems, many v i b r a t i o n s  i n the c r y s t a l are important.  o c c u r b e f o r e t h e e x c i t a t i o n moves  to a n o t h e r m o l e c u l e , and so t h e m o l e c u l a r v i b r a t i o n s  f a c t o r group s p l i t t i n g i n each v i b r o n i c t h e spectrum electronic  i n t h e c r y s t a l have  band depends on i t s i n t e n s i t y i n  as determined by t h e Franck-Condon p r i n c i p l e .  I n t h e case t h a t  c o u p l i n g i s s t r o n g , t h e e x c i t a t i o n does n o t r e m a i n  localized  f o r a v i b r a t i o n a l p e r i o d and t h e d e t a i l o f t h e v i b r a t i o n a l s t r u c t u r e i s washed o u t .  E.  C o u p l i n g C r i t e r i a and D i s s i p a t i o n  of E x c i t a t i o n  Energy i n M o l e c u l a r  Crystals. C o u p l i n g c r i t e r i a were d e r i v e d by Simpson and P e t e r s o n . weak c o u p l i n g l i m i t , t h e i n t e r a c t i o n energy  where 2C i s t h e e l e c t r o n i c  «  1  In t h e  i s much l e s s t h a n t h e s e p a r a -  t i o n o f v i b r a t i o n a l l e v e l s and can be w r i t t e n  2C/A  28  i n t h e form  (1.25)  f a c t o r group s p l i t t i n g o b t a i n e d by c o n s i d e r i n g  t h e i n t e n s i t y as c o n c e n t r a t e d i n one m o l e c u l a r band, and A i s t h e w i d t h o f  - 16 -  the e n t i r e e l e c t r o n i c v i b r a t i o n a l spectrum.  The s t r o n g c o u p l i n g i n e q u a l i t y  is 2C/A  The  »  1  (1.26)  d i s s i p a t i o n o f r a d i a t i o n absorbed by a c r y s t a l c a n be  d i v i d e d i n t o two c a t e g o r i e s .  conveniently  F i r s t l y , t h e e x c i t a t i o n energy o f t h e c r y s t a l  may be t r a n s f o r m e d i n t o h e a t , and s e c o n d l y ,  i t may be r e - r a d i a t e d  (crystal  luminescence). Even f o r t h e second case when e x c i t e d v i b r o n i c s t a t e s o f t h e c r y s t a l a r e c r e a t e d , t h e t i m e s c a l e o f events i s f a v o u r a b l e  f o r the d i s s i p t i o n of  t h e v i b r a t i o n a l energy i n t o l a t t i c e modes so t h a t luminescence o r i g i n a t e s -12 from t h e p u r e e l e c t r o n i c s t a t e .  The phonon p e r i o d i s about 10 -8  i s v e r y s m a l l compared w i t h t h e normal l i f e t i m e  (a. 10  s e c , which  s e c ) o f an e x c i t e d  electronic state. In a c r y s t a l f r e e from d e f e c t s and u n d i s t u r b e d an e x c i t o n can p r o p a g a t e r a p i d l y . exciton w i l l  by l a t t i c e v i b r a t i o n s ,  The c o n d i t i o n s under which such a " f r e e " 29  l u m i n e s c e have been d i s c u s s e d  previously.  Generally, the  l u m i n e s c e n c e o f t h e e x c i t o n depends upon t h e s t r u c t u r e o f t h e B r i l l o u i n zone and r a t e s o f t h e decay p r o c e s s e s compared w i t h t h e l i f e t i m e o f t h e exciton. A n o t h e r p o s s i b l e decay r o u t e f o r t h e e x c i t o n o t h e r t h a n t h e t r a n s f o r m a t i o n i n t o heat and r a d i a n t energy i n v o l v e s t h e e x c i t o n t r a p p e d o r l o c a l i z e d at an i m p u r i t y m o l e c u l e o r l a t t i c e d e f e c t which has energy l e v e l s lower t h a n t h e e x c i t o n band.  The t r a p p e d e x c i t o n w i t h i t s energy l o c a l i z e d on  one m o l e c u l e behaves as a s i n g l e i s o l a t e d m o l e c u l e and such a m o l e c u l e may r a d i a t e t h e energy o r undergo o t h e r i n t e r n a l  processes.  - 17 -  F.  Mixed Molecular  C r y s t a l Systems  M i x e d c r y s t a l systems which c o n s i s t o f an i m p u r i t y  (guest)  introduced  i n s m a l l amounts i n t o a h o s t l a t t i c e have r e c e i v e d c o n s i d e r a b l e a t t e n t i o n . 30 The  c l a s s i c study o f n a p h t h a l e n e i n durene i s w e l l known.  The  ments o f a mixed c r y s t a l system are t h a t the h o s t be o p t i c a l l y i n t h e r e g i o n of i n t e r e s t and  require-  transparent  t h a t the guest m o l e c u l e s have a s i z e , shape,,  and o t h e r p h y s i c a l p r o p e r t i e s s i m i l a r t o t h e h o s t m o l e c u l e i n o r d e r s u b s t i t u t e at l a t t i c e The  to  sites.  e a r l i e s t mixed c r y s t a l s t u d i e s c o n s i d e r e d  guest-host i n t e r a c t i o n s  t o be v e r y weak and i n t e r p r e t e d the a b s o r p t i o n s p e c t r a on the b a s i s o f o r i e n t e d gas model.  The  experimental  observation  the  i s t h a t the e x c i t e d s t a t e s  o f p u r e c r y s t a l s are markedly m o d i f i e d by i n t e r m o l e c u l a r i n t e r a c t i o n s and i t i s expected t h a t the e n e r g i e s  o f mixed c r y s t a l s t a t e s w i l l a l s o show some  dependence on i n t e r m o l e c u l a r i n t e r a c t i o n s .  In p u r e c r y s t a l ' s resonance  exchange i n t e r a c t i o n takes p l a c e between i d e n t i c a l m o l e c u l a r t r e a t e d t o a f i r s t order o f p e r t u r b a t i o n t h e o r y .  l e v e l s and i s  On t h e o t h e r hand,  second o r d e r e f f e c t s i n p u r e c r y s t a l s depend on the i n t e r a c t i o n between 27 d i f f e r e n t l e v e l s of the molecule.  The m i x i n g  of d i f f e r e n t excited states  by c r y s t a l f o r c e s causes a s i g n i f i c a n t r e d i s t r i b u t i o n of i n t e n s i t y o f a b s o r p t i o n a l o n g two  symmetry axes o f the c r y s t a l .  t r e a t m e n t of p u r e c r y s t a l s p e c t r a , second o r d e r  In analogy with  the  e f f e c t s i n mixed c r y s t a l s  are e x p e c t e d t o o c c u r s i n c e t h e i n t e r a c t i o n t a k e s p l a c e between d i f f e r e n t 31 e x c i t e d s t a t e s of the guest and h o s t . Choudhury and Ganguly examined t h e p o l a r i z e d a b s o r p t i o n spectrum o f t e t r a c e n e i n anthracene.' The e x p e r i i  mentally  determined p o l a r i z a t i o n r a t i o I ^ I  o r i e n t e d gas v a l u e  ;  7.8:1  a  o f 1.9:1  indicates appreciable  compared w i t h  i n t e r a c t i o n . The  the  theory  e l e c t r o n i c s p e c t r a of mixed c r y s t a l s i n the d i p o l e - d i p o l e a p p r o x i m a t i o n  of has  -  -  18  32 been a p p l i e d t o a number o f systems. G.  The Theory o f M o l e c u l a r V i b r a t i o n s 33 The c l a s s i c a l t r e a t m e n t  of the v i b r a t i o n s o f p o l y a t o m i c m o l e c u l e s  34 '  i n v o l v e s s e t t i n g up e x p r e s s i o n s f o r t h e p o t e n t i a l and k i n e t i c e n e r g i e s o f the molecules  i n terms o f a s u i t a b l e c o o r d i n a t e system o f t h e atoms.  The  e x p r e s s i o n s f o r t h e k i n e t i c and p o t e n t i a l energy a r e used t o f o r m u l a t e t h e wave e q u a t i o n which i s t h e n s o l v e d f o r the v i b r a t i o n s , r o t a t i o n s , translations.  In the Born-Oppenheimer a p p r o x i m a t i o n  n u c l e a r motions are s e p a r a t e d .  The k i n e t i c energy o f t h e m o l e c u l e m  ±  a  L  (-  d  T  - )  +  r  a  t o be  determined.  i s g i v e n by  where (x, ,x., , x„ ) are t h e d i s p l a c e m e n t s ^ l a ' • 2a' 3cr m  (~ ~ d  )  of the  (-^-)  +  ]  (1.27)  a t h atom from e q u i l i b r i u m . n  i s t h e mass o f the atom and N i s the number o f atoms i n the  In terms o f mass weighted  and  F u r t h e r , i t i s assumed t h a t t h e e l e c t r o n i c  energy i s known and o n l y the n u c l e a r m o t i o n s . a r e  21 =J  the e l e c t r o n i c  and  c a r t e s i a n coordinates (q^, q  2 ?  ;  molecule,  I j ; • • - l ^ ) defined  by  q  1  = Vm^  q  4  = vV  x , n  q  2  =  x^,  q  3  =• vfiu, x ^ ,  x ...  2  1 2  t h e k i n e t i c energy i s 3N 2T = . I. q 1=1 i  (1 .28)  l  In m a t r i x n o t a t i o n 2T - q  +  E  q where q i s a column m a t r i x o f t h e q^ and E  i s the i d e n t i t y m a t r i x . For s m a l l d i s p l a c e m e n t s the p o t e n t i a l energy may  be expressed  as a  - 19  -  power s e r i e s e x p a n s i o n o f the form  3 N  2V  = 2V  o  +2  3 ? (_!• ) q. + E °q. o i . - . i i>J=l 3  V  E . , 1=1  v  n  n  9V (^J! ) q.q. + 9q. q. ' o i j i J 2  n  n  (1.29)  3N + 2 ^ . , 1=1  = 2V o  3Nf.q. + • E i i . . i i,J=l n  f . . q . q . + ... 11 l l n  (1.30)  n  J  J  By c h o o s i n g t h e p o t e n t i a l energy o f t h e e q u i l i b r i u m c o n f i g u r a t i o n o f t h e atoms t o be z e r o , and n o t i n g t h a t a t t h e p o t e n t i a l energy minimum  9V  (_L )  9q. o i  = f. = o  (1.31)  l  n  t h e n f o r s m a l l a m p l i t u d e s o f v i b r a t i o n , t h e h i g h e r terms may be neglectedand t h e f i n a l e x p r e s s i o n f o r t h e p o t e n t i a l energy i s g i v e n by the f i r s t non-zero term.  3N _2 3N 2V - E f \ ) q.q. = E f..q.q. . . 9q.9q. o i i . . 11 i 1 i,j=l i j • i , j• . v  n  n  n  H  (1.32)  n  J  J  J  The dependence o f t h e p o t e n t i a l energy on o n l y t h e q u a d r a t i c terms i m p l i e s t h a t t h e v i b r a t i o n a l m o t i o n i s harmonic. c o n s t a n t s a r e d e f i n e d by  In t h i s approximation the f o r c e '  .  2 f. . = (I \ •) 13 ^ q ^ ^ o  In m a t r i x n o t a t i o n t h e p o t e n t i a l energy i s 2V = q symmetric m a t r i x w i t h independent terms.  v  +  (1.33) J  f q where f i s a  f j ^ . The f o r c e c o n s t a n t m a t r i x f,.has  -|(N) (N+l)  - 20 -  A system o f p a r t i c l e s i n m o t i o n must obey Lagrange's  equations.  In  terms o f mass w e i g h t e d c o o r d i n a t e s , t h e s e a r e  d 3T -TT- ——— dt 3q  +  3V  -r— 3q  = 0  (1-34) «• J  S u b s t i t u t i o n o f t h e e x p r e s s i o n s f o r T and V y i e l d s 3N e q u a t i o n s  q. J  +  3N £ f..q. = 0 i=l 1 3  (1.35)  1  T h i s s e t o f 3N s i m u l t a n e o u s second-order  l i n e a r d i f f e r e n t i a l e q u a t i o n s has  s o l u t i o n s o f t h e form  q  i  = A.cos(A" t +  e)  (1.36)  where A^ i s t h e a m p l i t u d e o f t h e v i b r a t i o n , A a.frequency phase f a c t o r .  f a c t o r and e a  S u b s t i t u t i o n of t h i s s o l u t i o n into the d i f f e r e n t i a l  equations  r e s u l t s i n a s e t o f e q u a t i o n s i n t h e unknown a m p l i t u d e s A^  3N £ i-1  or i n m a t r i x n o t a t i o n The t r i v i a l s o l u t i o n s  ( f . . - 6.. A.)A. = 0 iJ iJ J i  ( f - E A)A = 0 f o r which A. = 0 c o r r e s p o n d t o t r a n s l a t i o n s and  r o t a t i o n s o f t h e m o l e c u l e as a whole. of  (1.37)  Non-zero s o l u t i o n s o c c u r f o r v a l u e s  A_. which s a t i s f y t h e d e t e r m i n a n t a l o r s e c u l a r  |f - E A | - 0  equation  (1.38)  -  Development o f t h e e q u a t i o n s  21  -  i n mass weighted  Cartesian coordinates  i s f a i r l y s i m p l e , b u t i t i s u s u a l l y n o t s o l v e d i n t h i s form. possible values of  X., t h e s i x v a l u e s c o r r e s p o n d i n g  Among t h e 3 N  t o t h e t r a n s l a t i o n s and  r o t a t i o n s a r e z e r o , and more i m p o r t a n t , t h e f o r c e c o n s t a n t s e x p r e s s e d i n t h i s system l a c k g e n e r a l i t y s i n c e t h e y a r e a p p l i c a b l e t o a s p e c i f i c and a r e not t r a n s f e r a b l e among s i m i l a r m o l e c u l e s .  molecule  I t i s therefore desirable  t o d e f i n e i n t e r n a l c o o r d i n a t e s i n a way such t h a t t h e y d e s c r i b e t h e motions o f t h e atoms, and a r e independent o f t h e t r a n s l a t i o n s and r o t a t i o n s o f t h e molecule  as a whole.  The f o r c e c o n s t a n t s s h o u l d a l s o be t r a n s f e r a b l e among  s i m i l a r m o l e c u l e s h a v i n g s i m i l a r c h e m i c a l bonds. A s e t o f i n t e r n a l c o o r d i n a t e s i n terms o f bond s t r e t c h i n g ,  valence-angle 33  bending,  out-of^plane bending,  and bond t o r s i o n has been d e f i n e d .  i s u s u a l l y r e f e r r e d t o as v a l e n c e c o o r d i n a t e s .  This set  From a diagram o f t h e  m o l e c u l e , t h e p o t e n t i a l energy can be w r i t t e n down i n terms o f t h e i n t e r n a l v a l e n c e c o o r d i n a t e s (R^) and t h e k i n e t i c energy i n terms o f C a r t e s i a n coordinates.  U s i n g t h e t r a n s f o r m a t i o n from i n t e r n a l c o o r d i n a t e s t o  Cartesian coordinates  R  =  (1.39)  Bx  t h e k i n e t i c energy c a n be e x p r e s s e d  i n terms o f i n t e r n a l c o o r d i n a t e s .  elements o f t h e B-matrix a r e r e a d i l y o b t a i n e d by t h e W i l s o n technique.  The  s-vector  I n m a t r i x n o t a t i o n , t h e k i n e t i c and p o t e n t i a l e n e r g i e s i n  i n t e r n a l coordinates are  . 21'  =  1  B 5 +  1  M F,M2 2  . B  -  1  R  =  R ^ G ^ R  (1.40)  -  22 -  2V = R F R  (1-41)  +  where M i s a d i a g o n a l m a t r i x made up o f t h e masses o f t h e atoms.  As b e f o r e ,  a p p l i c a t i o n o f Lagrange's e q u a t i o n and s o l u t i o n s o f t h e form  R  = A  i  i  cos (At + e)  (1.42)  r e s u l t s i n the s e c u l a r determinant  GF - AEl = 0  The 3N - 6 v a l u e s o f  (1.43)  A . y i e l d 3N - 6 i n t e r n a l v i b r a t i o n s o f t h e m o l e c u l e . J  I n i n t e r n a l c o o r d i n a t e s , t h e p o t e n t i a l and k i n e t i c energy m a t r i c e s c o n t a i n c r o s s terms which c o m p l i c a t e t h e v i b r a t i o n a l p r o b l e m .  However, t h e r e  i s a m a t r i x L w h i c h t r a n s f o r m s i n t e r n a l c o o r d i n a t e s t o normal c o o r d i n a t e s i = 1,2,3, ..3N-6 i n which a l l t h e c r o s s terms i n t h e p o t e n t i a l and k i n e t i c energy e x p r e s s i o n s a r e e l i m i n a t e d .  In matrix n o t a t i o n , the trans-  f o r m a t i o n i s d e f i n e d as  R = L Q  (1.44)  and must s a t i s f y t h e c o n d i t i o n s 1  2  =  R G R = Q L G L Q = QE Q +  - 1  +  +  _ 1  +  and  2y = R F -R = Q L F L Q = Q A  Therefore  L G  and  L F L =  +  +  +  _ 1  +  L = E A  +  +  Q  (1.45)  (1.46)  (1-47) (1 -48)  - 23 -  where E i s t h e i d e n t i t y m a t r i x and A  a diagonal matrix.  The s i g n i f i c a n c e o f each normal c o o r d i n a t e  i s that i t describes a  e e r t a i n change i n t h e arrangement o f t h e atoms o f a m o l e c u l e w i t h r e s p e c t t o each o t h e r .  Further, corresponding  t o each normal c o o r d i n a t e t h e r e i s  a s o l u t i o n o f t h e s e c u l a r e q u a t i o n such t h a t • t h e atoms move w i t h t h e same frequency  and phase b u t d i f f e r i n g a m p l i t u d e s .  That i s , a l l t h e atoms o f a  m o l e c u l e r e a c h t h e i r maximum or minimum d i s p l a c e m e n t  a t . t h e same t i m e .  These c h a r a c t e r i s t i c s d e f i n e a normal mode o f v i b r a t i o n . frequency  i s known as a fundamental f r e q u e n c y  I t s associated  of the molecule.  A normal mode i s e a s i l y v i s u a l i z e d by e x p r e s s i n g t h e normal i n terms o f C a r t e s i a n d i s p l a c e m e n t  c o o r d i n a t e s by t h e t r a n s f o r m a t i o n  3 N Q. = I .I l . . . j = l a=l The c o e f f i c i e n t s a.,  coordinates  a.. x. lia ia  (1.49)  d e s c r i b e the change o f t h e C a r t e s i a n c o o r d i n a t e s x.  per u n i t change o f normal c o o r d i n a t e  a" ' = 1  ?x. - i 3  Q  (1.50)  a  i  An a p p r o x i m a t e d e s c r i p t i o n of- t h e normal modes i s d e r i v e d by e q u a t i n g i t w i t h t h a t v a l e n c e c o o r d i n a t e which makes t h e l a r g e s t c o n t r i b u t i o n t o the p o t e n t i a l energy.  I n v a l e n c e c o o r d i n a t e s t h e p o t e n t i a l energy o f a  normal mode i s ; A. =  3N-6 E  3N-6 E  F: . , L.. L. , . ,  (1.51)  24  The meaning o f each L.. o f t h e L - m a t r i x i s t h e change o f v a l e n c e  coordinate  R p e r u n i t change o f normal c o o r d i n a t e Q 3R.  V=3QT  The  C 1  l a r g e s t terms i n t h e p o t e n t i a l energy m a t r i x F a r e t h e d i a g o n a l  '  5 2 )  terms.  In t h i s case t h e l a r g e s t term i n X. i s t h e r e s u l t o f a l a r g e f o r c e c o n s t a n t (f • n v  •  -  3^V 2 2 -^K—?) o r a l a r g e L - m a t r i x element (L.. = (•--— ) . The v a l e n c e 9R ^ ^ n ^9Q ^ &  i  coordina/te R i s chosen as t h e approximate d e s c r i p t i o n o f t h e mode.  The The  I n t e n s i t y o f I n f r a r e d Bands L - m a t r i x i s u s e f u l i n a c c o u n t i n g f o r t h e i n t e n s i t y o f a normal mode  i n terms o f i n t e r n a l c o o r d i n a t e s and thus p r o v i d e s a more e a s i l y v i s u a l i z e d 33 e x p l a n a t i o n f o r t h e i n t e n s i t y o f a a b s o r p t i o n band. accessible integrated intensity  The e x p e r i m e n t a l l y  c o e f f i c i e n t i f we d e f i n e S t o be p r o p o r t i o n a l  t o t h e square o f t h e t r a n s i t i o n d i p o l e moment f o r a v i b r a t i o n i s ) P(Q) X j C Q - W j ]  For s m a l l d i s p l a c e m e n t s series  t h e d i p o l e moment o p e r a t o r i s approximated  by t h e  expansion  u(Q)  3u If —i— 3Q.  (1-53)  2  =  3N-6 .. £ u  +  3N-6 E  ' (±)(L  +  ...  (1.54)  i s assumed t o be constant, over t h e whole a m p l i t u d e o f t h e v i b r a t i o n . .  G\, t h e e x p r e s s i o n f o r S_. becomes  25  S.  -ij^.n.  X^Q^dQ.]  (|-)  2  (1.55)  2  x a r e assumed t o be  T h i s can be e v a l u a t e d i f t h e v i b r a t i o n a l w a v e f u n c t i o n s 33 harmonic o s c i l l a t o r w a v e f u n c t i o n s .  i  The f i n a l r e s u l t  3c  90. o  where c i s t h e v e l o c i t y o f l i g h t . u n d e r s t o o d by d e v e l o p i n g  4^—  is  Now t h e o r i g i n o f t h e i n t e n s i t y can be  i n terms o f i n t e r n a l c o o r d i n a t e s  j  ai,'  3 N  3Q. j  "  x  ~  6  . . 1=1  a,, 3R. l  9 R  3Qj x  3N-6 "  . . 1=1  « 3R. j  L  ij  U  J  -  5 / J  9y A l l 3N-6 o f t h e q u a n t i t i e s  ^Q—  y i e l d a s e t o f l i n e a r homogeneous  equations  9y J i n t h e unknowns . The s o l u t i o n o f the e q u a t i o n s g i v e s t h e l a r g e s t 3y term c o n t r i b u t i n g t o and thus t h e source o f t h e i n t e n s i t y o f t h e 3Q. i n f r a r e d a b s o r p t i o n band. 1  - r r r —  I.  Determination o f Force  Constants  I n g e n e r a l , i t i s n o t p o s s i b l e t o determine  the f o r c e constants  ( F - m a t r i x ) from e x p e r i m e n t a l l y observed fundamental 3N-6 e q u a t i o n s which form t h e s e c u l a r e q u a t i o n have  frequencies s i n c e the y(3N-6) (3N-6+1)  unknowns. Three methods o f a t t a c k commonly used t o o b t a i n f o r c e c o n s t a n t s 33 are; '  (a) t h e use o f f r e q u e n c i e s from i s o t o p i c a l l y s u b s t i t u t e d m o l e c u l e s ,  (b) the use o f symmetry t o f a c t o r t h e s e c u l a r e q u a t i o n , and (c) the use o f simplified force f i e l d s . The f o r c e c o n s t a n t s depend on t h e e l e c t r o n i c s t r u c t u r e o f a m o l e c u l e which i n t u r n i n v o l v e s t h e charges and c o n f i g u r a t i o n o f t h e n u c l e i b u t not  - 26 t h e masses.  -  Presumably, t h e i s o t o p i c s u b s t i t u t i o n o f one o r more atoms  does not a l t e r the e l e c t r o n i c s t r u c t u r e and t h e r e f o r e the change i n f o r c e c o n s t a n t s w i l l be n e g l i g i b l e .  The k i n e t i c energy does depend on  masses so t h a t i s o t o p i c s u b s t i t u t i o n a l t e r s the G-matrix and the f r e q u e n c i e s .  consequently  The most f a v o u r a b l e mass change i s a c h i e v e d by r e p l a c i n g  hydrogen by d e u t e r i u m . a d d i t i o n a l equations The  the  The  i n the  a l t e r e d f r e q u e n c i e s and G-matrix elements p r o v i d e — (3N-6)(3N-6+1) f o r c e c o n s t a n t s .  symmetry o f a m o l e c u l e  o f t e n makes i t p o s s i b l e t o u t i l i z e  t h e o r e t i c a l methods t o f a c t o r i z e b o t h the G and  group  F m a t r i c e s and hence the  33 s e c u l a r e q u a t i o n i n t o b l o c k form.  Each b l o c k b e l o n g s t o a d i f f e r e n t  i r r e d u c i b l e r e p r e s e n t a t i o n o f t h e p o i n t group o f t h e m o l e c u l e  so t h a t t h e r e  a r e no o f f d i a g o n a l terms c o n n e c t i n g d i f f e r e n t symmetry b l o c k s . symmetrized s e c u l a r e q u a t i o n each b l o c k may  be t r e a t e d as a  In the  separate  problem. A number o f a p p r o x i m a t i o n s force f i e l d .  The  a r e used t o d e s c r i b e the g e n e r a l q u a d r a t i c  c e n t r a l f o r c e f i e l d i s one o f the s i m p l e s t a p p r o x i m a t i o n s .  used t o reduce the number o f independent f o r c e c o n s t a n t s .  A l l the  internal  c o o r d i n a t e s are d e f i n e d as d i s t a n c e s between p a i r s o f atoms b o t h bonded and non-bonded, and each p a i r o f atoms i s connected by a f o r c e . force f i e l d yields a  The  central  d i a g o n a l p o t e n t i a l energy m a t r i x , but has been  u n s a t i s f a c t o r y i n a p p l i c a t i o n t o a l l but the s i m p l e s t The v a l e n c e f o r c e f i e l d chemical p o i n t of view.  i s an a p p r o x i m a t i o n  molecules.  most c o m p a t i b l e  w i t h the  I t assumes t h a t the p o t e n t i a l energy o f a  can be s a t i s f a c t o r i l y d e s c r i b e d i n terms o f changes i n l e n g t h o f bonds and c h a n g e s . i n , a n g l e s  between c h e m i c a l bonds.  molecule  chemical  The number of..force  c o n s t a n t s i s u s u a l l y l e s s than the number o f f r e q u e n c i e s and they can always be d e t e r m i n e d from t h e s e c u l a r e q u a t i o n .  However, the n e g l e c t o f terms o f f  - 27  -  t h e d i a g o n a l i n the F - m a t r i x r e n d e r s the a p p r o x i m a t i o n t o o i n a c c u r a t e t o be u s e f u l i n most c a s e s . An a p p r o x i m a t i o n which i s s i m p l e r t h a n t h e g e n e r a l f o r c e f i e l d combines the f e a t u r e s of b o t h the c e n t r a l and v a l e n c e f o r c e f i e l d  and  i s known  35 as t h e U r e y - B r a d l e y f o r c e f i e l d ,  I t has terms  i n v o l v i n g bond l e n g t h  changes and a n g l e bends, and i n c l u d e s i n t e r a c t i o n terms between non-bonded atoms as d i a g o n a l e n t r i e s i n the F m a t r i x . i n a Urey-Bradley force f i e l d s i m p l i f y i n g the problem Urey-Bradley force f i e l d transformation  i s l e s s than  considerably.  ^(3N-6)(3N-6+1)  I n a normal  thereby  c o o r d i n a t e a n a l y s i s the  i s i n c o r p o r a t e d i n t o t h e s e c u l a r e q u a t i o n by t h e  1  F... = jk  or  The number o f f o r c e c o n s t a n t s  z  1  1... *. jkl 1  (1.58)  v  1  i n matrix notation  Z$  (1-59)  where Z i s a c o n s t r a i n t m a t r i x and |_ the U r e y - B r a d l e y f o r c e c o n s t a n t s .  Chapter 2 M a t e r i a l s and E x p e r i m e n t a l  A.  Methods  P u r i f i c a t i o n and Syntheses o f M a t e r i a l s P r e l i m i n a r y e x p e r i m e n t s c a r r i e d out on Eastman Kodak White L a b e l  f l u o r e n e i n d i c a t e d t h a t s u b l i m a t i o n reduced but d i d not e l i m i n a t e peaks i n o  o  t h e s o l u t i o n a b s o r p t i o n spectrum at 3470 A and phenanthrene and  c a r b a z o l e , r e s p e c t i v e l y ) and  3380 A ( p o s s i b l y due  to  t h a t zone r e f i n i n g reduced  o  but d i d not e l i m i n a t e the peak at 3200.A. was  p u r i f i e d i n the f o l l o w i n g way.  Therefore,  Fluorene  was  commercial  fluorene  treated with maleic  anhydride  t o remove t h e a n t h r a c e n e a c c o r d i n g t o a m o d i f i e d p r o c e d u r e p r e s c r i b e d f o r removing a n t h r a c e n e from p h e n a n t h r e n e . ^ 0  c a r b a z o l e , was e t h e r , and  mixture  was  evaporating  removed by d i s s o l v i n g the r e s u l t i n g m a t e r i a l i n p e t r o l e u m  shaking  concentrated  the s o l u t i o n s e v e r a l t i m e s w i t h s m a l l q u a n t i t i e s o f  s u l p h u r i c a c i d u n t i l the a c i d l a y e r no l o n g e r d i s c o l o u r e d . washed w i t h d i s t i l l e d the s o l v e n t .  t h e f l u o r e n e from any d u r i n g the m a l e i c on a 200 gm  A second i m p u r i t y , p o s s i b l y  water and the f l u o r e n e r e c o v e r e d  T h i s was  f o l l o w e d by slow s u b l i m a t i o n t o  i n v o l a t i l e i m p u r i t i e s t h a t may  anhydride treatment.  A 2 gm  s i l i c a g e l column (25" x 1 1/4"  eluent, successive  The  by separate  have been added  sample was  next chromatographed  dia.) with petroleum ether  1.00 ml f r a c t i o n s b e i n g checked f o r an i m p u r i t y  as  absorption  o  peak at 3200 A i n a 5 cm c e l l .  S u f f i c i e n t i m p u r i t y was  c o l l e c t e d before  the  - 29  f l u o r e n e was  -  e l u t e d t o c o n f i r m i t s i d e n t i t y as b e n z [ f ] i n d a n .  stage o f p u r i f i c a t i o n was  37  The  zone r e f i n i n g , the f l u o r e n e u n d e r g o i n g 86  last passes.  o  The  f i n a l sample was  o p t i c a l l y c l e a r t o n e a r l y 3000 A; t h e r e were no o  a b s o r p t i o n l i n e s above 3052 A i n a 1 mm  t h i c k sample h e l d at about  a l t h o u g h a weak f l u o r e s c e n c e w i t h a doubled o r i g i n at 29,519 and persisted. The  The  i d e n t i t y o f t h i s r e s i d u a l i m p u r i t y was  impurity separated  ( i ) The  29,505 cm  *  not e s t a b l i s h e d .  from f l u o r e n e by chromatography was  b e n z [ f ] i n d a n from t h e f o l l o w i n g e v i d e n c e :  10°K  i m p u r i t y was  shown t o  be  e l u t e d from  37 t h e chromatography column b e f o r e f l u o r e n e  . ( i i ) F o l l o w i n g two  recrystal-  l i z a t i o n s from n-hexane, the s o l u t i o n a b s o r p t i o n spectrum agreed w i t h t h a t 37 of benz[f]indan  , ( i i i ) The mass spectrum showed the p a r e n t mass peak a t  ( i v ) A n a l y s i s found C, 92.02%; H, 7.79% H, 7.20%.  Thus the i m p u r i t y was  w h i l e b e n z [ f ] i n d a n r e q u i r e s C,  a hydrocarbon of molecular  the u l t r a - v i o l e t a b s o r p t i o n spectrum i n d i c a t i n g ring.  The  168.  92.80%;  weight 168  with  the p r e s e n c e o f a n a p h t h a l e n e  t h r e e s t r u c t u r e s o f F i g . 1 are c o n s i s t e n t w i t h t h i s d a t a .  Again  38 i t i s known  t h a t I and  I I I a r e c o l o u r l e s s s o l i d s m e l t i n g at 94°C and  64°C r e s p e c t i v e l y , w h i l e I I i s a l i q u i d a t room t e m p e r a t u r e . t e s t s were c a r r i e d  A l l t h e above  out on t h e s m a l l amount o f i m p u r i t y ( i n i t i a l l y about 20  s e p a r a t e d by chromatography.  A f a i n t y e l l o w c o l o u r t h a t had  up i n the sample ( p r o b a b l y by a e r i a l o x i d a t i o n ) was  mg)  slowly b u i l t  removed by  sublimation  i n a stream o f n i t r o g e n e n t r a i n e r gas when the m a t e r i a l m e l t e d over the range 86-91°C; t h e r e was  not enough m a t e r i a l f o r f u r t h e r p u r i f i c a t i o n  A h i g h r e s o l u t i o n n.m.r. spectrum ( F i g . 2) was  recorded  (impure) m a t e r i a l where the p r e s e n c e o f groups o f two protons  on the  and f o u r  remaining equivalent  on the a r o m a t i c r i n g , and two and f o u r e q u i v a l e n t p r o t o n s  a l k y l s i d e c h a i n were r e v e a l e d .  steps.  on  These f e a t u r e s were c o n s i s t e n t w i t h  the either  - 30 -  s t r u c t u r e I o r I I I , but t h e m e l t i n g p o i n t i n d i c a t e d t h a t s t r u c t u r e I was correct.  Thus we have shown t h a t b e n z [ f ] i n d a n  f l u o r e n e , present  i s a common i m p u r i t y i n  i n our samples (from Eastman Kodak and Matheson, Coleman 37  and  B e l l ) as w e l l as i n Johnson's. The commercial m a t e r i a l showed a s h a r p , b - p o l a r i z e d a b s o r p t i o n a t  32,789 cm * i n an ab f a c e which was a l t o g e t h e r absent i n t h e s y n t h e t i c sample; t h i s marks t h e p r e s e n c e o f y e t a n o t h e r unknown i m p u r i t y i n commercial f l u o r e n e .  y  I  Fig. 1  II  P o s s i b l e s t r u c t u r e s f o r t h e i m p u r i t y g i v i n g t h e weak a b s o r p t i o n a t 3200 A.  Fluorene essentially  I benz[f]indan;  I I benz[e]indan;  was a l s o p r e p a r e d from b e n z i l i c a c i d .  I I I 2,3-dihydrophenalene.  The s y n t h e s i s was  ' 39 t h e second method f o l l o w e d by Kanda e_t a l _ . except t h a t , i n  the l a s t step, fluorenbne Wolff-Kishner  o  III  reaction.  o  40  was reduced t o f l u o r e n e by a m o d i f i c a t i o n o f t h e 0  A l t h o u g h t h e r e were no i m p u r i t y peaks a t 3200 A,  3380 A o r 3470 A, t h i s s y n t h e t i c m a t e r i a l was contaminated w i t h a n t h r a c e n e w h i c h was removed by t r e a t m e n t w i t h m a l e i c a n h y d r i d e .  Following  chromato-  graphy and zone r e f i n i n g , t h e f i n a l s y n t h e t i c m a t e r i a l showed no a b s o r p t i o n  H(l,3) H (5,6,7,8.)  8  Fig. 2  NMR  spectrum o f b e n z [ f ] i n d a n .  9  I  -  32 o  o r f l u o r e s c e n c e o r i g i n s above 3052 A i n a 1.5 mm 10°K.  However, even t h i s sample was  s i n c e a t low t e m p e r a t u r e t h e r e was  not c o m p l e t e l y  and  pure s p e c t r o s c o p i c a l l y  as f l u o r e n e .  subjected to e s s e n t i a l l y The  chromatography was  the sample passed 46 times through a zone r e f i n e r .  t i o n l i n e s appeared i n a 2 mm 41  and  i s expected t o phosphoresce b l u e .  l a b e l b i p h e n y l was  same p u r i f i c a t i o n p r o c e d u r e  (be f a c e ) a t  a v e r y f a i n t green phosphorescence  s o l i d f l u o r e n e , i f i t phosphoresces at a l l , Eastman Kodak w h i t e  thickness  eliminated  No i m p u r i t y absorp-  t h i c k sample a t about 10°K;  r e n e f l u o r e s c e n c e , - a l t h o u g h v e r y weak, was  the  however,  d e t e c t e d on a  phenanth.  photographic  p l a t e exposed f o r 2 h r . White l a b e l c a r b a z o l e s u p p l i e d by Eastman Kodak was cene by treatment  w i t h maleic anhydride.  f o l l o w i n g a technique e t h e r as an e l u e n t . was  f r e e d from a n t h r a -  The sample was 42  d e v e l o p e d by Sangster  then chromatographed  on s i l i c a g e l u s i n g p e t r o l e u m  The b r i g h t b l u e f l u o r e s c e n c e o f t h e s t a r t i n g m a t e r i a l  r e p l a c e d by a deep v i o l e t f l u o r e s c e n c e i n the p u r i f i e d Eastman Kodak w h i t e  l a b e l d i b e n z o t h i o p h e n e was  sample.  used a f t e r undergoing  204 p a s s e s i n a zone r e f i n e r . 43 Perdeuterated  d i b e n z o t h i o p h e n e was  s u p p l i e d by Merck, Sharp and Dohm.  synthesized  from biphenyl-d-^Q  F i n a l p u r i f i c a t i o n of the p r o d u c t  was  a c h i e v e d by s u b l i m a t i o n i n an a p p a r a t u s which c o n s i s t e d o f a p y r e x tube connected t o a n i t r o g e n c y l i n d e r and t h a t a t e m p e r a t u r e g r a d i e n t was The  sample was  i n s e r t e d i n t o a furnace constructed  s e t up along the h o r i z o n t a l p y r e x  so  tube.  p l a c e d i n the h o t t e s t p a r t o f the tube, and a g e n t l e f l o w o f  n i t r o g e n d e p o s i t e d the m a t e r i a l s at v a r y i n g d i s t a n c e s a l o n g the tube a c c o r d i n g t o t h e i r r a t e and t e m p e r a t u r e o f s u b l i m a t i o n . i m p u r i t y was  A l i g h t blue f l u o r e s c i n g  d e p o s i t e d i n the c o o l e s t p a r t o f the tube.  a n a l y s i s showed t h a t the f i n a l p r o d u c t  c o n t a i n e d about  Mass s p e c t r a l 1 7  %  dibenzothiophene-" ^ > <> 1  d  7  - 33 S p e c t r o q u a l i t y c y c l o h e x a n e ( B r i t i s h Drug Houses), benzene  (Fischer)  and n-heptane (Matheson, Coleman and B e l l ) were used w i t h o u t f u r t h e r purification.  B.  P r e p a r a t i o n o f Samples A l l c r y s t a l s were grown i n evacuated p y r e x tubes from the m e l t by 44  s l o w l y l o w e r i n g the sample through a Bridgman  furnace.  Pure c r y s t a l s  o f c a r b a z o l e , f l u o r e n e , d i b e n z o t h i o p h e n e - h g , and d i b e n z o t h i o p h e n e - d g were used f o r i n f r a r e d and Raman s t u d i e s .  Mixed c r y s t a l s systems i n which t h e  -2 g u e s t / h o s t c o n c e n t r a t i o n s v a r i e d from about 10  -3 M/M  t o 10 : M/M  were used  f o r a b s o r p t i o n and luminescence e x p e r i m e n t s . . The guest m a t e r i a l s were c a r b a z o l e , d i b e n z o t h i o p h e n e - h , d i b e n z o t h i o p h e n e - d , and b e n z [ f ] i n d a n ; the D  Q  o  o  h o s t m a t e r i a l s were f l u o r e n e , b i p h e n y l , and  hexamethylbenzene.  S t r a i n - f r e e , s i n g l e c r y s t a l p o r t i o n s o f an i n g o t were s e l e c t e d by examining t h e sample f o r complete, u n i f o r m e x t i n c t i o n under a p o l a r i z i n g microscope.  The a p p r o p r i a t e c r y s t a l f a c e was  i d e n t i f i e d by c o n o s c o p i c  e x a m i n a t i o n u s i n g o p t i c a l d a t a f o r f l u o r e n e and b i p h e n y l summarized by 45 Winchell.  The c o n o s c o p i c f i g u r e s shown by c a r b a z o l e a r e t h e same as  t h o s e o f f l u o r e n e a l t h o u g h the changed naming o f the c r y s t a l axes as i l l u s t r a t e d i n F i g . 6 and F i g . 8 s h o u l d be n o t e d .  The o p t i c a l  properties  o f d i b e n z o t h i o p h e n e were e s t a b l i s h e d on a sample f o r which t h e c r y s t a l axes  (a_,b_,c) were known from X-ray a n a l y s i s .  The r e s u l t s o f t h i s  a t i o n a r e i n c l u d e d i n t h e s e c t i o n on c r y s t a l s t r u c t u r e s and  examin-  optical  properties. A f t e r the d e s i r e d c r y s t a l f a c e was p r e p a r e d by p l a n i n g w i t h a r a z o r b l a d e .  i d e n t i f i e d , i t was  carefully  N e x t , t h e sample was p l a c e d on  - 34 -  •I • i  the p r e p a r e d f a c e i n a b r a s s r i n g w i t h the d e s i r e d c r y s t a l t h i c k n e s s and packed w i t h P l a s t e r o f P a r i s .  When t h e p l a s t e r had s e t , t h e c r y s t a l  ground on f i n e emery, paper t o t h e t h i c k n e s s o f t h e b r a s s r i n g . samples 0.15  mm  was  With c a r e ,  t h i c k were p r e p a r e d but r e q u i r e d f u r t h e r p o l i s h i n g i n o r d e r  t o be s u i t a b l e f o r i n f r a r e d e x p e r i m e n t s .  F i n a l l y , to prevent l i g h t losses  from s c a t t e r i n g and t o a c h i e v e v e r y t h i n samples ( < 0.1 mm),  the s u r f a c e s  were p o l i s h e d w i t h a s u i t a b l e s o l v e n t such as a c e t o n e , e t h a n o l , e t c . on a b r a s s b l o c k wrapped w i t h  soft tissue  paper.  C. - C r y o s t a t s The b u l k o f t h e a b s o r p t i o n and luminescence  experiments  were c a r r i e d out 46  u s i n g a l i q u i d h e l i u m c r y o s t a t o f the s t a n d a r d D u e r i g and Madorm a i n l y because i t s d i s m a n t l i n g and assembly were a c c o m p l i s h e d The  sample was  c o o l e d by c o n d u c t i n g away i t s t h e r m a l energy  h e l i u m t h r o u g h GE 7031  w i t h ease.  to  cement and a s h o r t l e n g t h o f copper.  design  liquid  The  temperature  o f t h e c r y s t a l d i d depend on the i n c i d e n t l i g h t i n t e n s i t y and was t o be about 15°K.  The c a p a c i t y o f t h e h e l i u m r e s e r v o i r was  h o l d enough l i q u i d h e l i u m to l a s t 6-8  estimated  s u f f i c i e n t to  hours.  A l i q u i d h e l i u m c r y o s t a t somewhat m o d i f i e d f o l l o w i n g t h e s u g g e s t i o n o f 47 Roberts  i n which  the sample was  c o o l e d by h e l i u m heat exchange gas i n  c o n t a c t w i t h the l i q u i d h e l i u m c o n t a i n e r had two main advantages. experiment  c o u l d be conducted  over a range o f t e m p e r a t u r e s , and samples c o u l d  be s u p p o r t e d l o o s e l y i n such a way t h e c o o l i n g and warming p r o c e s s .  t h a t a minimum o f s t r a i n was C o n s i d e r a b l e d i f f i c u l t y was  involved i n experienced  i n a c h i e v i n g vacuum t i g h t s e a l s u s i n g indium 0 - r i n g s between t h e windows and t h e metal frame.  An  silica  The most s u c c e s s f u l procedure r e q u i r e d c l e a n i n g  -  35 -  the m e t a l s u r f a c e s w i t h s t e e l wool and t h e i n d i u m O - r i n g s w i t h s i l v e r s o l d e r flux  (Stay B r i t e ) .  B e f o r e each e x p e r i m e n t , a l l vacuum t i g h t s e a l s were  checked w i t h a B a l z e r s l e a k d e t e c t o r u s i n g Freon 12 as a t e s t g a s .  D.  C a l i b r a t i o n o f Gas Thermometer The t e m p e r a t u r e o f t h e samples was e s t i m a t e d  t o w i t h i n about a degree  d u r i n g t h e c o o l i n g and warming up p r o c e s s by m o n i t o r i n g  the pressure o f  48 t h e h e l i u m h e a t exchange gas i n t h e sample chamber.  A s c h e m a t i c drawing  o f t h e gas thermometer i s d i s p l a y e d i n F i g . 3.  connecting tube  V  sample chamber  pressure gauge Fig, 3  Helium gas thermometer  T h i s d i s c u s s i o n assumes t h a t h e l i u m behaves i d e a l l y and t h a t t h e volume o f t h e connecting ignored.  l i n e s which s u f f e r a temperature g r a d i e n t i s s m a l l enough t o be At f i l l i n g ,  w h i l e V" i s a t P 2  2  and T  and V" a r e a t 2  and T^; i n u s e ,  i s at  and T^  Then a t T ,  2 >  P (V 1  1  RT,  + v) 2  = n  (2.1)  -  36 -  and a t T ,  P V  2  2  RTj  x  >  '  RT  2  =  —  (-)  n _ x  2  2  whsre n i s t h e t o t a l number o f moles o f h e l i u m i n the number o f moles o f h e l i u m i n V" a t T^.  l  o r  T  hence  2  and P  <<  P  (n-x) i s  PV 2 1 - + RT  PV 2 2 RT  1  f2 31 J  2  C-)  P T 2 1 = =;— 1 ~ 2  (2.5)  :  2  and  P V T 2 2 1 P~V + p v - P V 11 12 • 2 1  T, = •=— l  The c o n d i t i o n s p r e v a i l i n g  =  2  Thus  2  p fV + V ) l 1 2' --— — RT^  and V  2  v  +  2 4  V 1 where v = rr~ 2  V  i n t h e c r y o s t a t when i n use a r e such t h a t v  <  1  so t h a t  T  2  =  4^T)  ] 2 p  ( 2  T  2  = kP  2  where k = -  6 )  l  T  or  '  C -7) 2  p  ( v + 1 )  The sample chamber was f i l l e d w i t h h e l i u m t o about one atmosphere a t room t e m p e r a t u r e and t h e t a p c l o s e d . obtained:  On c o o l i n g , two c a l i b r a t i o n p o i n t s were  one a t l i q u i d n i t r o g e n temperature  h e l i u m temperature  (4.2°K).  (77°K) and t h e o t h e r a t  liquid  Other t e m p e r a t u r e s i n t h e ' r a n g e 4.2°K t o 77°K  were then f o u n d a p p r o x i m a t e l y from t h e measured(P ) by l i n e a r  interpolation.  _ 37 -  E.  Apparatus  A b s o r p t i o n and Prompt Luminescence S t u d i e s All  low-temperature p o l a r i z e d a b s o r p t i o n and e m i s s i o n s p e c t r a were photo-,  graphed w i t h a H i l g e r and Watts E201 l a r g e L i t t r o w S p e c t r o g r a p h o p t i c s on Kodak 103 a-0 and 103 a-F p l a t e s .  with quartz  The e x t e r n a l o p t i c a l system  d i s p l a y e d i n F i g . 4 was c o n s t r u c t e d w i t h f u s e d s i l i c a l e n s e s .  A lens  the l i g h t source on t o t h e sample; then t h e t r a n s m i t t e d o r e m i t t e d was p o l a r i z e d and f o c u s e d on t h e s l i t by a W o l l a s t o n u n i t .  focused  light  The W o l l a s t o n  u n i t c o n s i s t e d o f a p r i s m w i t h two a d j u s t a b l e planoconvex l e n s e s on e i t h e r s i d e t o ensure passage o f p a r a l l e l l i g h t through t h e p r i s m and p r o p e r ing a t the s l i t .  focus-  The two beams were s e p a r a t e d by 4 mm p r o v i d i n g ample space  f o r an i r o n a r c c a l i b r a t i o n between them.  LIGHT SOURCE  LENS  18 cm-  Fig. 4  SAMPLE HOLDER  18cm  WOLLASTON UNIT  32cm-  SLIT  •32cm  E x t e r n a l o p t i c a l system used f o r a b s o r p t i o n and luminescence experiments.  The  c r y s t a l s were a l i g n e d i n t h e o p t i c a l t r a i n u s i n g t h e p r i n c i p l e o f 49  the p o l a r i z i n g m i c r o s c o p e .  With a v i s i b l e - l i g h t s o u r c e and no sample i n  p l a c e , a p i e c e o f p o l a r o i d was p l a c e d b e f o r e t h e sample h o l d e r , and r o t a t e d  - 38 -  to e x t i n g u i s h  one beam from t h e W o l l a s t o n p r i s m as i n d i c a t e d by a  minimum c u r r e n t from a p h o t o m u l t i p l i e r mounted on a Beckman DU monochromator.. Then t h e s i n g l e c r y s t a l sample was  i n s e r t e d i n t o t h e o p t i c a l t r a i n and t h e  complete h o l d e r r o t a t e d u n t i l a new minimum i n the p h o t o c u r r e n t reached.  I n t h i s way  was  t h e sample and W o l l a s t o n e x t i n c t i o n d i r e c t i o n s  were a l i g n e d t o w i t h i n one degree.  The room-temperature  crystal spectra  were measured on t h e m o d i f i e d Beckman DU s p e c t r o m e t e r . " ^ A PEK 75 W Xenon lamp was used as c o n t i n u o u s l i g h t s o u r c e f o r a b s o r p o  t i o n experiments. mercury and 3 mm  F l u o r e s c e n c e e x c i t a t i o n was a c c o m p l i s h e d w i t h t h e 3131  l i n e i s o l a t e d by 5 cm o f p o t a s s i u m chromate s o l u t i o n (0.200 C o r n i n g f i l t e r CS 7-54  Some phosphorescence  from a PEK  100 W mercury (  s p e c t r a were photographed  A  gm/1)  lamp.  with a Jarrell-Ash  3/4  o  meter, f/6.3 g r a t i n g s p e c t r o g r a p h w i t h a d i s p e r s i o n o f 22 A/mm Delayed Luminescence  i n 1st o r d e r .  Studies  D e l a y e d l u m i n e s c e n c e e x c i t a t i o n was p r o v i d e d by t h e l i g h t from a PEK model 401 mercury  lamp o p e r a t e d a t an output o f 100W  f o c u s e d on t o a sample  p l a c e d i n t h e heat exchange chamber o f the m o d i f i e d l i q u i d h e l i u m c r y o s t a t . The prompt f l u o r e s c e n c e was  s e p a r a t e d from t h e d e l a y e d e m i s s i o n by means o f  a s l o t t e d r o t a t i n g can phosphoroscope p o r t i o n of the helium c r y o s t a t .  The  mounted around t h e o u t s i d e o f t h e lower e m i s s i o n was passed t h r o u g h a Spex  model 1700-11 ( C z e r n y - T u r n e r , 3/4 meter, f/6 s p e c t r o m e t e r / s p e c t r o g r a p h ) w i t h o  o  a g r a t i n g b l a z e d a t 7500 A and a d i s p e r s i o n o f 10 A/mm. 250 m i c r o n s .  The e m i s s i o n was d e t e c t e d by an RCA  mounted a t the e x i t s l i t . micro-microammeter,  1P28  The s l i t w i d t h photomultiplier  The p h o t o c u r r e n t was a m p l i f i e d by a K e i t h l y  and d i s p l a y e d on a B r i s t o l c h a r t r e c o r d e r .  o f t h e d e l a y e d f l u o r e s c e n c e and'phosphorescence  was  The  414  intensity  was m o n i t o r e d over a wide  - 39 range o f t e m p e r a t u r e s .  The  -  :  l i f e t i m e s were measured from the decay o f  the  p h o t o m u l t i p l i e r s i g n a l from an i n t e n s e e m i s s i o n peak; a f t e r c u t t i n g o f f the l i g h t s o u r c e , t h e decay was 40  F.  f o l l o w e d on a r e c o r d e r o p e r a t i n g a t a speed o f  in./min.  Infrared Spectra The  i n f r a r e d s p e c t r a were r e c o r d e d  301 and 421).  on P e r k i n - E l m e r  spectrometers  P o l a r i z e d spectra were o b t a i n e d u s i n g P e r k i n - E l m e r  g r i d p o l a r i z e r s on s i l v e r bromide o r polyethylene s u b s t r a t e s .  (models  gold  wire  A number o f  s u i t a b l e s o l v e n t s were a v a i l a b l e f o r the f a r i n f r a r e d r e g i o n , ^ but c y c l o hexane p r o v e d to be most s u i t a b l e f o r o r g a n i c m o l e c u l e s .  A 1 cm c e l l  equipped  w i t h p o l y e t h y l e n e windows and f i l l e d w i t h a s a t u r a t e d s o l u t i o n o f the compound i n c y c l o h e x a n e was  p l a c e d i n the sample beam.  f i l l e d w i t h c y c l o h e x a n e was  u t i l i z e d t o a t t e n u a t e the r e f e r e n c e beam.  G.  A matching  organic  cell  Raman S p e c t r a  o Raman s p e c t r a o f c a r b a z o l e were e x c i t e d by the 4880 A l i n e from an argon i o n gas  l a s e r operated  a t a nominal o u t p u t power o f 50 mW.  The  o 4880 A l i n e was  i s o l a t e d from o t h e r l i n e s i n t h e d i s c h a r g e u s i n g an  inter-  o f e r e n c e f i l t e r w i t h a 10 A band w i d t h . 1P28  The  s p e c t r a were d e t e c t e d by an  RCA  p h o t o m u l t i p l i e r mounted at the e x i t s l i t o f the Spex model 1700-11  spectrometer.  The p h o t o m u l t i p l i e r o u t p u t was  a m p l i f i e d by a K e i t h l y 414 • • i  micro-microammeter and r e c o r d e d by a B r i s t o l r e c o r d e r .  A second method, 1  s l i g h t l y more s e n s i t i v e but l e s s s a t i s f a c t o r y from t h e p o i n t o f view of o p e r a t i n g c o n d i t i o n s was was  a l s o used t o a m p l i f y the s i g n a l . :  The  chopped at about 1 kc and the p h o t o m u l t i p l i e r o u t p u t was  laser light  sent t o a  r e c o r d e r t h r o u g h a narrow band a m p l i f i e r and phase s e n s i t i v e d e t e c t o r .  •  • •  •  Iif  The  - 40 -  l i m i t o f t h e d e t e c t i o n was s e t by t h e o p t i c a l n o i s e a r i s i n g from  ghosts  and s a t e l l i t e s a t t h e l a s e r f r e q u e n c y s c a t t e r e d from t h e g r a t i n g .  The  s p e c t r a l band pass was s e t a t about 5 cm ^ and t h e r e p r o d u c i b i l i t y i n l i n e measurement was u s u a l l y l e s s than t h i s . The c r y s t a l and s o l u t i o n Raman s p e c t r a o f f l u o r e n e and d i b e n z o t h i o p h e n e were e x c i t e d by a helium-neon  gas l a s e r o p e r a t i n g a t 90 mW,  r e c o r d e d u s i n g a Cary 81 s p e c t r o m e t e r .  and were  The s l i t w i d t h corresponded t o a  s p e c t r a l band pass o f 5 cm ^.  H.  Measurement o f S p e c t r a S p e c t r a l band p o s i t i o n s were measured from p h o t o g r a p h i c  enlargements  (Kodabromide 5A p a p e r ) o f t h e s p e c t r o s c o p i c p l a t e s w i t h t h e a i d o f a measuring  box.  The measuring  box c o n s i s t e d o f a h a i r l i n e mounted i n p l e x i -  g l a s s and a t t a c h e d t o an i l l u m i n a t e d box so t h a t i t t r a v e l l e d a t r i g h t a n g l e s t o a p r e c i s e l y engraved  ruler.  was e s t i m a t e d t o be 0.1 mm. positions  The a c c u r a c y i n measurement between l i n e s  A t f i r s t , t h e method used t o c o n v e r t  line  on a p r i n t t o vacuum wavenumbers assumed t h a t t h e d i s p e r s i o n o f  t h e p r i s m s p e c t r o g r a p h was l i n e a r i n wavenumber over s m a l l d i s t a n c e s .  Two  i r o n a r c l i n e s were chosen near t o an unknown l i n e , i d e n t i f i e d i n Angstroms 52 u s i n g i r o n a r c c h a r t s i n Brode, 53 s u i t i n g Kayser's T a b l e s ,  c o n v e r t e d t o vacuum wavenumbers by con-  and f i n a l l y the p o s i t i o n o f t h e unknown  determined by i n t e r p o l a t i o n between t h e two s t a n d a r d l i n e s .  line  The a c c u r a c y  o f t h e method was e s t i m a t e d t o be about 1 cm *. . D u r i n g t h e l a t t e r h a l f o f the work done f o r t h i s t h e s i s , a computer programme was a v a i l a b l e t o e v a l u a t e t h e l i n e p o s i t i o n s .  A c a l i b r a t i o n curve  f o r each s t r i p was o b t a i n e d by a l e a s t squares f i t t o a t h i r d degree polynomi  - 41 -  X = A +.Bx + C x  from a number o f i r o n a r c l i n e s . on t h e number o f i r o n l i n e s .  2  + Dx  3  The a c t u a l degree o f t h e e q u a t i o n depends  Any m i s a s s i g n e d  i r o n l i n e s were d e t e c t e d by  the poor f i t t o t h e d i s p e r s i o n e q u a t i o n and r e j e c t e d by t h e programme. p o s i t i o n s o f t h e s p e c t r a l l i n e s were computed from- t h e c a l i b r a t i o n  The  curve,  c o r r e c t e d t o vacuum wavelength u s i n g E d l i n ' s f o r m u l a , and t h e n c o n v e r t e d t o wavenumbers.  The a c c u r a c y  o f t h e two methods was comparable; t h e l a t t e r  method however e x p e d i t e d t h e t e d i o u s p r o c e d u r e o f measuring l i n e s . Line i n t e n s i t i e s required f o r the v i b r a t i o n a l a n a l y s i s of absorption and  f l u o r e s c e n c e s p e c t r a were e s t i m a t e d  Joyce-Loebl  I,  from t r a c i n g s o f p l a t e s made w i t h a  model MK I I I C d o u b l e beam r e c o r d i n g  microdensitometer.  C r y s t a l d a t a and o p t i c a l p r o p e r t i e s o f some o r g a n i c  Biphenyl Crystal  compounds.  (C H ) 1 2  data^  1 0  4  M o l e c u l a r weight = 154.2; m e l t i n g p o i n t = 71°C. o  5.64, c_ = 9.47 A, 3 = 95.4°. unit c e l l .  M o n o c l i n i c , a. = 8.12, _b =  •  P e r f e c t cleavage  coincident with the molecular 45 Optical properties  Space group 2 / a p  1  '  T w o  ab_ p l a n e ; secondary cleavage  molecule per (201) v e r y n e a r l y  plane.  O p t i c a x i a l p l a n e a_c; acute b i s e c t r i x n e a r l y p a r a l l e l t o t h e long  molecular  a x i s , Z A C = -20.5°. The p l a n a r i t y o f t h e b i p h e n y l m o l e c u l e f o r some t i m e .  has been a s u b j e c t o f d i s c u s s i o n  E l e c t r o n d i f f r a c t i o n s t u d i e s show c o n c l u s i v e l y t h a t t h e f r e e  m o l e c u l e i s n o n - p l a n a r t o t h e e x t e n t t h a t t h e d i h e d r a l a n g l e i s 4 2 ° ^ , and a.recent  c a r e f u l study o f t h e c r y s t a l r e v e a l e d - s l i g h t  deviations-from  - 42 The m o l e c u l a r p o s i t i o n s a r e i l l u s t r a t e d i n F i g . 5 and t h e  planarity.  d i r e c t i o n c o s i n e s r e l a t i n g t h e m o l e c u l a r and c r y s t a l axes a r e l i s t e d i n T a b l e 1. Table 1  D i r e c t i o n cosines of b i p h e n y l X  * a  0.8289  0.5563  -0.0163  a  • 0.7986  0.5177  0.3031  b  0.5465  -0.8376  -0.0066  -0.2522  -0.1744  0.9529  0.0125  -0.0004  0.9996  * c_  Note:  Fluorene  z  Y.  The c and a  a x i s i s t h e [102] d i r e c t i o n i s p e r p e n d i c u l a r t o b and c_ .  (C^H^) 57  C r y s t a l data M o l e c u l a r weight = 166.2; m e l t i n g p o i n t = 116-7°C. b_ = 5,721, £ = 1 8 . 9 7 A. cell.  Space group Pnam (£>2h ' J  O r t h o r h o m b i c , a_ = 8,49, Four m o l e c u l e s P  e r  unit  P e r f e c t c l e a v a g e ab p l a n e . 45  Optical properties O p t i c a x i a l p l a n e ab; a c u t e b i s e c t r i x / / c . The m o l e c u l e p o s s e s s e s a p l a n e o f symmetry which i s p a r a l l e l t o t h e ab c r y s t o l l o g r a p h i c p l a n e and p l a c e s t h e long a x i s o f t h e m o l e c u l e p a r a l l e l t o t h e c_ a x i s o f t h e c r y s t a l .  The d i s p o s i t i o n o f t h e m o l e c u l e s i n t h e u n i t  c e l l i s shown i n F i g , 6 and t h e d i r e c t i o n c o s i n e s a r e t a b u l a t e d i n T a b l e 2.  -•••-45 ~  Fig.  5 Biphenyl u n i t  cell  y  1  2  /  iC  V  /"ID  a  Fig.' 6. F l u o r e n e u n i t  cell  _ 44 -  Table 2  D i r e c t i o n cosines of fluorene X  Y.  z  a_  0.821  0  0.571  b  0.571  0  -0.821  c_  0  1  0  C a r b a z o l e (C,„H N) C r y s t a l data M o l e c u l a r weight = 167.2; m e l t i n g p o i n t = 247°C. ° b_ = 19.15, c_ = 5.74 A. cell.  16  Space group Pnam  •  Orthorhombic, F°  u r  a =7.76,'  molecules per u n i t  P e r f e c t c l e a v a g e p l a n e a c , ^ p l a t e - l i k e c r y s t a l s from e t h a n o l w i t h 59  w e l l d e v e l o p e d ax f a c e . Optical properties O p t i c a x i a l p l a n e ab_; a c u t e b i s e c t r i x //b_. The m o l e c u l e i s s l i g h t l y n o n - p l a n a r i n t h e c r y s t a l b e i n g bent about t h e 59 z_ a x i s t o t h e e x t e n t t h a t t h e a n g l e between t h e two benzene r i n g s i s 178.4. S i n c e t h e d i s t o r t i o n from p l a n a r i t y i s s m a l l i t w i l l be a s u f f i c i e n t l y a p p r o x i m a t i o n t o t r e a t t h e m o l e c u l e as though i t r e t a i n s f u l l  covering  symmetry. The o r i e n t a t i o n o f t h e m o l e c u l a r a x i e s w i t h r e s p e c t t o t h e c r y s t a l axes i s i l l u s t r a t e d i n F i g . 8 and s p e c i f i e d by t h e d i r e c t i o n c o s i n e s i n 59 T a b l e 3. The m o l e c u l a r d i m e n s i o n s a r e shown i n F i g . 7. Table 3 D i r e c t i o n c o s i n e s o f c a r b a z o l e  a  0.8771  b  0  c  0.4803  0  0,4803 1  0  0 0.8771  close  - .45 ^  Fig. 8  Carbazole u n i t  cell  Fig.  9  Dibenzothiophene u n i t  cell  D i b e n z o t h i o p h e n e ( C . i S) -• 1/ o Crystal  data^  M o l e c u l a r weight = 183.4; m e l t i n g p o i n t = 99°C. O  b = 5.998, c = 18.705 A,  M o n o c l i n i c , §_ = 8.667,  ,  r  3  = 113.91°.  Space group ?  2  ^  (C^) .  Four  m o l e c u l e s per u n i t c e l l . Optical properties O p t i c a x i a l p l a n e ac_; e i t h e r the a c u t e or obtuse b i s e c t r i x was  (the exact  not d e t e r m i n e d ) c o i n c i d e s w i t h t h e b i s e c t o r o f the a n g l e Fig.  choice  3 .  9 d i s p l a y s the p o s i t i o n of the molecules i n the u n i t c e l l ,  the r e l a t i o n s h i p o f the m o l e c u l a r  axes t o t h e c r y s t a l a x e s .  by the o r t h o g o n a l  s_, i s o u t l i n e d w i t h a d o t t e d l i n e i n F i g . 9;  edges r_, b, and  The  cell  and defined  - 47 r bisects  3  samples.^  and r b l o c a t e s t h e p r i n c i p l e c l e a v a g e p l a n e o f t h e melt-grown The o r i e n t a t i o n o f t h e m o l e c u l a r axes w i t h r e s p e c t t o t h e a, 1)  and r , b, s axes a r e g i v e n by t h e d i r e c t i o n c o s i n e s i n T a b l e s 4 and 5. mean m o l e c u l a r parameters  Th  a r e shown i n F i g . 10 f o r a p l a n a r m o l e c u l e  a l t h o u g h t h e m o l e c u l e i s s l i g h t l y bent about t h e z a x i s so t h a t t h e a n g l e between t h e benzene r i n g s i s 178.7°.  Table 4  D i r e c t i o n cosines of dibenzothiophene z  X  a_  0.7534  0.5133  -0.4085  b  0.4712  0.0092  0.8820  0.4587  0.8581  0.2350  Table 5  D i r e c t i o n c o s i n e s o f dibenzothiophene X  F i g . 10  X  z.  r.  -0.1235  0.9912  0.0704  b_  0.4715  0.0092  -0.8819  J2.  0.8732  0.1324  0.4685  Bond l e n g t h s and bond a n g l e s o f d i b e n z o t h i o p h e n e  Chapter 3 A  V i b r a t i o n a l Assignment o f C a r b a z o l e from  Infrared,  Raman, and F l u o r e s c e n c e S p e c t r a  A.  Introduction A number o f f a i r l y complete v i b r a t i o n a l assignments have been made 62 71  f o r a r o m a t i c hydrocarbons w i t h a t l e a s t t h r e e r i n g s such as a n t h r a c e n e , 41,72-76 , . 77 78 79 phenanthrene , p h e n a z m e , pyrene , and p e r y l e n e . These assignments have been based l a r g e l y on the r a t h e r complex i n f r a r e d of  s i n g l e c r y s t a l samples.  spectra  I n most c a s e s , t h e a n a l y s i s of t h e s e s p e c t r a  r e l i e s on t h e assumptions t h a t t h e s t r o n g e r l i n e s mark the p r e s e n c e o f fundamentals and t h a t d e p a r t u r e s from the o r i e n t e d - g a s p r e d i c t i o n s a r e not s e v e r e as t o r e v e r s e p o l a r i z a t i o n r a t i o s .  The u s u a l outcome i s t h a t the  s e l e c t i o n o f t h e l a s t few fundamentals i n each symmetry b l o c k n e c e s s a r i l y i n v o l v e s a r a t h e r a r b i t r a r y c h o i c e between many l i n e s o f moderate s t r e n g t h t h a t i n d i c a t e the p r e s e n c e o f e i t h e r weak fundamentals or c o m b i n a t i o n s . 73 74 One method t h a t has been used  '  t o r e s o l v e t h i s dilemma i s t o c a l -  c u l a t e a p p r o x i m a t e v a l u e s f o r t h e fundamentals u s i n g s i m p l i f i e d  force  f i e l d s which have been e x t r a p o l a t e d from t h o s e o f s m a l l e r m o l e c u l e s .  The  few fundamentals m i s s i n g from t h e e x p e r i m e n t a l assignment a r e l o c a t e d from these roughly c a l c u l a t e d frequencies. f i n a l c a l c u l a t i o n s may  There i s a r e a l danger here t h a t the  c a r r y the r e s u l t o f an i n i t i a l m i s a s s i g n m e n t .  r e c e n t c a l c u l a t i o n * ^ has attempted t o a p p l y a u n i f i e d v a l e n c e f o r c e  A field  s i m u l t a n e o u s l y t o benzene, n a p h t h a l e n e , a n t h r a c e n e and some d e u t e r a t e d  -  49 -  d e r i v a t i v e s ; i n t h i s case t h e e f f e c t s o f any i n a d v e r t e n t m i s a s s i g n m e n t s are p r o b a b l y  minimal,  An a l t e r n a t i v e p r o c e d u r e was a p p l i e d t o c a r b a z o l e .  For molecules  l a c k i n g an i n v e r s i o n c e n t e r , t h e d a t a d e r i v e d from t h e i n f r a r e d s p e c t r a may be u s e f u l l y supplemented from f l u o r e s c e n c e and Raman s t u d i e s .  Because  o f t h e d i f f e r e n t forms t h a t t h e t r a n s i t i o n moment i n t e g r a l s take t h e r e i s a chance t h a t fundamentals t h a t a r e weak i n an i n f r a r e d spectrum may be r e l a t i v e l y s t r o n g i n f l u o r e s c e n c e o r Raman s p e c t r a . complete an assignment o f t h e m o l e c u l a r p o s s i b l e was made from e x p e r i m e n t a l  I n t h i s c h a p t e r , as  fundamentals o f c a r b a z o l e as  r e s u l t s , and t h e d a t a was used t o t e s t  the f o r c e f i e l d s t h a t have been employed s u c c e s s f u l l y on o t h e r m o l e c u l e s by 64,65,73  r  Califano  B.  S e l e c t i o n Rules 80 The  carbazole molecular  axes x, v_, and z_ ( F i g . 8) have been chosen  such t h a t z_ i s t h e i n - p l a n e a x i s p a s s i n g t h r o u g h t h e n i t r o g e n atom and transforms  l i k e A^ w h i l e x i s t h e m o l e c u l a r  i b l e representation of the out, although  molecular  p o i n t group.  retaining f u l l  c o v e r i n g symmetry.  may i n d u c e t h e i n f r a r e d f o r b i d d e n  The  t o t r e a t t h e m o l e c u l e as  However, t h i s m o l e c u l a r bands ( i n C^)  distortion  t o appear weakly a l o n g  axes.  s e l e c t i o n r u l e s f o r t h e f r e e m o l e c u l e and c r y s t a l may be deduced  from T a b l e 6. one  As p r e v i o u s l y p o i n t e d 59  the carbazole molecule i s s l i g h t l y non-planar i n t h e c r y s t a l  i t - w i l l be a s u f f i c i e n t l y c l o s e a p p r o x i m a t i o n  the b c r y s t a l  normal spanning t h e B^ i r r e d u c -  Of t h e twenty one A^ f u n d a m e n t a l s , t h e r e a r e f o u r C-H and  N-H s t r e t c h i n g modes so t h a t s i x t e e n a r e expected below  There a r e a l s o f o u r C-H s t r e t c h e s o f B  symmetry.  2000  cm *.  Each f r e e m o l e c u l e s t a t e  ,  - 50 -  g i v e s r i s e t o f o u r c r y s t a l s t a t e s , each w i t h t h e v a l u e f o r t h e k_ v e c t o r equal t o zero. c r y s t a l states  Two o f t h e s e c r y s t a l s t a t e s a r e Raman a c t i v e . a r e i n f r a r e d a c t i v e i n t h e case o f A^ o r  The r e m a i n i n g  free molecule  v i b r a t i o n s , a l t h o u g h o n l y one may appear i n t h e i n f r a r e d spectrum ( p a r a l l e l t o t h e b_ c r y s t a l a x i s ) f o r B^ v i b r a t i o n s .  A^ f r e e m o l e c u l e modes may g i v e  r i s e t o v e r y weak b p o l a r i z e d bands i n t h e i n f r a r e d spectrum s i n c e molecular interactions molecule. the  i n t h e c r y s t a l mix A^ and  states  inter-  of the i s o l a t e d  The numbers o f l a t t i c e f r e q u e n c i e s and t h e i r d i s p o s i t i o n amongst  i r r e d u c i b l e r e p r e s e n t a t i o n s o f t h e f a c t o r group a r e a l s o shown i n T a b l e 6.  T a b l e 6.  Correlation  t a b l e showing t h e s e l e c t i o n r u l e s f o r t h e i s o l a t e d 3.  m o l e c u l e and f o r t h e c r y s t a l . S i t e group  M o l e c u l a r group C  N  F a c t o r group  C  2v  D  s  2h  Bases  Bases  A 21 10  xx,yy,zz;z  g 2g  i  A  xz;x  B  B  9 20  xy_ yz;y  ^ 2 B  A"  1  lu ?3u  3g A u B  2u  n  aa,bb,cc  3  ac  3  c  2  a  2  ab  3  .be  3 3  b  2  N i s t h e number o f fundamentals i n t h e f r e e m o l e c u l e and n i s t h e number o f l a t t i c e f r e q u e n c i e s w i t h k = 0.  100 Fig.  11  200  i  r  300  400  500  • 600  cm"  Low f r e q u e n c y i n f r a r e d s p e c t r a o f c a r b a z o l e . (a) ac_ s e c t i o n ; c r y s t a l t h i c k n e s s .19 mm below 160 c m and .053 mm above 160 c m ( f o r t h e r e g i o n 160-250 c m low t r a n s m i s s i o n i s from a sample 1 mm t h i c k ) ; f u l l l i n e / / a , b r o k e n l i n e / / c . (b) be s e c t i o n ; c r y s t a l t h i c k n e s s 1 mm below 160 c m and .15 mm above 160 c m ~ l ; f u l l l i n e //b_, b r o k e n l i n e / / c . -1  -1  -1  -1  (b) 70 p t h i c k b_c s e c t i o n ;  full  l i n e //b_,  broken l i n e  //c_.  - 53 C.  The  Infrared  Spectrum  The p o l a r i z e d i n f r a r e d s p e c t r a were r e c o r d e d w i t h l i g h t i n c i d e n t on ac_ and bc_ f a c e s and a r e shown as F i g s . 11 and 12.  T a b l e 7 l i s t s the observed  f r e q u e n c i e s o f t h e bands and t h e i r assignments made on t h e assumption d e v i a t i o n s from an o r i e n t e d gas model are s m a l l .  that  In t h i s a p p r o x i m a t i o n the  r e l a t i v e i n f r a r e d band i n t e n s i t i e s a l o n g the c r y s t a l axes  (see T a b l e 8) are  g i v e n as t h e square o f t h e d i r e c t i o n c o s i n e s o f t h e m o l e c u l a r axes on t h e c r y s t* a li axes. 59  Table 7  //a_-  The i n f r a r e d spectrum o f c a r b a z o l e  //b_  //c 49  Symmetry  vw  lu  69 m 103  3u  vw 104  mw  127 s  2u lu bg +comp. B^ u  129  vw  b  o  2u  148 m 218  221 s  ms  A,  310 w 379 sh 418  mw  451 s  438 v s 505 m 548 w 570  562 m  ms 576  vw 603 sh  616 658 m  mw 658 m  A  f  - 54 -  //a  //b  //£  Symmetry  723 s  B  l  733 sh  B  2  737 ms  B  2  720 v s  742 v s  740 m  B  l  750 sh  751 v s  A  l  756 m  B  2  772 m  B  2  835 s  B  2  A  l  B  2  B  l  B  2  B  2  852 s  851 ms 859 w  873 sh  873 sh . 878 m 909 vw 910 s  910 s  924 v s  928 s  B  l  966 mw  A  l  979 w  B  2  995 s  B  2  1006 ms  1010 m  2  1062 w  B  2  1070 w  A  l  1109 ms  A  l  B  2  A  l  B  2  B  l  1158 ms  B  2  1173 ms  B  2  1204 ms  B  2  1136 s 1146 sh 1152 w  1223 m  l  B  1123 sh  /'  A  1022 ms  1102 vw  1203 ms  l  A  . 1200 s 1223 m  l A A  1 ?  - 55 -  //a  //b  //c  symmetry  1233 s 1270 m  V  1286 vw  1284 s  1305 mw  1307 m 1320 s  1332 ms  1327 s  1349 sh  1346? 1357 mw 1380 v s 1422 ms  1418 sh  1418 sh  1444 ms  1442 s  B ? 1 A,  1452 v s 1478 vw  1480 m 1490 s 1509 vw  A,  1537 vw 1540 mw 1560 mw 1575 w 1577 sh  1577 w  A,  1594 vw 1609 sh  1610 sh  1620 ms  1620 s 1643 sh 1667 mw 1694 s 1739 m 1749 m  1788 m  1788 m B,  1819 m 1868 m 1899 m  1899 m  - 56 -  //a  //b  //£  symmetry  1912 mw 1916 w  B  1916 mw  2 l  A  1940 mw  B  2  2467 mw  B  2  2597 w  2597 mw  l  A  2663 w  B  2  2728 mw  B  2  2774 w  B  2  2825 mw  B  2  2940 m  B  2  2973 mw  3039 ms  3017 sh  3017 sh  l  A  B  l  3030 m  B  2  3050 v s  B  2  3027 m  3055 s  A  l  3075 mw  3077 ms  A  l  3082 sh  3084 m  A  l  3094 m  B  2  3150 mw  B  2  3410 v s  T a b l e 8,  3421 v v s  A  l  R e l a t i v e i n f r a r e d band i n t e n s i t i e s o f c a r b a z o l e a l o n g t h e c r y s t a l axes c a l c u l a t e d f o r t h e o r i e n t e d gas model.  a  0.231  0.769  0.000  b  0.000  0.000  1.000  c  0.769  0.231  0.000  - 57 L a t t i c e modes, r e f e r r e d t o h e r e and i n T a b l e s 7 and 9 u s i n g lower case symbols, a r e expected a t low f r e q u e n c i e s as l i n e s p o l a r i z e d a l o n g o n l y one crystal axis. assigned  Thus t h e two £ p o l a r i z e d l i n e s a t 49 and 104 cm * a r e  as b ^ , t h e two b_ p o l a r i z e d l i n e s a t 103 and 129 cm * as b^ and u  u  the two £ p o l a r i z e d l i n e s a t 69 and 127 cm'' as b ^ l a t t i c e modes. 1  The  l i n e a t 127 cm * was s t r o n g and q u i t e broad and was thought t o be made up o f two c o n t r i b u t i o n s : one d e r i v e d from t h e b_ l a t t i c e mode mentioned above 3u and a n o t h e r (weaker) c o n t r i b u t i o n marking the p r e s e n c e o f t h e B^ component o f a carbazole  f r e e molecule fundamental.  u  crystal  The spectrum o f a s o l u t i o n o f  i n p y r i d i n e was measured i n t h e low energy r e g i o n and t h e lowest  f r e q u e n c y l i n e was observed weakly a t 140 cm * i n a c e l l o f l e n g t h 1 mm. The weakness o f t h e spectrum was due t o t h e low c o n c e n t r a t i o n a v a i l a b l e and t h e c e l l  l e n g t h was l i m i t e d by t h e s m a l l amount o f l i g h t  b y the solvent.  transmitted  I f t h e s o l v e n t s h i f t i s about t h e same i n s o l u t i o n as i n  t h e c r y s t a l t h e n t h e s o l u t i o n l i n e a t 140 cm * s h o u l d be t h e mean o f t h e f r e q u e n c i e s o f t h e f o u r c r y s t a l components, o n l y two o f which a r e observed -1 -1 a t 148 cm The  and a t about 127 cm  assignments o f t h e l i n e s a t 658, 1223 and 1418 cm * a r e u n c e r t a i n  s i n c e t h e components i n a_ and _c p o l a r i z a t i o n a r e o f v e r y n e a r l y intensity.  equal  I t may be t h a t t h e s e l i n e s a r e complex i n t h a t they c o n t a i n  c o m b i n a t i o n s o f f r e e m o l e c u l e symmetry o p p o s i t e t o t h a t o f t h e main c o n t r i b u t i o n o r t h a t c r y s t a l induced m i x i n g w i t h t h e s t r o n g l i n e s a t 723, 1200, and  1442 cm ^ r e s p e c t i v e l y d i s t u r b s t h e p o l a r i z a t i o n r a t i o .  I f the l a t t e r  i n t e r p r e t a t i o n i s c o r r e c t t h e l i n e a t 1223 cm * should be r e a s s i g n e d as with s u f f i c i e n t  i n t e n s i t y mixed-in t o reverse the p o l a r i z a t i o n r a t i o .  Only t h e more prominent l i n e s above 2000 cm ^ a r e i n c l u d e d i n ' T a b l e 7.  - 58 -  The  i n t e r p r e t a t i o n s u g g e s t e d i n t h e T a b l e , t h a t t h e s t r o n g C-H  fundamentals o f A^ symmetry have s u f f e r e d need n o t be c o r r e c t .  a l a r g e f a c t o r group  The a l t e r n a t i v e i s t o suppose t h a t  stretching splitting  combinations o f  moderate i n t e n s i t y e x i s t a t t h e s e e n e r g i e s ; c e r t a i n l y t h e even s t r o n g e r N-H s t r e t c h a t 3420 cm ^ does n o t show so l a r g e a s p l i t t i n g .  D.  The Raman S p e c t r a I f g and a'  are p o l a r i z a b i l i t y tensors defined  with respect to the  p r i n c i p a l axes x,%_,z_ o f t h e m o l e c u l e and a_,b_,c^ o f t h e c r y s t a l r e s p e c t i v e l y , t h e n i n the o r i e n t e d  gas model  ct' = U  a U  (3.1)  where U d e f i n e s t h e t r a n s f o r m a t i o n from t h e m o l e c u l a r t o t h e c r y s t a l frames.  I n t h i s a p p r o x i m a t i o n t h e i n t e n s i t i e s ( I ) o f t h e Raman s c a t t e r i n g  of t h e c r y s t a l a r e r e l a t e d t o those o f t h e i s o l a t e d m o l e c u l e by t h e equations  aa  592  _ ac_  .710  1.000  bb cc  .053  "i XX  I  053  .592  177  .177  .710 .290  i  ab_ yy zz  and  fbc.  ".769  -  .231  .23l" .769  J  I xy. I Ly_zj  I L xzJ (3.2)  The  Raman l i n e s o b s e r v e d i n a l l p o s s i b l e  c o l l e c t e d i n T a b l e 9 and t h e s p e c t r a spectra  crystal orientations are  a r e shown i n F i g s . 13 and 14. The  i n F i g . 14 have been a d j u s t e d t o make t h e most prominent l i n e i n  .- 59 -  each o f t h e s p e c t r a o f e q u a l s t r e n g t h and so t h e r e l a t i v e s t r e n g t h s o f l i n e s f o r d i f f e r e n t o r i e n t a t i o n s o f t h e sample should not be c l o s e l y compared. However i n F i g . 13 -the t h r e e d i f f e r e n t s p e c t r a have not been a d j u s t e d and were r e c o r d e d under as n e a r l y t h e same c o n d i t i o n s as p o s s i b l e .  (ac)  (be)  1  j_  n  O  -200  F i g . 13  (ab)  200  Some low f r e q u e n c y  O  o  200  Raman i n t e r v a l s o f c a r b a z o l e .  200  The nomenclature  i s d e f i n e d i n T a b l e 9.  T a b l e 9.  b(aa)c  The Raman spectrum o f c a r b a z o l e ,  a(bb)c  a(cc)b  a(ca)b  b(ab)c  b(cb)a 28 34  52  3g 3g lg a ?  52? 78 78?  103 104  symmetry  lg a ? g  - 60 -  b(aa)c  a(bb)c  a(cc)b  a(ca)b  b(ab)c  b(cb)a  symmetry  107 108 220  220  108  a  221  A  299  A  305 431  430  569  743  2  V •  432 569  g l  l  A  569  V  658  658  A  l  742  743  A  l  860  860  889  889  V  1015  1017  1014  A  l  1107  1105  1108  A  l  1208  1212  A  l  A  l  1226 1291  1291  1292  A  l  1314  1314  1314  A  l  1339  1338  1340  A  l  1455  1455  1455  A  l  A  l  A  l  A  l  1483 1576  1575  . 1577  1629 3061  3060  3062  A  l  3421  3420  3422  A  l  The column headings i n d i c a t e from l e f t t o r i g h t i n s i d e t h e p a r e n t h e s i s t h e p o l a r i z a t i o n o f t h e i n c i d e n t and s c a t t e r e d l i g h t and from l e f t t o r i g h t outside the parenthesis the propagation d i r e c t i o n s o f the i n c i d e n t and s c a t t e r e d l i g h t .  The l i n e s r e p r e s e n t i n g l a t t i c e modes a r e e s p e c i a l l y s t r o n g and were r e c o r d e d a t reduced s e n s i t i v i t y . the e x c i t i n g  The v e r y weak l i n e s 52 and 78 cm ^ from  l i n e i n t h e (aa) spectrum a r e p r o b a b l y components o f t h e much  (aa)  JL  1—  1  '  i  '  r  A  , A,  /Z. -i  r-  (bb) i  A. ft /  (cc)  I  -200  UA  —r  O F i g . 14  1 200  400  600  .1 800  Raman s p e c t r a o f c a r b a z o l e .  IOOO  ' 1200  ' I4CO  " 1600  7  ^OOO  The n o m e n c l a t u r e i s d e f i n e d i n T a b l e 9.  1  32CO ' 3 4 0 0  - 62  stronger  l i n e s i n the  However the 107  cm  1  -  (ab) spectrum a r i s i n g from i m p e r f e c t  c r y s t a l alignment.  i n t e r v a l i n the. (ac) spectrum i s o f a medium s t r e n g t h  w h i c h c o u l d not be f u r t h e r reduced by s m a l l a n g u l a r a d j u s t m e n t s o f c r y s t a l or the a n a l y s i n g p o l a r o i d and so i s p r o b a b l y v e r y s t r o n g l i n e s i n the (ab) and  103 cm  1  (aa) o r  (be) a r e two  m e n t a l (taken t o be  (cc) s p e c t r a .  the  not a component of  the  P o s s i b l y , the l i n e s at 104  f a c t o r group components o f a m o l e c u l a r  cm  funda-  from energy c o n s i d e r a t i o n s ) .  Because o f low v o l a t i l i t y  (the m e l t i n g p o i n t o f c a r b a z o l e  sample, always f r e s h l y p o l i s h e d w i t h acetone b e f o r e  i s 247°C) the  each s e r i e s o f  were measured, h e l d a f i n e s u r f a c e f i n i s h f o r s e v e r a l d a y s .  spectra  Even so,  s c a t t e r i n g o f t h e e x c i t i n g l i g h t w i t h i n the s i n g l e monochromator was  the so  s e v e r e t h a t o n l y two q u i t e weak n o n - t o t a l l y symmetric fundamentals were recorded.  I t i s p o s s i b l e t h a t the 305  cm  i n t e r v a l i n the  1  i s the Ag f a c t o r group component o f a B^ m o l e c u l a r B_  f a c t o r group component was  and c o n s e q u e n t l y was  1014,  v i b r a t i o n although  not r e p r o d u c i b l y measured i n the  not i n c l u d e d i n T a b l e  I n t e r v a l s o f 744,  (cc) spectrum  1216,  1286,  the  (cc) spectrum  9.  1313,  1356,  1487,  1572  and  1630  cm"  1  81 have been r e p o r t e d  i n the Raman spectrum o f a s o l u t i o n o f c a r b a z o l e  present  in  acetone.  The  s t u d y has not o n l y shown t h a t a l l t h e s e i n t e r v a l s  represent  t o t a l l y symmetric v i b r a t i o n s and found more l i n e s but a l s o a l l o w s  an e s t i m a t e t o be made o f the r e l a t i v e e f f e c t i v e n e s s of each of the t r a n s i t i o n moment o p e r a t o r s . through the operator a E,  The  Fluorescence  The estimated  fluorescence  molecular  For example, v i b r a t i o n s t h a t appear e x c l u s i v e l y  are seen a t 220,  1226,  1483  and  1629  cm  Spectrum spectrum o f c a r b a z o l e  t o be about 15°K  i n f l u o r e n e at a temperature  i s r e p r o d u c e d i n F i g . 15 and an a n a l y s i s o f t h e  27,000 F i g . 15  27,500  28,000  28,500  29,000  29,500  The f l u o r e s c e n c e spectrum o f c a r b a z o l e i n a s i n g l e c r y s t a l m a t r i x o f f l u o r e n e a t about 15 .\.  cm"  - 64 spectrum i s shown i n T a b l e 10. completely reabsorbed.  I n F i g . 15 t h e e l e c t r o n i c o r i g i n i s a l m o s t  From t h e a b s o r p t i o n spectrum (see next c h a p t e r ) i t  i s known t h a t t h e o r i g i n i s s t r o n g l y b p o l a r i z e d so t h a t t h e e l e c t r o n i c t r a n s i t i o n under i n v e s t i g a t i o n may be a s s i g n e d f l u o r e s c e n c e spectrum o f c a r b a z o l e i n b i p h e n y l  — > • '''A^ .  A study o f t h e  (Appendix I ) c o n f i r m e d t h e  assignment o f t h e e l e c t r o n i c o r i g i n , b u t d i d not y i e l d any a d d i t i o n a l i n f o r m a t i o n about t h e v i b r a t i o n a l a n a l y s i s .  However each v i b r o n i c band i n t h e  b i p h e n y l m a t r i x e x h i b i t e d m u l t i p l e t s t r u c t u r e c o n s i s t i n g o f two l i n e s s e p a r a t e d by 22 cm  on t h e average.  1  The f l u o r e s c e n c e spectrum o f phenanthrene  i n b i p h e n y l a l s o shows a d o u b l e t s p l i t t i n g which was a t t r i b u t e d t o e n e r g e t i cally  inequivalent  trapping  s i t e s a r i s i n g from g u e s t - h o s t i n t e r a c t i o n s m a i n l y  82 of a r e p u l s i v e  T a b l e 10.  //b  nature.  The f l u o r e s c e n c e spectrum o f c a r b a z o l e i n f l u o r e n e  //c_  Int  691  Remarks o r i g i n , reabsorbed  30  m  30,  lattice  48  m  48,  lattice  81  m  81,  lattice  108  mw  108,  138  w  30 + 108?  219  vs  219,  250  m  219  427  m  427,  435  ms  2 x 219 - 3  475  w  2 x 219 + 30 + 7  549  ms  549,  B  2  616  m  616,  B  2  vs  654,  k  654  a t about 15°K.  lattice  A  x  +30+1 A  x  - 65 -  //b  //c_  Int  Remarks  687  m  654 + 30 + 3  743  mw  743, A  771  w  219 + 549 + 3  830  w  219 + 616 - 5  874  s  219 + 654 + 1  888  ms  888, A  963  vw  219 + 743 + 1  w  996, I  1000  s  1009,  1040  w  1009  1098  w  2 x 219 + 654 + 6  m  1118,  R  2  1151  mw  1151,  A  l  1204  mw  1204,  A  l  s  1210,  B  mw  2 219 + 1009 + 3  m  1237,  B  1287  vs  1287,  A  1310  vs  l 2 x 654 + 2  1336  vs  1336,  A  1391  s  1391,  B  1427  w  2 219 + 1210 - 2  mw  1453, A j ? ; 2 x 219  m  1461,  B  2  mw  1482,  A  l  m  1487,  996  1118  1210 1231 1237  1453 1461 1482 1487  5  2  l +30-1 A  2  l  1505  m  2 219 + 1287 - 1  1528  m  219 + 2 x 654 + 1  1555  w  219 + 1336  1577  vw  1577,  s  1607,  s  1625,  1607 1625  B  l  A  B  A  2 l  66-  //b  //£  Int  1665  Remarks  ms  654 + 1009 + 2  1680  w  219 + 1461  1709  w  219 + 1487 + 3  1751  vw  743 + 1009 - 1  1802  vw  654 + 1151 - 3  w  549 + 1287  1841  w  219 + 1625 - 3  1886  w  219 + 654 + 1009 + 4  vw  616 + 1287 - 3  1941  m  654 + 1287  1965  <m  3 x 654 + 3  1989  m  2021  w  2 x 1009 + 3  2044  w  2 x 219 + 1607; 654 + 1391 - 1  2112  w  65.4 + 1461 - 3  w  1009 + 1151  mw  654 + 1607 + 2  2278  mw  654 + 1625 - 1  2295  mw  1009 + 1287 - 1  2321  mw  2 x 654 + 1009 + 4  2345  w  1009 + 1336  w  1118 + 1287 - 2  2495  w  1204 + 1287 + 4  2513  w  2 x 654 + 1204 + 1  w  2 x 654 + 1210 + 3  2568  w  2 x 1287 - 6  2593  w  2 x 654 + 1287 - 2  2618  m  4 x 654 + 2; 1287 + 1336 - 7  2641  . m  2671  w  2 x 1336 - 1  2699  w  2 x 654 + 1391 - 4  2723  w  1336. + 1391 - 4  1836  •  1900  2160 2263  2403  2521 ^  °  654 + 1336 - 1  2 x 654 + 1336 - 3  - 67 -  //£  //b  Int  Remarks  2816  vw  219 + 2 x 654 + 1287 + 2  2833  vw  219 + 4 x 654 - 2  2859  w  1210 + 1625 + 4  2894  mw  1287 + 1607 - 3  w  1287 + 1625 - 3  mw  2 x 654 + 1607 --3  2932  w  2 x 654 + 1625 -1  2957  w  1336 + 1625 - 4  3081  vw  3081, A ?  3128  vw  219 + 1287 + 1625 - 3  3149  vw  219 + 2 x 654 + 1625 - 3  3172  vw  219 + 1336 + 1625 - 8  w  1607 + 1625 - 4  3251  w  2 x 1625 + 1  3274  w  5 x 654  3442  w  3442, A j ?  3562  vw  654 + 1287 + 1625 - 4  3608  W W  654 + 1336 + 1625 - 7  2909 2912  3228  The p o s i t i o n o f t h e o r i g i n i s g i v e n i n cm d i f f e r e n c e s from t h e o r i g i n .  The r e g i o n i m m e d i a t e l y  and a l l o t h e r e n t r i e s show  to the r e d o f the fluorescence o r i g i n of carbazole  i n f l u o r e n e was f a i r l y d i f f u s e presumably because o f t h e w e a l t h o f l i n e s t h a t c o u l d n o t be r e s o l v e d .  Since there i s a r e l a x a t i o n of s e l e c t i o n r u l e s  a t t h e s i t e o c c u p i e d by t h e c a r b a z o l e m o l e c u l e  t h e r e i s no s u g g e s t i o n t h a t  the r a t h e r b r o a d maxima a t 30, 48, 81, 108 and 138 cm a  .g  1  n e c e s s a r i l y represent  l a t t i c e modes o f f l u o r e n e . The f l u o r e s c e n c e spectrum i s n o t so w e l l p o l a r i z e d as t h e a b s o r p t i o n  - 68 83 84 spectrum ( v i d e i n f r a ) an e f f e c t * which a l t h o u g h noted b e f o r e understood.  '  , i s not w e l l  However an i m p o r t a n t o b s e r v a t i o n i s t h a t w h i l e b_ p o l a r i z e d  l i n e s have a s t r o n g  p o l a r i z e d component, c_ p o l a r i z e d l i n e s have o n l y a  weak b_ p o l a r i z e d component.  I n t h i s way i t was deduced t h a t t h e l i n e 1210 cm  t o t h e r e d o f t h e o r i g i n marked a  fundamental o f t h e c a r b a z o l e m o l e c u l e  d e r i v i n g i t s i n t e n s i t y by v i b r a t i o n a l i n t e r a c t i o n w i t h a h i g h e r energy e l e c t r o n i c s t a t e and f u r t h e r t h a t t h e 1204 cm fundamental  i n t e r v a l r e p r e s e n t e d an  1  (see T a b l e 1 0 ) .  The t h r e e l i n e s a t 1287, 1310 and 1336 cm  1  appeared i n t h e i n f r a r e d ,  t h e Raman and t h e f l u o r e s c e n c e s p e c t r a b u t w i t h r a t h e r d i f f e r e n t p a t t e r n s i n each c a s e .  intensity  S i n c e i t i s u n l i k e l y t h a t t h e r e s h o u l d be t h r e e A^  fundamentals so c l o s e i n energy one o f t h e t h r e e may r e p r e s e n t a c o m b i n a t i o n a p p e a r i n g i n a l l s p e c t r a t h r o u g h a Fermi resonance w i t h t h e o t h e r two. Assuming t h a t any m i x i n g i s n o t so s e v e r e as t o r e v e r s e i n t e n s i t i e s , t h e p r e s e n c e o f a fundamental a t 1292 cm and a t 1285 and 1330 cm at 1306 cm  1  1  1  i s i n d i c a t e d i n t h e Raman spectrum  i n t h e i n f r a r e d spectrum w h i l e t h e i n f r a r e d  line  i s r e l a t i v e l y weak and p r o b a b l y marks t h e c o m b i n a t i o n sought.  This i n t e r p r e t a t i o n i s not incompatible w i t h the a n a l y s i s given the f l u o r escence spectrum (see T a b l e 10) i n which t h e l i n e a t 1310 cm  1  i s assumed  t o g a i n i n t e n s i t y i n a second way, v i z . t h r o u g h an a p p l i c a t i o n o f t h e Franck-Condon p r i n c i p l e .  T h e r e f o r e , i t may be c o n c l u d e d t h a t t h e r e i s an  A^ c o m b i n a t i o n a t about 1310 cm  1  (not n e c e s s a r i l y t h e o v e r t o n e o f t h e 654 cm  fundamental) which mixes p r i n c i p a l l y w i t h t h e fundamental a t about 1290 cm and p o s s i b l y a l s o (weakly) . w i t h t h e fundamental at. 1336 cm . 1  1  The r e l a t i v e  i n t e n s i t i e s w i t h i n t h e group o f t h r e e l i n e s a r e d e t e r m i n e d i n t h e i n f r a r e d and Raman s p e c t r a by t h e c o e f f i c i e n t s o f m i x i n g , w h i l e i n t h e f l u o r e s cence spectrum some e x t r a i n t e n s i t y must come from t h e Franck-Condon mechanism  - 69 s i n c e i n t h i s case the l i n e at 1310  cm * i s the s t r o n g e s t  of the  three  (see F i g . 15). The for 1009  1453  cm  band t o the red o f t h e o r i g i n was  t h i s r e a s o n , was  u n u s u a l l y broad  t a k e n t o mark the p r e s e n c e o f the c o m b i n a t i o n 2 x 219  as w e l l as a p o s s i b l e  and N-H  bonds are not  +  fundamental.  A l t h o u g h v i b r a t i o n s composed e s s e n t i a l l y o f the s t r e t c h i n g of C-H  and,  the  expected t o appear i n the e l e c t r o n i c t r a n s i t i o n s  i n v o l v i n g the i r - e l e c t r o n s of the a r o m a t i c r i n g systems, the weak l i n e s 3081  and  3442 cm * t o the r e d of the o r i g i n p r o b a b l y mark t h e appearance of  t h e s e modes.  The  weakness o f the 3442 cm  can be o n l y q u i t e a s m a l l change i n the N-H  ^ i n t e r v a l indicates that  there  bond l e n g t h and p r o v i d e s  no  85 support f o r the suggestion  t h a t the p r o t o n o f t h e NH group t e n d s s t r o n g l y  towards i o n i c d i s s o c i a t i o n i n the e x c i t e d e l e c t r o n i c , s t a t e . F.  Assignment o f Fundamentals The  assignment of m o l e c u l a r fundamentals from i n f r a r e d and Raman  s p e c t r a i s based on t h e assumption t h a t the s t r o n g e s t must mark a f u n d a m e n t a l .  W i t h i n the group i n t r a - o r  l i n e i n any  inter-molecular  i n t e r a c t i o n s between the v i b r a t i o n a l s t a t e s i n v o l v e d may i n t e n s i t y d i s t r i b u t i o n s (the group o f l i n e s around 1300 the p r e v i o u s  s e c t i o n represents  group  lead to em  perturbed  * discussed  an example o f q u i t e a s t r o n g  intra-molecular  i n t e r a c t i o n ) but the above assumption i m p l i e s t h a t the observed s t r o n g c o r r e l a t e s w i t h the t r a n s i t i o n a l l o w e d i s recognized  appear o n l y weakly i n any  spectrum b u t , at l e a s t f o r the A^ f u n d a m e n t a l s , the e x p e c t a t i o n s t r o n g i n at l e a s t one  experiment.  I n any  event the s t r o n g  line  i n the absence o f p e r t u r b a t i o n s .  t h a t some fundamentals w i l l  t h e y w i l l be  in  one  i s that  of the t h r e e s p e c t r a a v a i l a b l e from l i n e s w i l l be a s s i g n e d  first.  It is  It  - 70 -  c l e a r t h a t fundamentals o f low i n t e n s i t y w i l l be t h e most d i f f i c u l t t o r e c o g n i z e u n l e s s t h e y a r e w e l l s e p a r a t e d from o t h e r l i n e s so t h a t any i n t e r a c t i o n s w i l l be s m a l l . Ai  Symmetry In t h e f l u o r e s c e n c e spectrum d i s c u s s e d i n t h e p r e v i o u s s e c t i o n , t h e  i n t e r v a l s 219, 427, 654, 888, 1009, 1151, 1287, 1336 and 1625 cm" r e p r e s e n t t o t a l l y symmetric f u n d a m e n t a l s .  certainly  The i n t e r v a l s 220, 431, 743, 860,  1015, 1107, 1291, 1455, 1483, 1576 and 1629 cm" the  1  1  i n t h e Raman spectrum and  l i n e s a t 221, 418, 751, 852, 910, 1006, 1109, 1136, 1200, 1284, 1327, 1442  and 1620 cm  1  i n t h e i n f r a r e d spectrum must a l s o mark f u n d a m e n t a l s .  f r e q u e n c i e s common t o t h e t h r e e s e t s above number s i x t e e n  The  and a r e e n t e r e d  i n T a b l e 13 as t h e s i x t e e n A^ fundamentals e x p e c t e d below 2000 cm .  The  1  888 cm  1  fluorescence i n t e r v a l i s associated with the i n f r a r e d l i n e at  910 cm  1  f o r the following reasons:  ( i ) the fluorescence i n t e r v a l of carba-  z o l e i n a b i p h e n y l m a t r i x (Appendix I ) o c c u r s a t 898 cm  1  and ( i i ) t h e  apparent f r e q u e n c y o f t h e i n f r a r e d l i n e i s i n c r e a s e d by t h e a d j a c e n t s t r o n g component o f t h e  l i n e a t 928 cm" . 1  I n t e r e s t i n g l y , t h e 654 cm  1  fundamental was a s s i g n e d from one o f t h e  s t r o n g e s t f l u o r e s c e n c e l i n e s w h i l e i t would have been e s p e c i a l l y t o make t h e assignment from t h e i n f r a r e d o r Raman spectrum. 1575 cm  1  difficult  S i m i l a r l y , the  fundamental was a s s i g n e d b e s t from t h e Raman spectrum and t h e 910  and 1200 cm  1  fundamentals from t h e i n f r a r e d  The c_ p o l a r i z e d  i n f r a r e d l i n e s a t 3084, 3077, 3055 and 3039 cm  t a k e n t o mark t h e f o u r C-H s t r e t c h i n g i n t e r v a l o f 3061 cm  spectrum.  1  fundamentals.  i s probably the A  1  are  The prominent Raman  f a c t o r group component o f t h e  m o l e c u l a r mode whose B^^ component l i e s a t 3055 cm f l u o r e s c e n c e l i n e a t 3081 cm  1  1  and t h e v e r y weak  probably c o r r e l a t e s with the i n f r a r e d  line  at 3084 cm  .  The N-H s t r e t c h i n g fundamental was observed a t about 3420 cm  i n t h e i n f r a r e d , 3421 cm  1  i n t h e Raman and 3442 cm  1  i n the fluorescence  spectrum. E> Symmetry 2  There i s l e s s i n f o r m a t i o n a v a i l a b l e t o d e t e r m i n e t h e and t h e assignment i s c o r r e s p o n d i n g l y escence spectrum  less certain.  fundamentals  However, from t h e f l u o r -  fundamentals were d e f i n i t e l y l o c a t e d a t 549, 616, 996,  1118, 1210, 1391, 1461, 1487, and 1607 cm" . 1  fundamental a t 1237 cm  The assignment o f a B  2  from f l u o r e s c e n c e r e s t s on t h e b a r e l y s i g n i f i c a n t  1  energy d i f f e r e n c e between t h e b_ p o l a r i z e d l i n e a t 1231 cm  1  and t h a t i n c_  p o l a r i z a t i o n a t 1237 cm . 1  Reliable B  2  fundamentals were observed as s t r o n g l i n e s i n t h e i n f r a r e d  spectrum a t 505, 616, 835, 995, 1158, 1233, 1320, 1380, 1452 and 1594 cm" . 1  F r e q u e n c i e s common t o b o t h s e t s number f o u r t e e n so t h a t two more fundamentals must be chosen from t h e somewhat l e s s i n t e n s e b p o l a r i z e d i n f r a r e d l i n e s a t 737, 1022, 1270, and 1694 cm" . 1  The l i n e a t 737 cm  1  i s not p a r t i c u l a r l y s t r o n g and f a l l s i n a r e g i o n  o f i n t e n s e a b s o r p t i o n p o l a r i z e d i n t h e ac_ p l a n e ; any c r y s t a l  imperfection  o r s t r a i n need o n l y be s l i g h t t o i n d u c e components o f t h e i n t e n s e i n t o t h e b_ a b s o r p t i o n spectrum.  lines  However, t h i s does n o t seem t o have o c c u r r e d  s i n c e t h e b_ p o l a r i z e d l i n e s do n o t c o i n c i d e i n energy w i t h t h o s e o f a or £ p o l a r i z a t i o n .  Because t h e l i n e a t 737 cm  1  i s the strongest of that  group i t i s t h u s t a k e n as a f u n d a m e n t a l , t h e l i n e s a t 756, and 772 cm"  1  presumably marking t h e p r e s e n c e o f c o m b i n a t i o n s . A l t h o u g h t h e r a t h e r b r o a d l i n e a t 1694 cm  1  must c o n t a i n  considerable  c o m b i n a t i o n a b s o r p t i o n , t h e problem i s t o d e c i d e whether o r not t h e r a t h e r  - 72 c o n s i d e r a b l e l i n e s t r e n g t h i s d e r i v e d from a f o r t u i t o u s c o i n c i d e n c e o f many c o m b i n a t i o n s a t t h a t energy.  The i n f r a r e d spectrum o f f l u o r e n e and o f  d i b e n z o t h i o p h e n e ( v i d e i n f r a ) show o n l y a number o f f a i r l y weak l i n e s i n t h i s r e g i o n and so the t e n t a t i v e c o n c l u s i o n i s reached t h a t t h e r e i s no s t r o n g fundamental a t 1694 cm .  A f r e q u e n c y as h i g h as 1694 cm  1  1  should  not be l i g h t l y d i s c a r d e d f o r i t s i n c l u s i o n i n a l i s t o f fundamentals would have a p r o f o u n d e f f e c t on any c a l c u l a t e d f o r c e The c h o i c e o f 1022 cm  1  as t h e l a s t  field.  fundamental was q u i t e a r b i t r a r y  and was based on t h e b e l i e f that the l i n e a t 1270 cm  1  as a c o m b i n a t i o n had  the g r e a t e r o p p o r t u n i t y t o . a c q u i r e i n t e n s i t y from the more numerous fundamentals nearby. Using  l i n e s t r e n g t h as t h e o n l y c r i t e r i o n , t h e f o u r C-H s t r e t c h i n g  fundamentals were a s s i g n e d order of p r o b a b i l i t y .  as 3050, 3030, 2940 and 3094 cm  The v e r y s t r o n g l i n e at 3050 c m  r e g i o n o f t h e spectrum and may  represent  -1  i n decreasing  dominates t h i s  a case o f n e a r degeneracy o f more  t h a n one f u n d a m e n t a l . B^ Symmetry The p r e s e n c e o f B^ fundamentals were observed i n t h e a_ p o l a r i z e d i n f r a r e d spectrum a t 148, 310, 438, 570, 720, 742, 924, and 1152 cm" . 1  The p o s i t i o n s  o f t h e l a s t two B^ fundamentals c o u l d not be e s t a b l i s h e d from t h e i n f r a r e d spectrum a l t h o u g h where s h o u l d e r s  i t i s p o s s i b l e t h a t one of the two c o u l d be near 880  cm"  appear i n the i n f r a r e d and Raman s p e c t r a .  A^ Symmetry Only one A„ fundamental was found at 299 cm  G.  1  from the Raman spectrum.  Normal C o o r d i n a t e C a l c u l a t i o n W i l s o n ' s GF m a t r i x method was  employed t o c a l c u l a t e the c a r b a z o l e  1  - 73 fundamental f r e q u e n c i e s .  The c a l c u l a t i o n s were performed on an IBM model  7044 computer u s i n g a somewhat m o d i f i e d v e r s i o n o f a n o r m a l - c o o r d i n a t e  program  88 w r i t t e n by S c h a c h t s c h n e i d e r . The G-matrix was c o n s t r u c t e d from t h e bond l e n g t h s and bond a n g l e s shown i n F i g . 7,. and t h e molecular, symmetry was used t o advantage i n d e r i v i n g t h e symmetry c o o r d i n a t e s r e q u i r e d t o f a c t o r t h e s e c u l a r e q u a t i o n .  The  redundant c o o r d i n a t e s were handled d i r e c t l y by t h e program. In-plane  calculation  F i g . 16  In-plane i n t e r n a l coordinate d e f i n i t i o n s o f carbazole  The  f o l l o w i n g v a l e n c e - t y p e p o t e n t i a l was used:  2V = z [ K R  j RJ  + 2F!J R.R  f/i  *  D  +  2  2  F  Ro- j j+1  + 2F*  rWl  f V'V'  ]  +  RmR.R. j j +_2+ *  2 F  2F!J R.R. ,]J  Rp j j+3  *Vj.ll  £3.3)  ~  The  f o r c e f i e l d was  74  t r a n s f e r r e d from phenanthrene  and  t h e r e f o r e the  symbolism u s e d by C a l i f a n o was  r e t a i n e d i n l a b e l l i n g the i n - p l a n e  internal  c o o r d i n a t e s shown i n F i g . 16.  I t s h o u l d be n o t e d t h a t , w i t h t h e C-C  bond  l a b e l l e d z by C a l i f a n o o f t h e phenanthrene m o l e c u l e removed, t h e s t r u c t u r e collapses i n t o that of carbazole.  The  correspondence between t h e  c o o r d i n a t e symbols i n t h e p o t e n t i a l energy e x p r e s s i o n and those  internal  i n F i g . 16  i s as f o l l o w s : Rj = t h C C o r CN bond s t r e t c h i n g c o o r d i n a t e s  q,riS,1,t,u,v,w  e  r.. = t h e CH and NH bond s t r e t c h i n g c o o r d i n a t e s = the ^  e  = t h e CCH  o,m,p The  a n g l e b e n d i n g c o o r d i n a t e s a, B,Y, <$, , C, 6,K ,T ,X,tn b e n d i n g c o o r d i n a t e s T,V,cr,*  = o r t h o , meta, p a r a , r e s p e c t i v e l y  l e t t e r s K,H,  and  F r e f e r r e s p e c t i v e l y t o the s t r e t c h i n g , b e n d i n g , and  i n t e r a c t i o n force constants. constants The  l i s t e d i n Table  Except f o r m i n o r v a r i a t i o n s , t h e f o r c e  11 were t r a n s f e r r e d d i r e c t l y from phenanthrene.  CC s t r e t c h i n g f o r c e c o n s t a n t s  bond l e n g t h and  o f phenanthrene were p l o t t e d a g a i n s t  from t h i s graph v a l u e s o f  bond l e n g t h s o f c a r b a z o l e . rather a r b i t r a r i l y  The  were found from the known  a n g l e b e n d i n g f o r c e c o n s t a n t s were a l t e r e d  i n an e f f o r t t o conform w i t h t h e s m a l l v a r i a t i o n  force constant with valence  a n g l e g i v e n i n r e f e r e n c e 73.  of  A l l other force  c o n s t a n t s were as d e f i n e d p r e v i o u s l y . The Table  13.  c a l c u l a t e d f r e q u e n c i e s are compared w i t h t h e observed v a l u e s i n  - 75 T a b l e 11  The i n - p l a n e f o r c e c o n s t a n t s o f c a r b a z o l e .  Type  F o r c e Constant  Value o  K„  5.07 mdyne/A  u  K  N H  K  c c  6.50 K  H„„„ CCC  7.00  r  K = K = K = K = K = K 1 q s t u w K v H = H = H = H. a. & y 6 H = H T  H  K  R  R  CNC H„ HCC r r  1.03  0.70  •  X  0.50  = H  0.55  TT  U  H , = H , HNC CC F ^ ortho CC  0.91  H e H = H, a  H  0.45  X r s 1 F = F = F = F q r s 11  F  = F  W  °- ° ° 0.80 mdyne/A 5  t q  1  0.07  W  F J £ ortho CN  q w t F = F v v F = F q w  F ^ meta CC  F s  t  U  0.61 0.61  U  q  F  r  w w F w  = F s  = F r  t  = F  1  w  1  = F  V  1  F?l meta CC  r  q  F = F u u V  F CC V ± para X  = F* = F t w  v  q  F q F'  r  SS  w  +  q  -0.32 -0.06  0.15 -0.12 0.15  t  u  = F t  -0.12  w  F  o  0.94 mdyne A 1.00  H  H  5.10  = H.. to = H  6  H  U ..  6.3  1  t = F, r == FF  t  u  0.30 -0.07  - 76 Type  Force Constant F  cc  0,.03  5  V  _CN F  F  p a r a  F  ccc  S  = F u  u  t  0,.03  1  -0,.07  u  F " = F s s  = l -V-  Y  CC  = F  't F  ccc  F  CN  F „HCC CC „HNC CN CCC CCC  F  = F  K  = F w  9  F  =  Y  r  F  =  6  r  F  t  = F  0.. 23 mdyne  t  0,.23  n  = F w  W  p  w  V  = F  0,.41  5  V  0,.23  n  u = F u  £  u  0,.41  8  F ° = F ° = F r r q F  = F  F  q  = F w  K  w  8  q  q T  y  = F s  y  = F s  11  -  V  = F/ = F  X t  a  0 .18 0..18  x  u  F  = F Y  Y  = F  T  K  D  Value  = F  a  = F  B  a  0  -0.049 mdyne/A  6  K  = F " = F  9  ?  =• F  5  = F  10  CCC CCN CH CH  0 .057  W  K  -0 .49 0.068 mdyne/A  Out-of-plane  calculation  The o u t - o f - p l a n e motions  a r e d e s c r i b e d by Y (CH wagging) and <P  ( t w i s t i n g o f carbon and hydrogen atoms about a C-C bond).  Thus t h e f o r c e  f i e l d w h i c h was p r e v i o u s l y g i v e n by W h i f f e n ^ may be e x p r e s s e d as  2V = P r £ y o j 2  +  2  2p r £y.y. . + 2p r E y . Y . _ + 2p r ^ Y . Y . o o j j+1 m o j j+2 p o j j+3 2  2  r  2  l  r  T  (3.4) + QR £<j> + 2q R E < M . , + 2t R r - Y . ( * . , 2  O  2  J  2  n  O  O  J  J+1  O O O  J  j-1  J  - 77 -  where P and Q a r e t h e d i a g o n a l f o r c e c o n s t a n t s , and p , p , p , q and t ^ • o m p o o are the i n t e r a c t i o n constants.  The e q u i l i b r i u m CC and CH benzene bond  l e n g t h s a r e denoted by t h e l e t t e r s R • J  and r . o o  The n u m e r i c a l v a l u e s o f t h e 86  f o r c e c o n s t a n t s f o r benzene t a k e n d i r e c t l y from W h i f f e n  and t h e v a l u e s o f  a m o d i f i e d s e t a r e l i s t e d i n T a b l e 12. T a b l e 12  P Q  Values o f t h e o u t - o f - p l a n e f o r c e c o n s t a n t s  Whiffen  Modified  .0.286  0.259  0.0290  Whiffen  Modified  0.012  0.011  > 0  1 m > P  0.015  -0.022  -0.020  -0.017  -0.015  The d i f f i c u l t i e s encountered  (10^ dyne/cm)  q o t o  Whiffen  Modified  -0.0100  -0.005  0.014  0.010  i n t h e t r a n s f e r o f t h e benzene f o r c e f i e l d 87  to anthracene b r i e f l y here. expected  by Evans and S c u l l y  were a l s o noted and a r e r e c o u n t e d  S l i g h t changes i n t h e f o r c e  constants associated with y  s i n c e t h e hydrogens i n the more complex m o l e c u l e s  environments. displacements  a r e  have d i f f e r e n t  F u r t h e r , t h e f o r c e c o n s t a n t s a s s o c i a t e d w i t h the independent o f t h e carbon atoms a t t r i g o n a l carbons where an i n t e r n a l  c o o r d i n a t e d e f i n i t i o n s i m i l a r t o y i s a p p l i c a b l e a r e unknown and a r e assumed t o have t h e same v a l u e as  y  I  n  t h e benzene c a s e , t h e i n t e r n a l  <ji a r e a l l e q u a l , however, i n a more complex m o l e c u l e <j> s d e p e n d i n g on t h e c o m b i n a t i o n 1  coordinates  there are a v a r i e t y of  o f carbon and h y d r o g e n atoms a t t a c h e d t o  t h e C-C bond about which t h e t o r s i o n i s t a k i n g p l a c e .  I t was assumed t h a t  a l l t h e t o r s i o n s were e q u a l , and were a c c o r d i n g l y a s s i g n e d t h e same v a l u e o f the f o r c e c o n s t a n t .  F i n a l l y , w i t h respect to the i n t e r a c t i o n constants,  t h e c o n v e n t i o n a p p l i e d t o benzene was adhered t o , t h a t i s , o n l y i n t r a - r i n g terms were t a k e n i n t o account.  I t was r e c o g n i z e d t h a t two- r i n g s may have  an i n t e r n a l c o o r d i n a t e i n common which w i l l r e s u l t i n an i n t e r - r i n g interaction. The c a l c u l a t e d o u t - o f - p l a n e f r e q u e n c i e s a r e compared w i t h t h e observed v a l u e s i n T a b l e 13.  T a b l e 13.  A comparison o f t h e observed  and c a l c u l a t e d fundamentals o f  carbazole.  Species  Observed  Calculated  Species  3421  3436  3084  3091  3094?  3091  3077  3068  3050  3068  3055  3046  3030  3046  3039  3024  2940  3024  1625  1648  1594  1635  1576  1612  1490  1623  1481  1535  1452  1539  1449  1491  1380  1511  1334  1419  1320  1431  1288  1388  1233  1424  1205  1302  1204  1296  1136  1240  1158  1252  1107  1213  1118  1226  1012  1133  1022?  910  1041  995  856  857  835  747  759  737 ?  658  629  616  620  425  409  548  559  220  233  505  472  B  Observed  Calculated  2  b  1152 1051 1001  b  847  - 79 -  Species  Observed  Calculated  Species  C a l c . 1° C a l c . 2  A  1088  939  1049  893  Calculated Calc.l  d  B  0  Calc.2  1089  1237  926  935  1046  973  880?  895  982  771  825  741  831  903  691  754  722  737  782  467  588  566  567  676  410  478  445  433  519  299  231  303  310  342  414  104?  106  147  222  290  108  134  2  989  Observed  139  The observed q u a n t i t i e s a r e means o f t h e f a c t o r group components where t h e s e a r e r e l i a b l y known. See t e x t f o r a more complete d i s c u s s i o n . C a l c u l a t i o n 1 f r e q u e n c i e s based on m o d i f i e d f o r c e c o n s t a n t s . 86 C a l c u l a t i o n 2 f r e q u e n c i e s based on W h i f f e n ' s force constants.  H.  Conclusion As e x p e c t e d ,  i n f o r m a t i o n was  i t i s o n l y i n the A^ symmetry b l o c k , where f a i r l y  a v a i l a b l e from i n f r a r e d , Raman and f l u o r e s c e n c e s p e c t r a ,  t h a t a f i r m assignment o f fundamentals was observed  and  complete  possible.  A comparison o f the  c a l c u l a t e d f r e q u e n c i e s i s shown i n T a b l e 13.  symmetry b l o c k s where even o n l y one  experimental  For  those  assignment i s u n c e r t a i n  o r m i s s i n g the comparison p r o v i d e s no t e s t o f t h e v a l i d i t y o f the f o r c e f i e l d s i n c e the o r d e r i n g of t h e observed example, i f 1694  cm  1  r e p l a c e s 737 cm  f r e q u e n c i e s g r e a t e r than 737 cm  1  1  fundamentals i s i m p o r t a n t : f o r  as a B  fundamental then a l l the  occupy a d i f f e r e n t p l a c e i n T a b l e 13  and  d  - 80 " the h o r i z o n t a l comparison becomes q u i t e d i f f e r e n t . The agreement between observed and c a l c u l a t e d f r e q u e n c i e s f o r the species i s s a t i s f a c t o r y . achieve  a better f i t .  No attempt was made t o m o d i f y t h e f o r c e f i e l d t o  I t i s o b v i o u s t h a t a f i t o v e r twenty one v i b r a t i o n s  p r o v i d e s no t e s t f o r a f i e l d w i t h a g r e a t e r number o f a d j u s t a b l e p a r a m e t e r s . However, i t i s t e m p t i n g t o assume t h a t the f o r c e f i e l d i s e s s e n t i a l l y c o r r e c t and t o use t h e c a l c u l a t e d f r e q u e n c i e s as a g u i d e t o complete the a s s i g n m e n t , when the 737 cm 1270 cm  1  1  fundamental would be r e p l a c e d by one at  (see e a r l i e r d i s c u s s i o n on t h i s p o i n t ) .  study i s c l e a r l y r e q u i r e d . of the tenth  A mere d e t a i l e d Raman  The c a l c u l a t i o n f u r t h e r p r e d i c t s t h e appearance  fundamental near 220 cm  1  where i t c o u l d v e r y e a s i l y be  obscured i n the i n f r a r e d and Raman by the s t r o n g A^ fundamental present  already  and makes more c r e d i b l e the s u g g e s t i o n t h a t the (ab) and  l i n e s a t 104 cm  1  represent  (be) Raman  an A^ f u n d a m e n t a l .  I t i s r a t h e r u n r e a s o n a b l e t o expect the approximate c a l c u l a t i o n s c a r r i e d out i n t h i s work t o g i v e an a c c u r a t e d e s c r i p t i o n o f the normal modes o f m o t i o n and t h i s i s e s p e c i a l l y t r u e i n the crowded energy r e g i o n above 1000 for  t h e A^ s p e c i e s .  The two s t r o n g e s t l i n e s i n t h e f l u o r e s c e n c e  i n v o l v e t h e A^ fundamentals at 220 and 658 cm . 1  cm  spectrum  S i n c e t h e s e modes occupy  a r e g i o n where t h e d e n s i t y o f v i b r a t i o n a l s t a t e s i s low t h e c a l c u l a t e d normal modes (shown i n F i g . 17) s h o u l d g i v e at l e a s t a q u a l i t a t i v e i d e a of the chang i n the geometry i n g o i n g t o the e x c i t e d e l e c t r o n i c s t a t e .  In the  lowest  energy e l e c t r o n i c a b s o r p t i o n system o f phenanthrene^"'''^ t h e t o t a l l y symmetric fundamental a t 674 cm strong f a l s e o r i g i n .  1  i n the upper e l e c t r o n i c s t a t e a c t s as a  There i s no e v i d e n c e t h a t the 658 cm  1  fundamental o f 27  c a r b a z o l e forms a f a l s e o r i g i n e i t h e r i n f l u o r e s c e n c e o r a b s o r p t i o n .  - 81 -  V  F i g . 17  -I  • = 233 cm."  C a l c u l a t e d normal c o o r d i n a t e s f o r two A, fundamentals o f carbazole Z/= 6 2 9 cm."-I  F i n a l l y , i t may be o f i n t e r e s t t o note t h a t s e v e r a l  of the v i b r a t i o n a l  l e v e l s o f c a r b a z o l e show u n u s u a l l y l a r g e f a c t o r group s p l i t t i n g s . w i t h a s p l i t t i n g g r e a t e r t h a n 10 cm parentheses): 1444  vibrations  (B„ ) ; and B  v  iu '  1  1  1  Those  a r e ( f a c t o r group symmetry symbols i n  431 ( A ) , 418 ( B ^ ) ; 1455 ( A ) , 1442 ( B ) ,  vibrations  l u  148 (B, ) , 127 (B„ ) ; 451 (B, ) , 438 (B, ). lu ' m lu 3u v  J  v  v  Thus any g i v e n v i b r a t i o n need not. appear a t t h e same f r e q u e n c y i n t h e Raman as i n t h e i n f r a r e d spectrum.  Further, t h i s also provides a useful  criterion 27  f o r t h e assignment o f fundamentals s i n c e from C r a i g ' s e a r l i e r transitions  arguments  t h a t a r e n o r m a l l y f o r b i d d e n b u t appear by i n t e n s i t y  have a s p l i t t i n g d e t e r m i n e d by t h e c o e f f i c i e n t o f m i x i n g .  stealing  Chapter 4 The A b s o r p t i o n Spectrum o f C a r b a z o l e  A.  i n a Fluorene M a t r i x  Introduction The spectrum o f c a r b a z o l e i n s o l u t i o n shows t h r e e g e n e r a l r e g i o n s o f o  absorption i n the quartz u l t r a v i o l e t :  a m o d e r a t e l y weak system near 3300 A o  ( f = 0.042) r u n n i n g i n t o a system o f medium s t r e n g t h near 2900 A ( f = 0.15) and f o l l o w e d by a s t r o n g e r and more complex system which p r o b a b l y c o n t a i n s two o  o  s e p a r a t e e l e c t r o n i c t r a n s i t i o n s a t 2550 A and 2300 A.  A photoselection  study o f t h e p o l a r i z a t i o n o f t h e a b s o r p t i o n bands o f c a r b a z o l e i n e t h a n o l (93°K) and c y c l o h e x a n e  (293°K) s o l u t i o n s a s s i g n e d t h e s e systems as s h o r t ,  l o n g , l o n g , and s h o r t a x i s t r a n s i t i o n s r e s p e c t i v e l y . A l a t e r magnetophotos e l e c t i o n study o f c a r b a z o l e i n a d i l u t e s o l u t i o n o f d i e t h y l e t h e r a t 77°K o  supported  o  t h e assignment o f t h e 3000 A and 2900 A as b e i n g  predominantly 85 91 92  s h o r t and long a x i s t r a n s i t i o n s r e s p e c t i v e l y . T h e o r e t i c a l s t u d i e s have r e c e n t l y been c a r r i e d out and a l l t h r e e p r e d i c t t h a t t h e  '"  lowest-energy  t r a n s i t i o n would be weak and p o l a r i z e d along*'-.the s h o r t - m o l e c u l a r a x i s (A^-*— A^) w h i l e t h e second s h o u l d be s t r o n g e r and l o n g - a x i s p o l a r i z e d ( E ^ " * ' — ^ ) ; as i s u s u a l , t h e c a l c u l a t e d i n t e n s i t i e s were somewhat  over-estimated. o  The p r e s e n t work i s concerned w i t h t h e weak 3300 A a b s o r p t i o n system of carbazole i n a fluorene matrix.  Single c r y s t a l s of fluorene provide a  v e r y u s e f u l m a t r i x f o r s t u d y i n g t h e p o l a r i z e d f l u o r e s c e n c e and a b s o r p t i o n  - 83 _  s p e c t r a o f m o l e c u l e s which have a b s o r p t i o n systems at wavelengths g r e a t e r o  than about 3000 A and which f u l f i l  the c o n d i t i o n s f o r the f o r m a t i o n o f a  30 substitutional solid solution with fluorene.  t h a t have been 68 83 s t u d i e d i n such a mixed c r y s t a l system w i t h f l u o r e n e i n c l u d e anthracene ' 41 76 93 phenanthrene ' , and pyrene ' . The e . s . r . spectrum o f the lowest t r i p l e t 94 s t a t e o f pyrene reported.  Molecules  95 '  added as an i m p u r i t y t o f l u o r e n e has a l s o been  The v a l u e o f f l u o r e n e as a m a t r i x r e s t s on the f a c t t h a t  c r y s t a l has h i g h symmetry. Each m o l e c u l e o c c u p i e s 57 an o r t h o r h o m b i c u n i t c e l l  short molecular  (C^,) i n  such t h a t the l o n g a x i s o f t h e m o l e c u l e c o i n -  cides w i t h the £ c r y s t a l a x i s . and  a special site  the  Thus the t r a n s i t i o n s a c t i v e a l o n g the  axes a r e c o m p l e t e l y  r e s o l v e d by the e x a m i n a t i o n  of  long any  c r y s t a l s e c t i o n c o n t a i n i n g t h e £ a x i s (see F i g . 6) i n p o l a r i z e d l i g h t . The  a b s o r p t i o n spectrum o f c a r b a z o l e i n b i p h e n y l  (see appendix I)  a l s o s t u d i e d , but i s not d i s c u s s e d h e r e s i n c e i t d i d not y i e l d any  was  additiona  i n f o r m a t i o n not a l r e a d y a v a i l a b l e i n the study o f t h e a b s o r p t i o n spectrum of carbazole i n fluorene. B.  The  Spectrum  The p o l a r i z e d a b s o r p t i o n spectrum o f c a r b a z o l e i n a f l u o r e n e m a t r i x i s shown i n F i g . 18 and the a n a l y s i s o f t h e spectrum i s s e t out i n T a b l e The  e l e c t r o n i c o r i g i n was  The  s t r e n g t h o f t h e o r i g i n as shown i n F i g . 18 i s reduced c o n s i d e r a b l y by  the o c c u r r e n c e  l o c a t e d as the o n l y resonance l i n e i n the spectrum  o f simultaneous  e m i s s i o n ; i n d e e d , by e x t r a p o l a t i n g back the  s h o r t Franck-Condon p r o g r e s s i o n s  i n the t o t a l l y symmetric f r e q u e n c i e s  218,  _1 1236  and perhaps 648  the most p r o b a b l e  cm  14.  i t i s o b v i o u s t h a t the o r i g i n r e p r e s e n t s by f a r  t r a n s i t i o n at these  energies.  - 85  T a b l e 14  The a b s o r p t i o n spectrum o f c a r b a z o l e i n f l u o r e n e a t about. 15°K.  //b  //c  Int  Remarks  29 691  s  origin  32  s  32', l a t t i c e  218  s  218,  A  418  m  418,  A  433  m  l 2 x 218 - 3  497  sh  see t e x t  512  ms  512,  B  2  574  m  574,  B  2  648  vs  648,  A  680  w  l 648 + 32  717  ms  717,  A  l  732  w  l 218 + 512 + 2  789  w  218 + 574 - 3  824  w  824,  B  ms  2* 218 + 648 - 2  s  921,  B  864 921 932  mw  2 218 + 717 - 3  983  s  983,  ms  l 989, B ; 418 + 574 - 3?  ms  983 + 3 2 - 1  1033  ms  1033,  B  1118  s  1118,  B  989 1014  A  2  2  vw  2 418 + 717 + 1  m  512 + 648  ms  218 + 983  vw  218 + 989 - 3  1236  vs  1236,  A  1296  i  s  l 1296, A j ? ; 2 x 648?  '1318  s  1318,  B  1336  m  2 218 + 1118  m  218 + 1236 - 3  m  1469,  1136 1159 1201 1204  1451 1469  B  2  -1  - 86  //b_  //c_  Int  1484  m  1484, B  m  218 + 2 x 648 - 3  s  1548, B  m  1551,  ms  648  1591  ms  1591, k  1629  m  648  m  648 + 9 8 9 - 1  mw  418 + 1236 - 1  w  648 + 1033 + 1  w  717 + 9 8 3 - 1  ms  648 + 1118 + 1  w  218 + 1591 - 2  w  574 + 1236 - 2  1848  mw  218 + 648 + 9 8 3 - 1  1882  m  648 + 1236 - 2  1915  w  218 + 717 + 983 - 3  1948  mw  717 + 1236 - 5; 3 x 648 + 4  1981  w  2 x 218  ms  218 + 648 + 1118  2012  w  2 x 648 + 717 - 1  2093  w  218 + 648 + 1236 - 9  w  921 + 1236 - 5  vw  218 + 3 x 648 - 3  w  648 + 1548 - 2  mw  983 + 1236 - 2  mw  989 + 1236 - 5  2239  w  648 + 1591 - 3  2276  w  2 x 648 + 983 - 3  w  418 + 648 + 1 2 3 6 + 5  2318  w  2 x 648 + 1033 - 9  2347  w  1118 + 1236 - 7  2413  ' w  1511 1548 1551 1566  1636 1653 1682 1699 1767 1807 1808  1984  2152 2159 2194 2217 2220  2307  '  Remarks  2  2  +921-3  +983-2  1551 - 6  218 + 648 + 1548 - 1  - 87 -  //b  //c  Int  '  Remarks  2434  w  218 + 983 + 1236 - 3  2465  w  2 x 1236 - 7  2495  vw  218 + 2 x 648 + 983  2530  mw  2 x 648 + 1236 - 2  2785  vw  1236 + 1551 - 3  2823  vw  1236 + 1591 - 4  2863  vw  648 + 983 + 1236 - 4  2883  vw  2 x 648 + 1591 - 4  •The p o s i t i o n o f t h e o r i g i n i s g i v e n i n cm d i f f e r e n c e s from t h e o r i g i n .  and a l l o t h e r e n t r i e s show  - 88 -  That t h e r e i s a p r o g r e s s i o n up t o t h e second o v e r t o n e i n the 648 cm fundamental i s u n c e r t a i n . too  The i n t e n s i t y o f t h e 1296 cm  1  i n t e r v a l seems  h i g h t o be t h e second member i n a p r o g r e s s i o n e s p e c i a l l y when the t h i r d  member i s f a i r l y weak.  Both assignments o f the 1296 cm  fundamental and as t h e o v e r t o n e o f t h e 648 cm  1  1  i n t e r v a l - as a  fundamental - a r e i n c l u d e d  i n T a b l e 14; i n t h e absence o f f u r t h e r e x p e r i m e n t a l e v i d e n c e the f i n a l c h o i c e i s l e f t open. The l i n e 1014 cm  1  t o t h e b l u e o f the o r i g i n was u n u s u a l l y b r o a d . The  i m p r e s s i o n g a i n e d from a c l o s e s t u d y o f enlargements t a k e n from the o r i g i n a l p l a t e s was t h a t the s i n g l e b r o a d l i n e had n e a r l y s p l i t  i n t o two and would  have done so i f t h e sample c o u l d have been f u r t h e r c o o l e d .  Since there i s  no r e a s o n a b l e assignment as a c o m b i n a t i o n f o r a second l i n e , t h i s the  p o s s i b l e p r e s e n c e o f an  electronic  fundamental a t 1014 cm  1  indicates  i n the e x c i t e d  state.  The 1469 cm  1  i n t e r v a l was not a s s i g n e d as t h e c o m b i n a t i o n 2 x 218 +  1003 s i n c e 217 + 1003 d i d not appear a t a l l .  The assignment as a c o m b i n a t i o n  i s o n l y r e a s o n a b l e i f some s o r t o f i n t e r a c t i o n w i t h the 1484 cm  1  funda-  mental i s assumed.  C.  Discussion The r e g i o n t o the immediate b l u e o f t h e o r i g i n was q u i t e d i f f u s e and  o n l y t h e 32 cm ment.  1  interval  e n t e r e d i n T a b l e 14 c o u l d be p i c k e d out f o r measure-  The g r e a t e r p o l a r i t y o f c a r b a z o l e l e a d s t o a l a r g e r b i n d i n g  energy  as i m p l i e d by t h e v e r y d i f f e r e n t m e l t i n g p o i n t s o f the two s o l i d s , v i z . the m e l t i n g p o i n t o f c a r b a z o l e i s 247°C and of f l u o r e n e i s 116°C.  Thus t h e r e  i s p r o b a b l y an a p p r e c i a b l e c o n t r a c t i o n i n the u n i t c e l l d i m e n s i o n s around  - 89 -  the s i t e o c c u p i e d by the c a r b a z o l e m o l e c u l e  and the t r a n s l a t i o n a l symmetry  i n the f l u o r e n e c r y s t a l i s l o s t a t the i m p u r i t y so t h a t k_ i s no l o n g e r a good quantum number.  The  d i f f u s e n e s s then i s c r e a t e d by t h e appearance  o f a l a r g e number o f weak l o c a l i z e d l a t t i c e modes t h a t r e t a i n o n l y i n the s i t e group and t h a t become  classification  a c t i v e because o f a s m a l l s h i f t i n  the e q u i l i b r i u m o r i e n t a t i o n i n the l a t t i c e on e x c i t a t i o n .  The v e r y h i g h  p o l a r i z a t i o n r a t i o l i m i t e d o n l y by e x p e r i m e n t a l m i s a l i g n m e n t  of c r y s t a l  and W o l l a s t o n axes i n d i c a t e s t h a t the s i t e symmetry i s p r e s e r v e d .  The  assumption i s made i n the i n t e r p r e t a t i o n o f the spectrum t h a t i t i s the a x i s o f the c a r b a z o l e m o l e c u l e  long  t h a t i s d i r e c t e d a l o n g c_ and not the s h o r t  o r normal a x i s . The p u r e e l e c t r o n i c o r i g i n was m a t r i x s o - t h a t the t r a n s i t i o n may 85 91 calculations.  '  p o l a r i z e d a l o n g the b_ a x i s o f the  be a s s i g n e d * A ^ o — i n  agreement w i t h the  92 '  The  second e x c i t e d s t a t e was  not  observed.  A c o r r e l a t i o n between fundamentals o f t h e ground and f i r s t e x c i t e d e l e c t r o n i c s t a t e s i s g i v e n i n Table 15. c_ p o l a r i z a t i o n as a s h o u l d e r combination  (see Table  o f low f r e q u e n c y  600  fundamentals i s v e r y i n c o m p l e t e . fundamental at, 497 cm corresponding  1  18).  497 cm I t may  1  i n t e r v a l occurred i n mark the presence o f a  B^ and A^ fundamentals but t h i s  i s considered u n l i k e l y s i n c e combinations fundamentals f a l l near 400 and  The  o f the c o r r e s p o n d i n g  possibility ground s t a t e  cm ; a d m i t t e d l y knowledge o f t h e A^ 1  The  a l t e r n a t i v e i s t o a s s i g n a B^  n e a r l y degenerate w i t h the one a t 512 cm  e n t r y i s made i n T a b l e  1  and  the  15.  There i s no l o n g p r o g e s s i o n i n any fundamental i n t h e a b s o r p t i o n spectrum so t h a t any change o f shape i n g o i n g between the two be s m a l l .  e l e c t r o n i c s t a t e s must  However, i f the normal c o - o r d i n a t e s a r e the same or n e a r l y t h e  - 90 -  T a b l e 15  C o r r e l a t i o n between f u n d a m e n t a l s - o f t h e ground and f i r s t e x c i t e d state of carbazole.  Species  A  l  Excited  State  cl  Ground S t a t e S p e c i e s  218,  s  219, vs  418,  m  427, m  648,  vs  654,  717,  ms  s  Ground S t a t e  2 505  vs  512,  ms  549,  ms  743, mw  574,  m  616,  m  856  824,  w  835  921,  s  996,  1009, 1107  1014?, ms  State  497?, sh  b  888, ms 983,  B  Excited  s  989?, ms 1033,  b  1151,  mw  1024,  mw  ms  s  b  w  1022? 1118, 1158  1118,  b  b  m  b  1210,  s m  1236,  vs  1287,  vs  1237,  1296,  s  1336,  vs  1320  1453,  mw  1318,  s  1391,  s  1482,  mw  1469,  m  1461,  m  b  1551,  m  1577,  vw  1484,  m  1487,  m  1591,  ms  1625,  s  1548,  s  1607,  s  When a v a i l a b l e , ground s t a t e d a t a were taken from the spectrum o f c a r b a z o l e i n a f l u o r e n e m a t r i x .  fluorescence  T h i s . l i n e d i d not appear i n the f l u o r e s c e n c e spectrum and t h e e n t e r e d was measured from the i n f r a - r e d and Raman s p e c t r a .  frequency  - 91 -  same i n the two e l e c t r o n i c s t a t e s , then t h e c o r r e l a t e d f r e q u e n c i e s  should  p l a y s i m i l a r r o l e s and have r e l a t i v e l y t h e same i n t e n s i t i e s i n t h e a b s o r p t i o n as i n t h e f l u o r e s c e n c e spectrum. case. (e.g. A  Some fundamentals a p p e a r i n g  T a b l e 15 shows t h a t t h i s i s not t h e  with appreciable i n t e n s i t y i n fluorescence  fundaments a t 888, 1204, 1453 and 1482 c m  a t 1237 cm *) have no c o u n t e r p a r t  and t h e B  - 1  0  fundamental  i n t h e a b s o r p t i o n spectrum w h i l e t h e  fundamentals a t 921, 824 and p o s s i b l y 989 and 497 cm  1  a r e much more prominent  i n a b s o r p t i o n t h a n t h e a s s o c i a t e d ground s t a t e fundamentals i n f l u o r e s c e n c e . Thus i t may be c o n c l u d e d  that while the molecular  geometry has undergone  l i t t l e change f o l l o w i n g t h e e l e c t r o n i c t r a n s i t i o n , t h e f o r c e - f i e l d h a s . The n a t u r e o f t h e change (and t h e c o r r e s p o n d i n g  change i n bond o r d e r )  could  perhaps be d e t e r m i n e d i f s u f f i c i e n t fundamentals c o u l d be found t o a l l o w a normal c o - o r d i n a t e a n a l y s i s t o be c a r r i e d o u t f o r t h e e x c i t e d e l e c t r o n i c state.  Chapter 5 U l t r a - v i o l e t Spectra of Benz[f]indan  A.  Impurity i n a Fluorene  Crystal  Introduction Unfortunately, commercially  of i m p u r i t i e s .  a v a i l a b l e f l u o r e n e c o n t a i n s a l a r g e number  For i n s t a n c e , the i n t e n s e b l u e f l u o r e s c e n c e i s caused by 96  anthracene present 37 been d e t e c t e d . present  as an i m p u r i t y  '  and t r a c e amounts o f d i b e n z f u r a n have  97 ''  o r not  97  There i s some doubt whether c a r b a z o l e i s a l s o  (see, f o r example r e f e r e n c e s 96>97) a l t h o u g h  t h i s may  vary  a c c o r d i n g t o the source Of s u p p l y . The f l u o r e s c e n c e and a b s o r p t i o n s p e c t r a o f f l u o r e n e i n v e r y d i l u t e 96 97 96 s o l u t i o n s are now r e l i a b l y known. ' Nurmukhametov and Gobov also r e p o r t e d the c o r r e s p o n d i n g  s p e c t r a o f t h e p u r i f i e d s o l i d f i n d i n g them  o c o n s i d e r a b l y r e d - s h i f t e d from 3015 i n the s o l i d .  S i n c e the f l u o r e s c e n c e l i n e s c o i n c i d e d w i t h those 98  by Barbaron and P e s t e i l , was  o  A i n an n-heptane s o l u t i o n t o 3209 A recorded  99 '  t h e R u s s i a n workers concluded  i n d e e d t h a t o f f l u o r e n e even though t h e r e was  the v i b r a t i o n a l i n t e r v a l s and  intensity pattern.  f l u o r e s c e n c e of f l u o r e n e c r y s t a l s at 4°K,  t h a t the spectrum  an a p p r e c i a b l e change i n In a l a t e r study o f the  B e n a r r o c h e ^ found the 1  fluorescence  e m i s s i o n t o be comprised o f two d i s t i n c t p a r t s ; a weak spectrum I w i t h i t s  o o r i g i n near 3051 Spectrum I I was  A and  o a s t r o n g spectrum I I h a v i n g  i t s o r i g i n at 3209 A.  a g a i n i n the one measured by Barbaron and P e s t e i l ,  Benarroche a t t r i b u t e d b o t h f l u o r e s c e n c e s p e c t r a I and  and  I I to f l u o r e n e .  - 93 P a r k e r , H a t c h a r d and J o y c e ^ 1  have r e p o r t e d t h a t t h e d e l a y e d f l u o r e s -  1  cence i s q u i t e d i f f e r e n t from t h e prompt f l u o r e s c e n c e o f a s o l u t i o n o f c a r e f u l l y p u r i f i e d fluorene i n ethanol.  Although  measured a t low r e s o l u t i o n , i t i s p r o b a b l e comes from b e n z [ f ] i n d a n  t h e i r spectrum was  that the delayed  fluorescence  impurity.  The purpose o f t h i s c h a p t e r  i s t o show t h a t t h e f l u o r e s c e n c e  spectrum  I I i n f a c t a r i s e s from b e n z [ f ] i n d a n which i s known t o be another p e r s i s t e n t i m p u r i t y i n commercial f l u o r e n e (see r e f e r e n c e 37 and c h a p t e r  2) and t o  p r e p a r e t h e way f o r t h e f o l l o w i n g c h a p t e r i n which some e x c i t e d e l e c t r o n i c s t a t e s o f f l u o r e n e are d i s c u s s e d .  Removal o f t h e b e n z [ f ] i n d a n from  commercial f l u o r e n e by c a r e f u l chromatography p r o v i d e s a c r y s t a l  having  o no d e t e c t a b l e a b s o r p t i o n above 3052 A even when t h e sample i s c o o l e d t o about 10°K, b u t i t does show a sharp b _ - p o l a r i z e d a b s o r p t i o n l i n e a t 32 789 cm i n an ab f a c e which i s n o t o b s e r v e d i n a s y n t h e t i c a l l y p r e p a r e d  sample.  T h i s i n d i c a t e s t h e p r e s e n c e o f y e t a n o t h e r u n s u s p e c t e d and unknown i m p u r i t y i n commercial f l u o r e n e which p r o b a b l y g i v e s r i s e t o t h e weak f l u o r e s c e n c e . , . 100 spectrum I r e p o r t e d by Benarroche.  B.  The Mixed C r y s t a l Systems As mentioned e a r l i e r , t h e f o u r f l u o r e n e m o l e c u l e s occupy s p e c i a l s i t e s  i n an o r t h o r h o m b i c u n i t c e l l h a v i n g • a  space group P nam  r  r  (D„ S . The m o l e c u l a r 2h 1 (  J  p l a n e o f symmetry c o n t a i n i n g t h e s h o r t i n - p l a n e a x i s and m o l e c u l a r  normal  c o i n c i d e s w i t h t h e ab c r y s t a l m i r r o r p l a n e so t h a t t h e long m o l e c u l a r  axis  i s e x a c t l y p a r a l l e l t o _c. The s t r u c t u r e o f t h e b e n z [ f ] i n d a n m o l e c u l e i s shown i n F i g . 1. the e l e c t r o n i c p r o p e r t i e s o f a s u b s t i t u t e d n a p h t h a l e n e a l t h o u g h  I t has  looked a t  - 94 -  i n t h i s way i t i s named r a t h e r awkwardly The m o l e c u l e i s assumed t o be p l a n a r w i t h  2,3~dihydro-lH-cyclopenta[b]naphthalene. symmetry, when t h e 69 normal  v i b r a t i o n s may be c l a s s i f i e d as i n d i c a t e d i n T a b l e 16.  In analyzing the  s p e c t r a we make t h e f u r t h e r a s s u m p t i o n t h a t t h e guest m o l e c u l e s u b s t i t u t e s for  a h o s t m o l e c u l e i n each o f t h e two m a t r i c e s used.  I t i s t o be expected  t h a t b e n z [ f ] i n d a n would occupy a s u b s t i t u t i o n a l s i t e i n f l u o r e n e s i n c e i t i s a p e r s i s t e n t i m p u r i t y t h a t i s q u i t e d i f f i c u l t t o remove h a v i n g  a shape and  o t h e r p h y s i c a l p r o p e r t i e s v e r y s i m i l a r t o those o f f l u o r e n e and o f a n t h r a cene a n o t h e r common i m p u r i t y . of benz[f]indan  I t i s c l e a r t h a t one o f t h e m o l e c u l a r  i s a l i g n e d w i t h t h e c_ a x i s o f t h e f l u o r e n e c r y s t a l  t h e l i n e s o f t h e a b s o r p t i o n spectrum a r e c o m p l e t e l y  axes since  p o l a r i z e d ; then the  above assumption i s e q u i v a l e n t t o t h e s u p p o s i t i o n t h a t i t i s t h e long a x i s o f t h e guest t h a t i s d i r e c t e d along c_ and n o t t h e s h o r t o r normal a x i s . However, t h e spectrum o f b e n z [ f ] i n d a n  i n a mixed c r y s t a l w i t h b i p h e n y l was  a l s o measured as a check. The  biphenyl c r y s t a l  5 4  ' ^ belongs t o the monoclinic  space group 2 ^ / ( C 2 ^ )  w i t h t h e two m o l e c u l e s i n t h e u n i t c e l l o c c u p y i n g s i t e s o f symmetry oriented-gas biphenyl  a  .  The  r a t i o o f a l o n g - a x i s p o l a r i z e d t r a n s i t i o n i n t h e be' f a c e o f  i s 1^:1 »= 1:2x10^ and o f a s h o r t - a x i s p o l a r i z e d t r a n s i t i o n i s  I : I • i= 23:1. The a x i s _c' i s t h e p e r p e n d i c u l a r K  p  t o t h e ab p l a n e .  n  - 95 T a b l e 16.  D i s t r i b u t i o n o f t h e fundamental v i b r a t i o n s o f m o l e c u l a r benz[f]indan .  2v (!)  ( R  y  A  i  A  2  .  *)  B  l  >  y)  B  2  E  C (z) 2  n  ° (yz) v  N 1  1  l  1  23  18  1  1  -l  -1  12  11  1  -1  -l  1  13  11  1  -1  l  -1  21  17  N i s t h e number o f fundamentals i n each symmetry s p e c i e s w h i l e n i s t h e number w i t h energy l e s s t h a n 2000 cm~l  C.  The A b s o r p t i o n  Spectrum 37  The a b s o r p t i o n spectrum o f b e n z [ f ] i n d a n i n s o l u t i o n  shows t h r e e  o  g e n e r a l r e g i o n s o f a b s o r p t i o n above 2000 A .  At low energy t h e r e i s a weak  o system (f=0.0108) b e g i n n i n g  a t 3200 A which runs i n t o a n o t h e r system o f  o medium s t r e n g t h (f=0.115) a t about 2800 A.  A t h i r d i n t e n s e system  (f=1.13)  o o c c u r s a t 2300 A.  These g e n e r a l f e a t u r e s a r e q u i t e analogous t o t h o s e o f  the spectrum o f n a p h t h a l e n e .  T h i s c h a p t e r i s concerned w i t h t h e weak  o system a t 3200 A, t h e o n l y one o f t h e t h r e e t o be seen b e f o r e c u t - o f f by t h e matrices  occurs.  The p o l a r i z e d a b s o r p t i o n spectrum o f b e n z [ f ] i n d a n i n a f l u o r e n e m a t r i x i s shown i n F i g . 19 and t h e a n a l y s i s o f t h e spectrum i s s e t out i n T a b l e 17.  T a b l e 17.  The  polarized absorption  //b  //c  spectrum o f b e n z [ f ] i n d a n  Int.  in  fluorene.  Remarks  -79  w  lattice  -48  mw  lattice  vs  origin  134  mw  l a t t i c e ; :s e e  text  190  m  190,  A;  text  250  m  250,  B  2  363  ms  363,  B  2  s  402,  A  x  510  ms  510,  B  2  536  m  536,  B  2  590  w  590,  A ? ; 190  704  vs  704,  A  725  w  see  text  vw  363+  770  w  770,  A  804  m  2 x  402  838  m  838,  A  848  m  848,  B;  874  ms  874,  B  905 '  vw  402  +  510 - 7  950  mw  250  +  704 - 4  vs  973,  Aj  mw  989,  A  31  158  402  759  973 989  -see  :  +402-2  x  1  402 - 6 x  :250  2  + 590  2  2  1048  m  1060  m  363  +  704 - 7  1087  w  363  +  725 - 1  1093  w  250  +  838 + 5  ms  402  +  704 - 5  1114  mw  1114,  1161  mw  2 x 402  vw  190  1101  1165  ^1048,  A  B  +  2  2  + 363 973 + 2  - 6  +  8?  - 98  //b  //£  _  Int.  Remarks  1207  m  510 +  704 - 7  1223  w  250 +  973  1234  mw  536 +.704 - 6  1259  m  1259,  B  2  1294  mw  1294,  B  2  1323  m  2 x 402 + 510 + 9  1334  mw  363 +  1381  vs  1381,  1408  s  2 x  1449  s  1449,  A  1481  m  510 +  973 - 2  1509  w  536 +  973  1523  mw  1523,  B  1545  mw  704 +  848 - 7  1572  m  704 +  874 - 6  a  The energy o f t h e e l e c t r o n i c o r i g i n i s i n cm are g i v e n as d i f f e r e n c e s from the o r i g i n .  A b s o r p t i o n around the e l e c t r o n i c p o l a r i zed  to  the l o s s o f t r a n s l a t i o n a l  o c c u p i e d by  cm  1  temperature  clearly  probably appear  due  symmetry i n the f l u o r e n e c r y s t a l at the s i t e molecule.  Apart from the o r i g :i n i t s e l f , 79  1  are assumed t o r e p r e s e n t  h i g h Franck-Condon a l l o w e d n e s s .  of t h i s p a r t i c u l a r  sample was  lines  cm" to t h e r e d  and  lattice  Although  the  e s t i m a t e d t o be about 25°X, the  l i n e s remained sharp h a v i n g an average w i d t h of about 5 cm The  2  l o c a l i z e d l a t t i c e modes t h a t may  the b e n z [ f ] i n d a n  an e s p e c i a l l y  +973+6  704  The d i f f u s e n e s s :i s  t o the b l u e of t h e o r i g i n ; t h e s e  modes h a v i n g  402  ;  and a l l o t h e r l i n e p o s i t i i  s t a n d out from t h i s r e g i o n o f d i f f u s e n e s s a t 48 and 134  A  or i g i n , a l t h o u g h complex, was  a l o n g t h e £ a x i s o f the m a t r i x  caused by t h e l a r g e number o f  1  973 - 2  1  .  l i n e 190 cm " t o t h e b l u e o f the o r i g i n appeared o n l y i n t h e  - 99 -  fluorene m a t r i x  (and not i n b i p h e n y l o r n_-heptane m a t r i c e s ) .  t o mark t h e p r e s e n c e o f an through  This i s taken  m o l e c u l a r fundamental t h a t i s induced  i n t e r a c t i o n s w i t h phonons o f t h e m a t r i x .  The 134 cm  1  t o appear  interval  c o u l d be g i v e n a s i m i l a r i n t e r p r e t a t i o n a l t h o u g h , i n t h i s c a s e , a sharp d i s t i n c t i o n between i n t r a - and i n t e r m o l e c u l a r modes i s p r o b a b l y n o t s i g n i ficant . The assignment o f t h e 590 cm  1  i n t e r v a l as an A^ fundamental was made  from i t s appearance i n t h e spectrum i n a b i p h e n y l m a t r i x . the assignment as a c o m b i n a t i o n was n o t observed.  In t h i s  was n o t t e n a b l e s i n c e t h e 190 cm  1  case, interval  A p a r t from t h i s f e a t u r e and from t h e f a c t t h a t b e n z [ f ] i n d a n  may a p p a r e n t l y occupy more t h a n one s i t e i n b i p h e n y l and n-heptane m a t r i c e s , the s p e c t r a a r e v e r y s i m i l a r .  F o r t h i s reason  t h e s p e c t r a ( a b s o r p t i o n and  fluorescence) i n fluorene only are given i n t h i s The 725 cm resonance.  1  i n t e r v a l i s thought t o r e p r e s e n t an example o f Fermi  The evidence  f a v o u r i n g t h i s p o i n t o f view i s t h a t ( i ) i t i s a  weak l i n e a d j a c e n t t o t h e p a r t i c u l a r l y corresponding  D.  thesis.  l i n e was observed  The F l u o r e s c e n c e  s t r o n g one a t 704 cm  and ( i i ) no  1  i n t h e f l u o r e s c e n c e spectrum.  Spectrum  The p o l a r i z e d f l u o r e s c e n c e spectrum o f b e n z [ f ] i n d a n i n f l u o r e n e i s shown i n F i g . 20 w i t h t h e a n a l y s i s i n T a b l e 18.  I t i s seen t h a t t h e f l u o r e s c e n c e  spectrum, l i k e t h e a b s o r p t i o n spectrum, i s v e r y n e a r l y c o m p l e t e l y although  expected,  in solid solutions.  t h i s behaviour  i s not o f t e n observed  polarized;  f o r aromatic  The one e x c e p t i o n i s t h e l i n e 1280 cm  1  molecules  to the red of  the o r i g i n and, i n T a b l e 18, t h i s has been i n t e r p r e t e d as a r i s i n g from an a c c i d e n t a l degeneracy.  - 100 T a b l e 18.  The p o l a r i z e d f l u o r e s c e n c e spectrum o f b e n z [ f ] i n d a n i n f l u o r e n e .  //£  //b  Int.  Remarks  31 158  vs  origin  200  mw  200, A^; see t e x t  25S  w  258,  B  2  399  m  399,  B  2  mw  409,  A  :  m  560,  B  2  750  s  750,  A  1  803  ms  803,  A  1  mw  897,  B  2  vw  200 + 750 - 2  vw  990,  mw  1018,  A  vw  1062,  B  2  vw  1122,  B  2  mw  399  mw  1158, A ; 409 + 750 - 1?  1195  w  399  1280  w  1280, B ; 258 + 1018 + 4?  vw  1280,  1305  mw  560  +750-5  1358  w  560  +803-5  1373  m  1373, A^; see t e x t  1398  vs  1398,  A  1454  m  1454,  A  1497  mw  2 x 750 - 3  409 560  897 948 990 1018 1062 1122 1146  -  1158  1280  B  2  +750-3 2  +803-7 2  A  x  1  :  1544  • mw  1575  .w  1598  mw  200 + 1398; 2 x 803 - 8  1765  w  750 + 1018 - 3  1774  vw  399 + 1373 + 2  1795  w  399 + 1398 - 2  750  +803-9  200 + 1373 + 2  - 101 -  //b  //c  Int.  1815  vw  803 + 1018 - 6  w  399 + 1454  1905  w  750 + 1158 - 3  1956  vw  803 + 1158 - 5  2143  m  750 + 1398 - 5  2198  m  803 + 1398 - 3;  2252  w  3 x 750 + 2; 803  w  897 + 1398 + 1  2413  vw  1018 + 1398 - 3  2554  vw  1158 + 1398 - 2  2792  mw  2 x 1398 - 4  2851  w  1398 + 1454 - 1  1853  2296  a  Remarks  -1 The energy o f t h e e l e c t r o n i c o r i g i n i s i n cm and a l l o t h e r l i n e p o s i t i o n s a r e g i v e n cm~l as d i f f e r e n c e s from t h e o r i g i n .  The l i n e 200 cm  1  t o t h e r e d o f t h e o r i g i n appeared o n l y i n f l u o r e n e  and i s a s s i g n e d as an manner t o t h e 190 cm  1  fundamental i n d u c e d by t h e m a t r i x i n an analogous l i n e i n t h e a b s o r p t i o n spectrum.  From an i n s p e c t i o n o f t h e f l u o r e s c e n c e spectrum a l o n e , t h e 1373 cm  1  i n t e r v a l may have been a s s i g n e d as an A^ c o m b i n a t i o n o f (unknown) nont o t a l l y symmetric fundamentals a c q u i r i n g i n t e n s i t y  t h r o u g h a Fermi r e s -  onance w i t h t h e Franck-Condon a l l o w e d fundamental a t 1398 cm . 1  were s o , t h e n t h e same i n t e n s i t y  I f this  r a t i o f o r t h e s e two l i n e s s h o u l d be 102  observed i n t h e Raman spectrum. Raman spectrum  Both l i n e s have been r e c o r d e d  i n the  ( t h e d a t a have been e n t e r e d i n T a b l e 19 where i t i s found  t h a t t h e l i n e a t 1375 cm reverse of the s i t u a t i o n  1  i s s t r o n g e r than t h e one a t 1394 cm \ t h e i n f l u o r e s c e n c e . T h e r e f o r e i t may be c o n c l u d e d t h a t  b o t h l i n e s mark t h e p r e s e n c e o f A^ f u n d a m e n t a l s .  102 -  ,  29  F i g . 20  E.  ,  0 0 0  29  !  500  !  3 0 0 0 0  30  !  500  3IOOO  Cm"  1  A m i c r o d e n s i t o m e t e r t r a c i n g o f t h e p o l a r i z e d f l u o r e s c e n c e spectrum o f b e n z [ f ] i n d a n i n f l u o r e n e a t about 15°K. The l i n e s marked I d e s i g n a t e f l u o r e s c e n c e from t h e i m p u r i t y w i t h a d o u b l e d o r i g i n a t 29 519 cm~l and 29 505 cm-1 (see t e x t ) . The o r i g i n was t r a c e d from a d i f f e r e n t exposure on t h e p l a t e .  Discussion S i n c e t h e a b s o r p t i o n and ' f l u o r e s c e n c e s p e c t r a were c o m p l e t e l y p o l a r i z e d ,  i t may be concluded  t h a t an a x i s o f t h e b e n z [ f ] i n d a n m o l e c u l e l i e s  the c_ a x i s o f t h e f l u o r e n e c r y s t a l . occupies  I f t h e assumption t h a t  along  benz[f]indan  a s u b s t i t u t i o n a l s i t e i n t h e l a t t i c e i s c o r r e c t t h e n t h e pure 1  electronic t r a n s i t i o n i s long-axis polarized  1  A ~ i — A^.  This i s a l s o the  e x p e c t e d assignment by analogy w i t h n a p h t h a l e n e where t h e weak, low-energy  _ 103 _  transition i s k n o w n ^ ' t o  be  •<—''"A . However, t h e spectrum o f t h e 2u g • 1  be f a c e i n a b i p h e n y l m a t r i x was measured almost c o m p l e t e l y  and t h e e l e c t r o n i c o r i g i n was  c_ p o l a r i z e d a g a i n c o n s i s t e n t w i t h t h e l o n g - a x i s assignment.  The f i r s t a b s o r p t i o n system was measured  o n l y about 1600 cm  the o r i g i n when complete a b s o r p t i o n by t h e m a t r i x o c c u r r e d .  1  beyond  The second  e l e c t r o n i c t r a n s i t i o n was not observed. A c o r r e l a t i o n between fundamentals o f t h e ground and f i r s t s t a t e i s presented  i n T a b l e 19.  and n-heptane m a t r i c e s  excited  Data t a k e n from t h e s p e c t r a i n b i p h e n y l  are a l s o i n c l u d e d f o r comparison although  i t should  be n o t e d t h a t t h e n-heptane sample was p o l y c r y s t a l l i n e so t h a t i n f o r m a t i o n concerning  l i n e p o l a r i z a t i o n was not a v a i l a b l e .  The c o r r e l a t i o n  between  the fundamentals o f t h e ground and e x c i t e d e l e c t r o n i c s t a t e s was based on the r e l a t i v e s t r e n g t h s o f l i n e s i n t h e f l u o r e s c e n c e and a b s o r p t i o n s p e c t r a , i t b e i n g assumed t h a t t h e f o r c e f i e l d s o f t h e m o l e c u l e i n t h e two e l e c t r o n i c s t a t e s a r e v e r y s i m i l a r ; t h e absence o f p r o g r e s s i o n s  i n t h e s p e c t r a show'  t h a t t h e r e can be o n l y v e r y s m a l l changes i n bond l e n g t h s i n the t r a n s i t i o n .  (and s t r e n g t h s )  V i b r a t i o n a l modes were g e n e r a l l y reduced i n energy  f o l l o w i n g t h e e l e c t r o n i c e x c i t a t i o n presumably because t h e e l e c t r o n was t r a n s f e r r e d from a b o n d i n g t o an a n t i - b o n d i n g a s m a l l d e c r e a s e i n t h e average f o r c e  o r b i t a l which l e d , i n t u r n , t o  constant.  102 Raman, d a t a  have a l s o been i n c l u d e d i n T a b l e 19.  Depolarization  r a t i o s were n o t a v a i l a b l e and t h e assignments were made by f i n d i n g t h e c l o s e s t energy f i t t o t h e f l u o r e s c e n c e d a t a .  However, t h o s e Raman-active  modes a s s i g n e d A^.symmetry by comparison w i t h the f l u o r e s c e n c e a n a l y s i s were, i n g e n e r a l , t h e s t r o n g e s t .  When a fundamental was a s s i g n e d  from t h e  a b s o r p t i o n and not t h e f l u o r e s c e n c e s p e c t r a , a Raman-active v i b r a t i o n w i t h a  - 104 somewhat g r e a t e r energy t h a n t h a t i n t h e e x c i t e d e l e c t r o n i c s t a t e was i n s e r t e d i n T a b l e 19; t h e few s p e c u l a t i o n s o f t h i s s o r t attempted some s u p p o r t from t h e f a c t t h a t t h o s e fundamentals  gain  assumed t o be  were  102 s t r o n g i n t h e Raman spectrum Raman i n t e r v a l s  w h i l e t h o s e t a k e n t o be  1577 and 1433 cm  1  were weaker.  The  may a l s o mark t h e p r e s e n c e o f A^ funda-  mentals because o f t h e i r r e l a t i v e l y g r e a t s t r e n g t h o f 6 and 5 a r b i t a r y . , . . . , 102 mcensity units, respectively. T a b l e 19.  C o r r e l a t i o n between fundamentals  o f t h e ground and f i r s t  excited  electronic states of benz[f]indan  Symmetry A^ Excited State  Ground S t a t e  Absorption i n Fluorescence i n . : — Fluorene B i p h e n y l n-heptane Fluorene B i p h e n y l n-heptane 190 m  200 mw  402 s  397 vs  590? w  586 w  704 v s  702 vs  770 w  765 w  396 vs  707 vs  409 mw  405 mw  971 vs  974 vs  194  (3)  407  (3)  647  (2)  750 s  748 s  747 s  738  (4)  803 ms  799 ms  797 s  813  (2)  843  (3)  838 in 973 v s  Raman  1018 mw  1021 mw  1016 mw  1014  (3)  1158 mw  1163 mw  1154 m  1171  (2)  1280 vw  1280 w  1272 m  1296  (3)  1373 m  1379 m  1370 s  1.373  (8)  1381 vs  1381 vs  1391 s  1398 vs  1396 vs  1393 vs  1394  (6)  1449 s  1444 vs  1445 s  1454 m  1456 m  1450 m  1457  (5)  - 105 -  Symmetry B Excited State  Ground S t a t e  Absorption i n — Fluorene B i p h e n y l n-heptane  Fluorescence i n Raman  :  Fluorene  Biphenyl  n-heptane  250 m  247 m  251 vw  258 w  258 w  363 ms  358 s  359 s  399 m  401 m  393 w  389 (1)  510 ms  509 s  509 m  560 m  562 m  555 mw  550 (4)  536 m  532 m  848 m  853 m  853 w  874 ms  873 ms  877 w  989 mw  996 mw  1048 m  1046 ms  1114 mw  1109 m  1259 m  1254 m  1294 mw 1523 mw  252 (2)  581 (1) 872 (1) 897 mw  903 mw-  906 vw  990 vw 1046 vw  1062 vw 1122 vw  1261 vw  1280 w  992 (2) 1067 mw  1063 w  Chapter 6 A Study of Some E x c i t e d S i n g l e t and E l e c t r o n i c States of  A.  Triplet  Fluorene  Introduction Although s e v e r a l experimental  89 98 99 100 ' ' ' and  91 104 theoretical '  analyses  o f t h e spectrum o f f l u o r e n e have been r e p o r t e d , no f i r m assignments f o r the 4-u m o l e c u l ie have i . been u A e x c i•t *e d i e l -e, c t r o n i•c s t *a t *e s o f * the made. has  centered  x. * dAMost i s c u s s i •o n 104,105,106  on the s o l u t i o n a b s o r p t i o n spectrum (see F i g . 22) which shows  t h r e e d i s t i n c t groups of bands i n t h e q u a r t z u l t r a v i o l e t .  The  moderately  o  i n t e n s e band n e a r 3000 A (f=0.053) i s f o l l o w e d by a s t r o n g e r more complex o•  r e g i o n o f a b s o r p t i o n at about 2600 A (f=0.361) and ° beginning  an even s t r o n g e r  106  n e a r 2300 A.  Piatt  has  suggested t h a t the l o w e s t - e n e r g y system  o f f l u o r e n e s h o u l d be c o r r e l a t e d w i t h the c o r r e s p o n d i n g carbazole  or of phenanthrene a l t h o u g h  different.  The  system  the band i n t e n s i t i e s are somewhat  lowest-energy t r a n s i t i o n i n carbazole  p h e n a n t h r e n e , ^ ' ' ' i s now  low-energy system o f  (Chapter 4)  and  known t o be d i r e c t e d a l o n g the s h o r t i n - p l a n e mole-  c u l a r a x i s i n agreement w i t h P i a t t ' s c o n t e n t i o n and t h i s lends s u p p o r t t o o  the i d e a t h a t the 3000 A band o f f l u o r e n e s h o u l d a l s o be s h o r t - a x i s p o l a r i z e d (^A^-t—*Aj1 . transitions  Other t h e o r e t i c a l s t u d i e s ^ (one l o n g and one  long-axis t r a n s i t i o n  (^B  1  have p r e d i c t e d two weak  s h o r t - a x i s p o l a r i z e d ) f o l l o w e d by a s t r o n g  ^A^).  S i n c e the c a l c u l a t e d t r a n s i t i o n s were  c l o s e l y spaced i n energy, the o r d e r i n g of the weak t r a n s i t i o n s depended  on  the approximations used. o  Two  a t t e m p t s t o measure the p o l a r i z a t i o n of the 3000A band have been  - 107 r e p o r t e d . U n f o r t u n a t e l y , experiments^  the c r y s t a l samples used i n t h e  were c o n t a m i n a t e d w i t h an i m p u r i t y  t o have been b e n z [ f ] i n d a n .  The  (see Chapter 5) shown  i m p u r i t y a b s o r p t i o n was  t h e red of t h e f i r s t f l u o r e n e band and  i t was  first  about 2000 cm  largely this  1  to  benz[f]indan  98-100 system t h a t was  measured  and  i n a d v e r t e n t l y a t t r i b u t e d to fluorene.  89 The  second d e t e r m i n a t i o n  i n v o l v e d a m a g n e t o p h o t o s e l e c t i o n study of  fluorene  at 77°K i n a d i l u t e d i e t h y l e t h e r s o l u t i o n , where t r a c e i m p u r i t i e s i n f l u o r e n e s h o u l d be u n i m p o r t a n t . t i o n technique  T h i s method u t i l i z e d a broad-band e x c i t a -  t h a t d i d not p e r m i t an independent measurement on each  o v i b r o n i c band.  The  3000 A system was  p o l a r i z e d , y e t t h i s r e s u l t was s h o r t - a x i s t r a n s i t i o n having  found t o be p r e d o m i n a n t l y  long-axis  i n t e r p r e t e d as a r i s i n g from an e l e c t r o n i c  strong v i b r o n i c coupling with a long-axis  t i o n at h i g h e r energy i n o r d e r t o r e m a i n i n agreement w i t h P i a t t ' s  transi-  earlier  correlation. The  aim o f t h i s work was  the a b s o r p t i o n and observations states.  t o d e r i v e as much i n f o r m a t i o n as p o s s i b l e about  fluorescence s p e c t r a , paying  p a r t i c u l a r a t t e n t i o n to  any  which might a i d t h e assignment of t h e low-energy e x c i t e d s i n g l e t  I t w i l l be seen t h a t such an assignment may  a t i o n o f the c r y s t a l B.  The  1.  S e l e c t i o n Rules  be made from an examin-  spectra.  Pure C r y s t a l S p e c t r a  Fluorene  J  four molecules i n a u n i t c e l l . ^ 3.  b  screw r o t a t i o n s C ~ , C~, 2, 3, and  16 (D„, ) h a v i n g  forms o r t h o r h o m b i c c r y s t a l s o f space group P r  to  i  n  a  m  v  2\\  J  a  The m o l e c u l e s are numbered so t h a t  the  c and  C~ performed on m o l e c u l e 1 g e n e r a t e m o l e c u l e s  4 respectively.  Each f r e e m o l e c u l e s t a t e g i v e s r i s e t o f o u r zero wave v e c t o r  crystal  - 108 -  f u n c t i o n s which form a b a s i s o f t h e i r r e d u c i b l e r e p r e s e n t a t i o n s f a c t o r group.  of the D 2h  The c o m b i n a t i o n s o f t h e l o c a l i z e d one s i t e e x c i t o n  having the c o r r e c t transformation a Y 3 Y  properties are:  *  2  = l/2(cb - *  2  =  1/2C*!  +  1  6  = 1/2(4,  Y  e  =  functions  1  1/2C*!  +  •  3  +  -  " *2  +  + *  "  2  Y  V  (6.1)  *3 *3  -V  The c r y s t a l s t a t e s c a n be f u r t h e r c l a s s i f i e d a c c o r d i n g  t o whether t h e f r e e  m o l e c u l e s t a t e from which t h e y a r e d e r i v e d i s symmetric o r a n t i s y m m e t r i c t o t h e s i t e group o p e r a t i o n  a  . The c o r r e l a t i o n o f t h e f r e e m o l e c u l e  w i t h t h e c r y s t a l s t a t e s were found from symmetry c o n s i d e r a t i o n s  states  and t h e r e s u l t s  are c o l l e c t e d i n T a b l e 20. T a b l e 20. The e x c i t e d - s t a t e c r y s t a l w a v e f u n c t i o n s and t h e i r i r r e d u c i b l e representations  i n t h e space group c o r r e l a t e d w i t h t h e f r e e m o l e c u l e  transitions. Free m o l e c u l e Molecular C r y s t a l w a v e f u n c t i o n s D2h f a c t o r group C r y s t a l • s e l e c t i o n r u l e s t r a n s i t i o n s f o r wavevector (k=Q) r e p r e s e n t a t i o n selection rules z_ x  A 1 B  A 1 l l  forbidden  Y  +  Y  A  i  lg 2u 3u  forbidden y  1A  1A  A «• A 1 1 B ,A 2  A  Y Y :  B  a l l o w e d //b. allowed //a  forbidden  t  I  forbidden  lu  B 2g 3g  a l l o w e d //c_ forbidden forbidden  - 109 -  Thus, a l o n g - a x i s t r a n s i t i o n i n t h e i s o l a t e d m o l e c u l e g i v e s r i s e t o no_ a b s o r p t i o n i n an ab c l e a v a g e  p l a n e and a s h o r t - a x i s t r a n s i t i o n g i v e s  a b s o r p t i o n o n l y i n t h e ab p l a n e w i t h an o r i e n t e d - g a s 2.  ratio  ( f ^ / f ^ ) o f 2:1.  C r y s t a l Energies U s i n g t h e a l r e a d y enumerated c r y s t a l w a v e f u n c t i o n s as t h e b a s i s s e t ,  then t o a f i r s t order o f approximation, r s t a t e s w i t h r e s p e c t t o [w  we can express  the energies o f the  r + D ] ( t h a t i s , t h e sum  o f the f r e e molecule  t r a n s i t i o n energy and t h e change i n b i n d i n g energy o f a m o l e c u l e i n a c r y s t a l upon e x c i t a t i o n ) as f o l l o w s :  A* CD  =  z'i  •  T  A E * ( r ) = Z'l  n  E  AE^(r) = l < ?  The  +  u  - n\  2  z'l^  =  ( r )  n  - ZiJ  n  zij  T  - U\  T  A 6  n  + H [  2  ZlJ  +  2  3  3  -  3  4  i f ^  +  3  - EI-  zi^  +  +  ZiJ  ZiJ  (6.2)  4  4  i n t e r m o l e c u l a r resonance energy i s summed over t h e s e t s o f m o l e c u l e s  i n d i c a t e d by t h e second s u b s c r i p t s and r = y_ o r z depending on whether the f r e e molecule t r a n s i t i o n i s long o r s h o r t - a x i s p o l a r i z e d . 3.  Calculation o f the Crystal S p l i t t i n g s ;  Dipole-Dipole  Approximation. C a l c u l a t i o n o f the c r y s t a l s t a t e energies requires the e v a l u a t i o n of t h e i n t e r m o l e c u l a r c o u p l i n g energy between i d e n t i c a l m o l e c u l e s k and 1 w i t h -  ground s t a t e s  0  0  ^  X I *  and e x c i t e d s t a t e s t,^, t ^ .  The m a t r i x elements have  the.form r J  o ri,,  r  ir o.  k i ^hWiKh" =  ' ,, _..  -  (6  3)  - no The o p e r a t o r i s t h e i n t e r m o l e c u l a r p o t e n t i a l  2  '2  energy  +2  e2  2  Z^e e V e (6.4) r • f • g r f g f.l g.i— i,J f g r,.. • ' r . r . . • r,. fj gi i j tg where f , g a r e t h e n u c l e i , Z^ and Z t h e n u c l e a r c h a r g e s , and i and j t h e V, , kl  = -  2  1  2  +  z  2  3  , J  >  J  e l e c t r o n s o f t h e k t h and 1 t h 'molecules r e s p e c t i v e l y . e v a l u a t e t h e i n t e g r a l 1 ^ i s t o expand t h e o p e r a t o r multipoles.  i n a series of point  T h i s method has t h e advantage t h a t t h e m o l e c u l a r w a v e f u n c t i o n s  need n o t be s p e c i f i e d . the  One method used t o  The f i r s t n o n - v a n i s h i n g term i n t h e e x p a n s i o n g i v e s  p o t e n t i a l energy o f i n t e r a c t i o n i n t h e form  V  - V  k l =2)4 E  kl  r  ( " k ^ C V  r )]  k l  where M, and M, a r e t h e f r e e m o l e c u l e t r a n s i t i o n moments. -k —1 of  (6.5)  k l  The f i n a l  t h e e x p r e s s i o n used i n t h e program f o r computing the d i p o l e  form  interaction  sum i s  S  l  k l  =  ^4-  *kl  V r  (Q -I k  k l  )(Q .r t  k l  )]  (6.6)  k l  where M = eQ ( e l e c t r o n i c charge t i m e s t r a n s i t i o n l e n g t h i n c e n t i m e t e r s ) has been s u b s t i t u t e d i n t o equationft-S^The v a l u e o f Q i s r e l a t e d t o t h e o s c i l l a t o r s t r e n g t h f a t t h e energy v ( i n cm ) and can be o b t a i n e d from 1  solution  i n t e n s i t y measurements  f = 1.085 x 1 0 Q n  2  v  (6.7)  - Ill -  Equation  (6.6) was used t o compute t h e d i p o l e - d i p o l e i n t e r a c t i o n sums f o r  f l u o r e n e from c r y s t a l s t r u c t u r e d a t a  f o ra unit transition dipole  o length  (Q = 1) over a sphere o f 40 A r a d i u s .  The r e s u l t s a r e l i s t e d i n  T a b l e 21. T a b l e 21.  D i p o l e - d i p o l e i n t e r a c t i o n sums f o r c r y s t a l l i n e f l u o r e n e over a ° a b sphere o f 40 A r a d i u s f o r u n i t t r a n s i t i o n moments. '  k  >*  Z I  kl  1,1  -703  1,2  -2405  1,3 1,4  E I  kl  E I  kl -1602  2305 -4310  -907  -196  1077  178  -545  -1095  -550  x,y,z a r e t h e m o l e c u l a r axes shown i n F i g . 6 and l a b e l t h e d i r e c t i o n o f t h e t r a n s i t i o n moment c o n n e c t i n g t h e ground s t a t e w i t h t h e e x c i t e d s t a t e under c o n s i d e r a t i o n . b  C r y s t a l d a t a , D.M. 200 (1955).  Burns and J . I b a l l ,  P r o c . Roy. Soc. (London) A227  An e s t i m a t e o f t h e c r y s t a l t r a n s i t i o n e n e r g i e s and  associated with the long-  s h o r t - a x i s p o l a r i z e d t r a n s i t i o n s o f the f r e e molecule w i l l a s s i s t i n  the i n t e r p r e t a t i o n o f t h e e x p e r i m e n t a l  r e s u l t s d i s c u s s e d i n t h e next s e c t i o n .  o The  o s c i l l a t o r s t r e n g t h o f t h e 0-0 band o f t h e 3000 A a b s o r p t i o n system i n  f l u o r e n e s o l u t i o n was e s t i m a t e d  t o be 0.02 g i v i n g a t r a n s i t i o n d i p o l e l e n g t h  o o f 0.237 A.  The c a l c u l a t e d p o s i t i o n s o f t h e f l u o r e n e c r y s t a l l e v e l s f o r t h e  o t r a n s i t i o n d i p o l e lengths  1.0 and 0.237 A a r e g i v e n i n T a b l e 22.  of t h e c a l c u l a t i o n a r e d i s p l a y e d g r a p h i c a l l y i n F i g . 21.  The r e s u l t s  112  5 0 0  B  2g  4 0 0  300  H  B  |  u  ( / /  £  )  200 H O  -  o  100  H  _/  B  B  B 3<  3  B  A  (//b)  o  ig 3  u  ( / / g )  g  -200  Fig.  21.  F a c t o r group s p l i t t i n g s a s s o c i a t e d w i t h t h e l o n g - and s h o r t - a x i s  o o f f l u o r e n e m o l e c u l e c a l c u l a t e d f o r t r a n s i t i o n moments o f  0.237 A.  - 113 -  T a b l e 22.  Crystal level  Calculated crystal  levels  of fluorene  S h o r t - a x i s assignment Q = 1.0 Q = 0.237  L o n g - a x i s assignment Q = 0.237 Q = 1.0  AE (r)  -2881  -161  '-2023  -103  AE (r)  -1423  -80  4443  249  AE (r)  33  2  8787  492  AE (r)  -2137  a  P  6  £  4.  Room Temperature  -120  -1987  -101  Absorption  WAVELENGTH ( A ) 2200  24CO  — i —  4 0  4 2  4 4  46  W A V E N U M B E R ( k K )  F i g ,  The room-temperature a b s o r p t i o n s p e c t r a o f f l u o r e n e : f u l l c r y s t a l s e c t i o n //b_; d o t t e d solution  l i n e , ab  l i n e , ab c r y s t a l s e c t i o n //a_; b r o k e n l i n e  spectrum i n i s o - o c t a n e  (taken from " C a t a l o g u e o f U l t r a v i o l e t  Spectrograms" American P e t r o l e u m I n s t i t u t e ) .  The  114 -  a b s o r p t i o n spectrum a t 295°K i s shown i n F i g . 22.  The  thin, single  c r y s t a l s needed c o u l d o n l y be grown by s u b l i m a t i o n i n a f l o w o f n i t r o g e n e n t r a i n e r gas, when f l a k e s w e r e -  produced i n which the prominent ab  c l e a v a g e p l a n e i s the w e l l - d e v e l o p e d  face.  C r y s t a l t h i c k n e s s e s were  measured w i t h a Berek compensator once t h e r e f r a c t i v e i n d i c e s had been 107 d e t e r m i n e d by i n t e r f e r o m e t r y ;  the b i r e f r i n g e n c e was  found t o be 0.097  o  a t 4500 A.  The  curves  shown i n F i g . 22 r e p r e s e n t t h e mean v a l u e s o f d a t a  o b t a i n e d from f o u r c r y s t a l s whose t h i c k n e s s e s ranged from 0.5 The  e r r o r s p a n n i n g t h e s e s e p a r a t e measurements i s about 20%,  t o 2.5  u.  probably  a r i s i n g from r a p i d s u b l i m a t i o n o f t h e t h i n c r y s t a l s and from s t r a y l i g h t w i t h i n the monochromator f o r t h e t h i c k e r samples. efficients  fr , e, and e j i n t h e c r y s t a l a r e d e f i n e d so t h a t 3e a  v  Ca £  +  e  b  M o l a r e x t i n c t i o n co-  b  c  , ..  =  solution  3  c>"  +  E  I t s h o u l d be noted t h a t the o r i e n t e d - g a s  e s t i m a t e f o r the i n t e n s i t y  the c - p o l a r i z e d o r i g i n i s about 27,000 1 mole *cm t i o n i n t h e s u b l i m a t i o n f l a k e may  of  thus the l a c k o f absorp-  be g i v e n the f o l l o w i n g i n t e r p r e t a t i o n .  The m o d e r a t e l y i n t e n s e and s t r o n g t r a n s i t i o n s observed i n the s o l u t i o n o  o  spectrum a t about 3000 A and  2600 A must b o t h be p o l a r i z e d a l o n g the  a x i s o f the m o l e c u l e and may  be a s s i g n e d  t i o n observed at about 35 520 cm a t about 36 700  cm  p o l a r i z e d and may 35 520 cm  1  1  1  ^T^ <- ^A^.  i n the s o l u t i o n spectrum, i s t h e r e f o r e s h o r t - a x i s  be a s s i g n e d  *A^ <- ^A^.  The  a b s o r p t i o n induced f/8).  few weak bands t o the r e d o f  mark the appearance o f n o n - t o t a l l y  symmetric v i b r a t i o n s b u i l t on t h e l o w e s t - e n e r g y 1  The v e r y weak t r a n s i -  i n the s u b l i m a t i o n f l a k e and p o s s i b l y  i n the c r y s t a l spectrum may  about 33 050 cm  long  i n <c p o l a r i z a t i o n or they may  e l e c t r o n i c t r a n s i t i o n at represent ^ - p o l a r i z e d  t o appear by t h e convergence o f t h e i n c i d e n t beam (about  - 115 -  This experimental  assignment agrees w e l l w i t h Hummel and Ruedenberg's  intra-ring approximation, ^ 1  and Wait.  91  b u t d i s a g r e e s w i t h t h e c o n c l u s i o n s o f Pinkham  89 I t c o n f i r m s t h e r e s u l t o b t a i n e d by S i e g e l and J u d e i k i s but  shows t h a t t h e i r i n t e r p r e t a t i o n i s i n c o r r e c t . o  The  p o s s i b i l i t y t h a t e i t h e r one o r b o t h o f t h e bands a t 3000 A and  o  2600 A i s s h o r t - a x i s p o l a r i z e d w i t h t h e t r a n s i t i o n i n t h e c r y s t a l c a l l y b l u e s h i f t e d cannot be i g n o r e d . the p r e c e d i n g and  Recognizing  dramati-  that the calculation i n  s e c t i o n p r o v i d e s o n l y a rough e s t i m a t e o f t h e c r y s t a l  shift  s p l i t t i n g f o r t h e s h o r t a x i s a s s i g n m e n t , we c o n c l u d e t h a t t h e s t r o n g e r  b _ - p o l a r i z e d component i s expected t o show no s o l v e n t s h i f t where as t h e weak a - p o l a r i z e d component i s s l i g h t l y r e d - s h i f t e d , by O  3000 A  about 100 cm j  system and by somewhat l e s s than 1000 cm  f o r the  1  o  f o r t h e 2600 A system.  One f u r t h e r experiment was performed t o t e s t t h e above i n t e r p r e t a t i o n o f t h e l i n e a t 33 050 cm  1  as b e i n g c - p o l a r i z e d .  The u n p o l a r i z e d spectrum  o f a f l u o r e n e powder ground between f u s e d s i l i c a d i s c s was r e c o r d e d Cary 14 s p e c t r o p h o t o m e t e r .  on a  Some powder g r a i n s were expected t o be o r i e n t e d  so t h a t t h e e l e c t r i c v e c t o r o f t h e i n c i d e n t l i g h t would have an a p p r e c i a b l e p r o j e c t i o n a l o n g t h e £ a x e s , even though most g r a i n s may t e n d t o become a l i g n e d w i t h t h e i r prominent ab c l e a v a g e p l a n e s p a r a l l e l t o t h e r e t a i n i n g s i l i c a surfaces. o  The r e s u l t was t h a t t h e r a t i o o f t h e o p t i c a l d e n s i t i e s a t  o  2820 A t o 3020 A changed from 7.0 f o r t h e s u b l i m a t i o n f l a k e (see F i g . 22) t o 2.3 f o r t h e powder, a g a i n c o n s i s t e n t w i t h t h e above assignment. The  onset o f a b s o r p t i o n i n t h e ab p l a n e above 42 000 cm  1  suggests t h e  p r e s e n c e o f a s t r o n g , s h o r t - a x i s p o l a r i z e d t r a n s i t i o n near 45 000 cm . 1  " 116 " 5.  A b s o r p t i o n a t Low Temperature  i 3 3  F i g . 23  —  1  O O O  3 4 0 0 0  3 5  O O O  3 6  The a b s o r p t i o n s p e c t r a o f f l u o r e n e a t l i q u i d h e l i u m  O O O  temperatures  (a) i n an n-heptane m a t r i x , and (b) f o r b_ p o l a r i z a t i o n i n an ab crystal section.  The energy s c a l e r e f e r s o n l y t o t h e c r y s t a l spectrum.  The p o l a r i z e d a b s o r p t i o n spectrum o f a s u b l i m a t i o n f l a k e a t about 6°K i s shown i n F i g . 23.  The l i n e a t 35 524 cm  the weak ^A^—• "*"A^ t r a n s i t i o n .  1  i s assigned  as t h e o r i g i n o f  The weaker l i n e s t o t h e r e d a r e a s s o c i a t e d  w i t h n o n - t o t a l l y symmetric v i b r a t i o n s b u i l t on a £-polarized o r i g i n a t lower energy (see T a b l e 23); no f a c t o r group s p l i t t i n g was d e t e c t e d 2 vibrations. '  i n the  n  ab spectrum c o n s i s t e n t w i t h t h e i n v o l v e m e n t o f  The room  - 117 -  temperature spectrum had i n d i c a t e d t h e p r e s e n c e o f weak a b s o r p t i o n a t 33 050 c m  - 1  (see F i g . 22) which was a l t o g e t h e r absent i n t h e low-temperature  spectrum (where t h e a c c e p t a n c e a p e r t u r e was f/30) so t h a t t h i s may mark t h e p o s i t i o n o f t h e c_-polarized o r i g i n .  To check t h i s p o s s i b i l i t y a s u b l i m a t i o n  f l a k e 2.6 y t h i c k was mounted i n t h e h e l i u m c e l l so t h a t t h e ab p l a n e o f t h e c r y s t a l was i n c l i n e d 45° t o t h e i n c i d e n t beam.  T h i s arrangement  e x p e c t e d t o i n d u c e some c - p o l a r i z e d i n t e n s i t y i n t o t h e spectrum. l i n e was found a t 33 039 cm  1  was A sharp  and t h i s i s a s s i g n e d as t h e c - p o l a r i z e d  origin  o  o f t h e 3000 A system; t h i s l i n e was not. p r e s e n t i n t h e spectrum o f a s u b l i m a t i o n f l a k e ' 6 . 1 V- t h i c k mounted normal t o t h e o p t i c a l  train.  An e x a m i n a t i o n o f t h e c - p o l a r i z e d spectrum c o u l d o n l y be made from a melt-grown c r y s t a l .  A  be s e c t i o n was c u t from an i n g o t grown i n a Bridgman  f u r n a c e . U n f o r t u n a t e l y , t h e c r y s t a l was o n l y s l i g h t l y l e s s t h a n 1 mm  thick  (about 10^ t h i c k e r than r e q u i r e d ) and complete a b s o r p t i o n o c c u r r e d a t a l l o  wavelengths below 3046 A, a l t h o u g h t h e c u t - o f f i n c_ p o l a r i z a t i o n was about 60 cm  1  to the. r e d o f t h a t i n b_ p o l a r i z a t i o n .  As w e l l as t h e many sharp l i n e s l i s t e d i n T a b l e 23 t h e r e were d i f f u s e bands a t 33 379, 33 280, 33 215, 33 163 and p o s s i b l y a t 32 910 cm" , t h e l a s t 1  b e i n g e x t r e m e l y weak.  Any v i b r a t i o n a l s t r u c t u r e b u i l t on t h e s e broad  bands was l o s t beneath t h e more prominent sharp l i n e s a t h i g h e r energy. The b r o a d l i n e s presumably a r i s e from a d i s o r d e r e d r e g i o n o f t h e c r y s t a l , p o s s i b l y the c r y s t a l 6.  surface.  F l u o r e s c e n c e a t Low  Temperature  The f l u o r e s c e n c e spectrum from a be s e c t i o n a t about 15°K i s shown i n F i g . 24.  C a r e f u l s c r u t i n y o f t h e p h o t o g r a p h i c p l a t e r e v e a l e d t h a t what  appeared t o be broad bands at f i r s t g l a n c e , were i n f a c t about t h r e e ,  118 -  b-axis  — i  31500  1  1  32 COO  32500  1 —  33000  wavenumber (cm ) -1  F i g . 24  The f l u o r e s c e n c e s p e c t r a o f f l u o r e n e a t 15°K f o r a be s e c t i o n o f the s i n g l e c r y s t a l  (above) and i n an n-heptane m a t r i x  overlapping, rather d i f f u s e lines.  The c e n t e r s o f t h e band envelopes were  measured and i n s e r t e d d i r e c t l y on t h e spectrum i n F i g . 24. o r i g i n a t 32 818 cm  1  (below).  The f l u o r e s c e n c e  i s c o m p l e t e l y p o l a r i z e d along t h e c_ a x i s .  Other  bands appear 201 (m), 402 (m), 735 ( s ) , 995 (m), 1221 (m), 1527 (w) and 1589 c m " ^ ) 1  from t h e o r i g i n and are more n e a r l y d e p o l a r i z e d , a l t h o u g h as s t r o n g i n c t h a n i n b_ p o l a r i z a t i o n .  The  at l e a s t  p o l a r i z a t i o n of the  twice  fluorescence  bands, t h e n , i s c o n s i s t e n t w i t h t h e *B -s—^A^ assignment. According  t o the rough c a l c u l a t i o n f o r the l o n g - a x i s assignment o f  o t h e 3000 A system, the A^ and  B  f a c t o r group components ( i n a c c e s s i b l e  from the ground s t a t e d i r e c t l y ) are p r e d i c t e d a t lowest level  (on w h i c h the a l l o w e d  about 350  cm  and the B  1  energy.  c-polarized t r a n s i t i o n terminates) about 600 cm  1  t o h i g h e r energy.  The i s expected  The  weak-  zg c o u p l i n g l i m i t was  assumed i n a r r i v i n g at t h e above e s t i m a t e s but t h i s  not e x p e c t e d t o cause any i m p o r t a n t The  change i n the o r d e r i n g o f the  f l u o r e s c e n c e o r i g i n i n the ordered  was  levels.  c r y s t a l should i n v o l v e a consider-  a b l e a c t i v a t i o n energy. The  fluorescence probably  o r i g i n a t e s from the same d i s o r d e r e d p a r t o f  t h e c r y s t a l t h a t g i v e s r i s e t o the broad a b s o r p t i o n bands l i s t e d  earlier.  Pronounced e x c i t o n - p h o n o n c o u p l i n g may  occur i n the r e g i o n o f the  ( s u r f a c e ? ) and the l i n e b r o a d e n i n g may  r e s u l t t h r o u g h the appearance o f  complicated  i n local lattice vibrations; i n this  c a s e , 32 818  Franck-Condon p r o g r e s s i o n s cm  1  i n f l u o r e s c e n c e and 32 910  cm  1  i n absorption  (measured  as band maxima) may  b o t h connect t h e same e l e c t r o n i c l e v e l s i n the  I t i s t h e n tempting  to speculate f u r t h e r that t h i s perturbed  c o r r e l a t e s w i t h the A u (k=0)  distortion  crystal.  excited level  o r B„ l e v e l o f the b u l k c r y s t a l , w h i l e the B, 3g lu  l i e s at 33 039 cm  above has o v e r - e s t i m a t e d C. Spectra i n a Matrix  level  J  ; i f t h i s i s s o , t h e n the p r e l i m i n a r y c o m p u t a t i o n the f a c t o r group  splitting.  Only o v e r a l l assignments o f the e l e c t r o n i c t r a n s i t i o n s were made i n t h e s t u d y o f the c r y s t a l s p e c t r a .  The  f i n e r v i b r a t i o n a l d e t a i l \\=as  examined  - 120 -  by r e c o r d i n g s p e c t r a o f f l u o r e n e i n a p o l y c r y s t a l l i n e n-heptane where the l i n e w i d t h was 1.  The A b s o r p t i o n  about 5 cm  matrix  ~.  Spectrum  The a b s o r p t i o n spectrum o f f l u o r e n e i n n-heptane shown i n F i g . 23 and a v i b r a t i o n a l a n a l y s i s  a t about 15°K i s  i s g i v e n i n T a b l e 23.  The  108 e l e c t r o n i c o r i g i n formed a " S h p o l s k i i m u l t i p l e t "  w i t h weak components  at 33 107, 33 123, 33 137, 33 160, 33 192, 33 217 and 33 247 c m  -1  as w e l l  as a p r i n c i p a l component a t 33 174 cm *; a l l members o f t h e m u l t i p l e t were a c t i v e i n a b s o r p t i o n and f l u o r e s c e n c e . The e n t r i e s  l i s t e d i n T a b l e 25  represent only those l i n e s a s s o c i a t e d w i t h the p r i n c i p a l o r i g i n . In t h e spectrum o f the f l u o r e n e s u b l i m a t i o n f l a k e , o n l y  fundamentals  and c o m b i n a t i o n s a r e a l l o w e d ; i n d e e d , the c r y s t a l spectrum p r o v i d e d . e s p e c i a l l y s e n s i t i v e method o f l o c a t i n g  intervals.  as  The s e v e r a l B^  fundamentals a c t e d as independent " f a l s e " o r i g i n s w i t h A^ fundamentals upon them h a v i n g n-heptane  about t h e same Franck-Condon  spectrum.  the n-heptane  built  f a c t o r s as shown i n the  I n t h i s way, most o f t h e fundamentals i d e n t i f i e d i n  spectrum were a s s i g n e d A^ symmetry.  Those u n a s s i g n e d may  w e l l be A^ t o o s i n c e t h e y a r e not f a l s e o r i g i n s i n t h e c r y s t a l spectrum. T a b l e 23.  The a b s o r p t i o n spectrum ' t a k e n a t about 15°K crystal  Crystal 33 039  Int.b  of a fluorene  (ab f a c e ) and o f f l u o r e n e i n an n-heptane n-heptane  Int.  33 174  vs  origin  210  s  210,  222  w  222  399  s  399, A  420  w  " 2 x 210  matrix.  Remarks  b  A  2  - 121 -  Crystal  Int.  b  n-heptane 590  601  785  Int. vw  1506  C  607  w  210 + 3 9 9 - 2  683  w  683  725  vs  725, A  :  785, B  2  :  m 834  m  834, A  846  m  846  938  mw  210  952  vw  222 + 7 2 5 + 5  +725+3  977, B  2  :  985  s  985, A  1044  w  210 + 834  1125  mw  399 + 725 + 1  1154  m  1154 785 + 3 9 9 - 5 : 1179, B,  w 1197  1210  590 6C4, B  w  977  1179  Remarks  1  210  +985+2  785_ + 2 x 210 + 5; 1210, B ?  vw  2  1227, A  1227  s  1321  s  1 1321, A,  1383  w  399 + 985  1410  w  1410  1433  vw  210 + 1277 - 4  1457  ms  2 x 725 + 7 ? ; 1457, A 1 785 + 725 - 4  m 1532  1  210 + 1321 + 1? 1532, A  1550  vw  1550, B  1570  vw  1179 + 3 9 9 - 8 1715  mw  2  725 + 985 + 5  1591  WW  1179 + 2 x 210 - 8  1703  w  977  1769  w  785 + 9 8 5 - 1  +725+1  }  - 122 -  Crystal  Int.  1810  vw  D  n-heptane  Int.  977 1818  1901  2095  Remarks  D  +834-1  834 + 985 - 1  WW  1179  w  +725-3  1956  w  725 + 1227 + 4  1978  WW*  2 x 985 + 8  2053  vw  725 + 1321 + 7  vw  785 + 1321 - 11  The p o s i t i o n o f t h e e l e c t r o n i c o r i g i n i s g i v e n i n cm e n t r i e s show d i f f e r e n c e s from the o r i g i n i n cm !.  a l l other  -  R e l a t i v e l i n e s t r e n g t h s i n t h e c r y s t a l and n-heptane s o l u t i o n not be compared.  should  c Intervals  2.  i d e n t i f i e d o n l y from t h e c r y s t a l spectrum a r e u n d e r l i n e d .  The F l u o r e s c e n c e  Spectrum  A microdensitometer  tracing  o f t h e f l u o r e s c e n c e spectrum o f f l u o r e n e  i n n-heptane a t about 15°K i s shown i n F i g . 24 and f r e q u e n c y  differences  o f t h e l i n e s from t h e p r i n c i p a l o r i g i n a r e l i s t e d i n T a b l e 24. p a l o r i g i n a t 33 174 cm  1  i s almost c o m p l e t e l y  reabsorbed i n the fluorescence  spectrum ( t h e mark o f a f a i r l y s t r o n g t r a n s i t i o n ) measured from t h e a b s o r p t i o n spectrum.  The p r i n c i -  and i t was most  readily  The f i r s t s t r o n g l i n e a t 33 159 cm  1  96 was chosen as t h e o r i g i n by Nurmukhametov and Gobov s t u d i e d a t 77°K, and, as a r e s u l t , our f r e q u e n c y variation  when compared w i t h t h e i r v a l u e s .  choice of o r i g i n .  spectrum  d i f f e r e n c e s show a minor  The f i n e r d e t a i l a v a i l a b l e  our l o w - t e m p e r a t u r e spectrum shows t h a t o v e r t o n e s f a c t o r i l y with.our  in their  c o u l d be a s s i g n e d  from  satis-  _ 123 _  A l t h o u g h p o l a r i z e d d a t a were not a v a i l a b l e from the n-heptane spectrum by analogy with' the a b s o r p t i o n spectrum a l l s t r o n g l i n e s a r e e x p e c t e d t o mark t o t a l l y symmetric v i b r a t i o n s .  I n any e v e n t , i n t e r v a l s which must  c o r r e s p o n d t o fundamentals have been i d e n t i f i e d and t h e i r assignment  will  be the s u b j e c t o f c h a p t e r 7.  848,  1019, 1233 and 1615 cm  1  C e r t a i n l y the i n t e r v a l s 213, 413, 746,  r e p r e s e n t A^ fundamentals s i n c e t h e y appear as  overtones.  T a b l e 24.  Energy 33  .  The f l u o r e s c e n c e spectrum o f f l u o r e n e i n n-heptane at  Int.  174  Remarks Origin  (reabsorbed)  213  ms  213,  227  ms  227  413  s .  413, A  w  2 x 213 + 2  626  w  213 + 413  633  w  633  746  vs  746, A  825  w  2 x 413 - 1  848  s  848, A  958  mw  213 + 746 - 1  970  mw  227 + 746 - 3  1019  s  1019, A  1088  w  1088  1125  w-  1125  1158  ms  413 + 746 - 1  1192  m  1192  1206  m  1206  1233  ms  1233,  1285  w  2 x 213 + 848 + 11  428  A  1  A ; 213 + :  1019  ^15°K  - 124 _  Energy  Int.  Remarks  1297  m  1297  1322  m  1322  1349  ni  1349  1384  w  633 + 746  1435  w  413 + 1019 + 3  1446  vw  213 + 1233  1476  ms  1476  1495  m  2 x 746 + 3  1583  w  1583  1598  m  746 + 8 4 8 + 4  1615  s  1615, A  1647  w  413 + 1233 + 1  1696  w  213 + 1476 - 3; 2 x 848  1709  w  227 + 1476 + 6  1767  m  746 + 1019 + 2  1825  w  213 + 1615 - 3  1838  w  227 + 1615 - 4  1868  w  848 + 1019 - 1  1893  vw  413 + 1476 + 4  1904  vw  413 + 2 x 746 + 1  1933  vw  633 + 1297 + 3  1968  mw  213 + 746 + 1019 - 10  1981  mw  746 + 1233 + 2  2029  w  413 + 1615 + .1  2045  w  746 + 1297 + 2;  2078  w  848 + 1233 - 3  2092  w  746 + 1349 - 3  2184  vw  413 + 746 + 1019 + 6  2213  vw  1019 + 1192 + 2  2229  mw  746 + 1476 + 7  2255  V/  1019 + 1233 + 3  2330  w  848 + 1476 + 6  +.5  :  2 x 1019 + 7  _ 125 _  Energy  Int.  Remarks  2345  w  848 + . 2 x 746 + 5  2363  mw  746 + 1615 + 2  2392  w  1158 + 1233 + 1  2456  mw  848 + 1612 - 7; 2 x 1233 - 10  2504  w  1019 + 1476 + 9  2581  w  1233 +• 1349 - 1  2638  w  1019 + 1615 + 4  2721  w  2 x 848 + 1019 + 6  2776  w  413 + 746 + 1615 + 2  2848  w  1233 + 1615  2961  w  1349 + 1615 - 3  3094  w  1476 + 1615 + 3  3228  w  2 x 1615 - 2  3.  The T r i p l e t  State  The phosphorescence o f - f l u o r e n e i n n-heptane a t 20 and 77°K has been s t u d i e d by s e v e r a l a u t h o r s ^  5 1  ^ "*'^. 51  A d e t a i l e d r e p o r t w i l l n o t be made  h e r e j i n s t e a d , some s i g n i f i c a n t p o i n t s a r e enumerated below: (i)  There were at l e a s t f o u r members t o t h e l e a d i n g S h p o l s k i i m u l t i p l e t  w i t h t h e p r i n c i p a l o r i g i n a t 23 798 cm  ( i i ) the high-energy l i n e s i n  the s p e c t r a o f Nurmukhametov and G o b o v ^ and Heckman ''' were caused by 11  an i m p u r i t y ; ( i i i ) because o f d i f f e r e n t a n n e a l i n g  e f f e c t s on t h e sample,  the i n t e n s i t y p a t t e r n amongst t h e l i n e s o f t h e m u l t i p l e t s was n o t r e p r o d u c i b l e f r o m experiment t o experiment so t h a t minor d i f f e r e n c e s between the v a r i o u s r e p o r t s may be expected and ( i v ) a l t h o u g h t h e r e i s a p p a r e n t l y b e t t e r r e s o l u t i o n i n our spectrum a t about 15°K, t h e v i b r a t i o n a l a n a l y s i s was i n s u b s t a n t i a l agreement w i t h t h a t a l r e a d y p r e s e n t e d by T e p l y a k o v and rp  Irusov.  109  - 126  -  A microdensitometer t r a c i n g of the t r i p l e t - t r i p l e t  absorption  spectrum  i n t h e n-heptane m a t r i x i s shown i n F i g . 25 w i t h an a n a l y s i s o f t h e spectrum i n T a b l e 25.  T h i s t r a n s i t i o n has a l r e a d y been observed i n p a r a f f i n s o l v e n t s 112  at room t e m p e r a t u r e , was  113 '  a l t h o u g h under t h e s e c o n d i t i o n s t h e  q u i t e b r o a d and s t r u c t u r e l e s s . The  low-temperature  spectrum  spectrum d i s p l a y e d  c o n s i d e r a b l e v i b r a t i o n a l s t r u c t u r e even though the l i n e w i d t h was 12 cm \  •  about  c o n s i d e r a b l y g r e a t e r t h a n f o r t h e s i n g l e t - s i n g l e t spectrum.  The  l i n e b r o a d e n i n g on warming t h e m a t r i x r e s u l t s from a g r e a t l y enhanced r a t e o f i n t e r n a l c o n v e r s i o n and perhaps from the p r e s e n c e o f "hot bands".  The  i n t e n s i t y p a t t e r n i n t h e v i b r o n i c bands i s q u i t e s i m i l a r t o t h a t i n t h e s i n g l e t a b s o r p t i o n , f l u o r e s c e n c e and phosphorescence  s p e c t r a so t h a t , even  f o r t h e h i g h - e n e r g y s t a t e s i n v o l v e d h e r e , the f l u o r e n e m o l e c u l e has  essentially  r e t a i n e d t h e shape determined by the o-bond framework, y e t w i t h t h e CC bond s t r e n g t h s a p p r e c i a b l y lowered s i n c e t h e r i n g - s t r e t c h i n g modes were e s p e c i a l l y reduced. T a b l e 25.  The t r i p l e t - t r i p l e t  a b s o r p t i o n spectrum o f f l u o r e n e i n  n-heptane a t about  15°K.  Energy  Int.  Remarks  26 530  s  origin  208  m  208  230  m  230  402  m  402  488  w  488  508  w  508  576  w  576  609  ms  609; 208 + 402 - 1  - 127 -  Energy  Int.  Remarks  721  ms  721  819  w  208 + 609  +  2  937  w  208 + 721  +  8  1013  w  402 + 609 + 2  1063  mw  1063  1149  mw  1149  1195  m  1195  1254  w  1254  1302  w  1302  1344  m  1344;  1524  w  1524  3-  208 + 1149  - 13?  I n t e r v a l s a p p e a r i n g w i t h s t r e n g t h g r e a t e r t h a n mw p r o b a b l y A, fundamentals i n t h e upper t r i p l e t s t a t e .  represent  origin  1 2 6  5 0 0  j 2 7  O O O  1  ,  2 7 S O O  2 S O O O  wavenumber ( c m  Fig.  25  The t r i p l e t - t r i p l e t at about 15°K.  - 1  1  :  2 8  5 0 0  )  a b s o r p t i o n spectrum o f f l u o r e n e i n n-heptane  128 The p u r e f l u o r e n e c r y s t a l d i d n o t phosphoresce ( a c t u a l l y , t h e r e was a faint, long-lived,  green e m i s s i o n t o o weak t o r e c o r d w i t h t h e s p e c t r o g r a p h ) .  However, when t h e f l u o r e n e was doped w i t h d i b e n z o t h i o p h e n e phosphorescence was r e c o r d e d a t t h e l o w e s t t e m p e r a t u r e s  an i n t e n s e , b l u e  available.  The  p h o s p h o r e s c e n c e was s t r o n g e r i n b_ t h a n £ p o l a r i z a t i o n w i t h t h e v i b r a t i o n a l s t r u c t u r e e s s e n t i a l l y i d e n t i c a l t o t h a t i n t h e n-heptane m a t r i x ; t h e two s p e c t r a a r e compared i n F i g . 26. c r y s t a l was t e m p e r a t u r e  The e m i s s i o n i n t e n s i t y from t h e doped  dependent ( t h e e m i s s i o n was n o t d e t e c t e d a t about  15°K) s u g g e s t i n g t h a t t h e r a d i a t i o n o c c u r s from s h a l l o w t r a p s . triplet  s t a t e of dibenzothiophene  l i e s about 600 cm  t r i p l e t band o f t h e f l u o r e n e m a t r i x .  1  The l o w e s t  above t h e l o w e s t  I t may be c o n c l u d e d t h a t t h e source  of t h e b l u e phosphorescence i s an i m p u r i t y - i n d u c e d t r a p p i n g l e v e l p r o b a b l y about 30 cm  1  below t h e f l u o r e n e t r i p l e t  band.  I  v  F i g . 26  The phosphorescence o f f l u o r e n e (a) i n t h e c r y s t a l a t about 6°K when induced by t h e a d d i t i o n o f d i b e n z o t h i o p h e n e i m p u r i t y and (b) i n n-heptane a t about 15 K.  - 129 -  A v i b r a t i o n a l a n a l y s i s o f t h e i n d u c e d c r y s t a l phosphorescence i s shown i n T a b l e 26.  The same f u n d a m e n t a l s were found i n o u r n-heptane  solution  s p e c t r a (phosphorescence and f l u o r e s c e n c e ) a l t h o u g h t h e r e were some minor changes b r o u g h t about by s o l v e n t e f f e c t s . frequencies  Some a c t i v e  (local)  lattice  ( 3 0 , 46 and 74 cm •*") were b u i l t on t h e s t r o n g e r v i b r o n i c  lines  b u t t h e s e e n t r i e s have been o m i t t e d from T a b l e 26 i n t h e i n t e r e s t s o f brevity.  The i n t e r v a l s 111 and 136 cm  1  have been i n c l u d e d s i n c e  b o t h may r e p r e s e n t i n t r a m o l e c u l a r f u n d a m e n t a l s ; a 126 cm p r o m i n e n t i n t h e n-hep'aane phosphorescence.  1  one o r  i n t e r v a l was  Low f r e q u e n c y i n t e r v a l s were 68  found i n t h e f l u o r e s c e n c e spectrum o f a n t h r a c e n e - d . ^ i n f l u o r e n e ,  for  example, and t h e s e were l a t e r a t t r i b u t e d t o m a t r i x - i n d u c e d m o l e c u l a r f u n d a 114 mentals.  A  m o l e c u l a r fundamental o f f l u o r e n e has been o b s e r v e d (see  the f o l l o w i n g c h a p t e r ) i n t h e i n f r a r e d c y r s t a l spectrum w i t h f a c t o r - g r o u p components a t l l l f B ^ ) and 126 cm ^ C 2 ) j B  t  n  e  U  components were not found.  Raman-active  factor-group  However, t h e appearance o f t h e s e i n t e r v a l s may  a r i s e from t h e same e f f e c t t h a t produced t h e bands to t h e r e d o f t h e o r i g i n i n t h e a b s o r p t i o n spectrum o f phenanthrene i n f l u o r e n e ; ^ ' ^ ^ t h e same 1  i n t e r v a l s were found i n t h e a b s o r p t i o n spectrum o f c a r b a z o l e i n f l u o r e n e and t h e i r , r e l a t i v e s t r e n g t h s appeared t o be c o n c e n t r a t i o n The prominent i n t e r v a l s i n phosphorescence  dependent.  (also a c t i v e i n fluorescence)  c o r r e s p o n d e d t o A^ f u n d a m e n t a l s and were a l l b u i l t on t h e one o r i g i n - a c h a r a c t e r i s t i c o f an o r b i t a l l y - a l l o w e d t r a n s i t i o n .  This suggestion i s  s u p p o r t e d by t h e e x c e l l e n t agreement between t h e l o w e s t - e n e r g y T <— S 115 a b s o r p t i o n band 26).  and the h i g h e s t - e n e r g y T — * » S e m i s s i o n band (see T a b l e  The measured p o l a r i z a t i o n r a t i o o f phosphorescence  i n the perturbed  c r y s t a l i s c o n s i s t e n t w i t h t h e c o n c l u s i o n ' ^ t h a t most o f t h e e m i s s i o n i s out-of-plane polarized.  However, t h e o r b i t a l  symmetry o f t h e t r i p l e t  state  - 130 -  cannot be d e t e r m i n e d u n t i l t h e p a r t i c u l a r n a t u r e o f t h e s p i n - o r b i t  inter-  a c t i o n i s known.  T a b l e 26.  The phosphorescence  spectrum o f f l u o r e n e  i n a c r y s t a l doped w i t h  d i b e n z o t h i o p h e n e a t about 6°K.  Energy  Int.  Remarks  23 607  vs  origin  111  m  see t e x t  136  m  see t e x t  219  m  219  328  w  111 + 219 - 2  352  vw  136  414  m  414  438  vw  2 x 219  564  W W  564  634  m  634  743  s  743  847  s  847  960  mw  219 + 743 - 2  1021  m  1021  1067  w  219  1095  m  1095  1157  m  414 + 743; 1157?  1193  m  1193  1213  vw  1213  1237  m  1237  1269  • w  +219-3  +847+1  2 x 634 + 1  1297  ms  1297  1379  w  634  1411  vw  219 + 1193 + 1  1479  s  1479; 634 + 8 4 7 - 2  1577  m  1577  +743+2  -  Energy  131 -  Int.  Remarks  1612  vs  1612  1696  m  2 x 847 + 2  1722  m  111 + 1612 + 4  1752  mw  136 + 1612 + 4  1830  m  219 + 1612 - 1  1894  w  414 + 1479 + 1  1934  w  743 + 1193 - 2  1975  vw  743 + 1237 - 5  2001  vw  414 + 743 + 847  2037  mw  743 + 1297 - 3  2114  vw  634 + 1479 + 1  2145  vw  847 + 1297 + 1  2224  w  743 + 1479 + 2  2249  mw  634 + 1612 + 3  2323  w  847 + 1479 - 3  2554  ms  743 + 1612 - 1  2453  ms  847 + 1612 - 6  2572  vw  1095 + 1479 - 2  2595  vw  2 x 1297 + 1  2631  vw  1021 + 1 6 1 2  2702  w  1095 + 1612 - 5  2765  w  414 + 743 + 1612  2799  w  1193 + 1612 - 6  2848  w  1237 + 1612 - 1  2898  w  1297 + 1612 - 11  3090  w  1497 + 1612 - 1  3222  mw  2 x 1612 - 2  - 2  1  Chapter 7 A V i b r a t i o n a l Assignment o f F l u o r e n e from t h e I n f r a r e d and Raman S p e c t r a  A.  Introduction 117 In a recent paper,  the polarized infrared spectra of a fluorene  s u b l i m a t i o n f l a k e have been r e p o r t e d and a v i b r a t i o n a l a n a l y s i s deduced by comparing l i n e i n t e n s i t i e s w i t h t h o s e o f a powder spectrum and by measuri n g l i n e - s h a p e s i n t h e vapour spectrum. A^ an  modes  were d i s t i n g u i s h e d  by t h e d i f f e r e n t p o l a r i z a t i o n r a t i o s i n t h e ab s p e c t r a , and  modes were  e n t i r e l y absent i n t h e ab s p e c t r a b u t appeared i n t h e spectrum o f t h e p o l y crystalline material.  I n t h i s work t h e v i b r a t i o n a l a n a l y s i s i s extended  by r e c o r d i n g t h e i n f r a r e d s p e c t r a o f a s i n g l e c r y s t a l low energy r e g i o n from 50 t o 400 cm  (including the very  with the plane of p o l a r i z a t i o n  o f t h e i n c i d e n t l i g h t a l o n g a l l t h r e e c r y s t a l a x e s , and by making as complete a s t u d y o f t h e Raman spectrum as p o s s i b l e .  The c r i t e r i a used i n t h e  i n t e r p r e t a t i o n o f t h e fundamental v i b r a t i o n s have a l r e a d y been d i s c u s s e d i n chapter 3 which deals w i t h the v i b r a t i o n s o f c a r b a z o l e . B.  S e l e c t i o n Rules The r e l a t i o n s h i p between t h e m o l e c u l a r and c r y s t a l axes i s i l l u s t r a t e d  i n F i g . 6, and t h e s e l e c t i o n r u l e s f o r t h e f r e e m o l e c u l e and f o r the u n i t Note t h a t t h e m o l e c u l a r a x i s c o n v e n t i o n used i n r e f e r e n c e 117 has been changed t o conform w i t h t h e i n t e r n a t i o n a l l y recommended one§0 used h e r e ; t h i s i n v o l v e s t h e i n t e r c h a n g e o f t h e symbols B, and B„.  - 133 -  c e l l modes a r e c o r r e l a t e d  i n T a b l e 27.  F o r t h e wavevector k. = 0, t h e f o u r  molecules i n the u n i t c e l l give r i s e t o four u n i t c e l l v i b r a t i o n s transform l i k e the i r r e d u c i b l e representations one o f t h e u n i t c e l l v i b r a t i o n s d e r i v e d  of the  from t h e  which  f a c t o r group.  f r e e m o l e c u l e modes i s  i n f r a r e d a c t i v e , and i t s t r a n s i t i o n d i p o l e i s p a r a l l e l t o t h e c a x i s . t h e case o f  Only  In  o r B^ f r e e m o l e c u l e s v i b r a t i o n s , two o f t h e c r y s t a l s t a t e s  are i n f r a r e d a c t i v e and two a r e Raman a c t i v e .  T a b l e 27.  C o r r e l a t i o n t a b l e showing t h e s e l e c t i o n r u l e s f o r t h e i s o l a t e d m o l e c u l e and f o r t h e c r y s t a l o f f l u o r e n e  M o l e c u l a r Group Bases  C 2v> C  Species  xx,yy,zz;  z  Species  Species  xz;  x  B  ab  *g 2u  b  B, 3u  a —  l  D  aa,bb,cc  .g A'  < 2h> Bases  A  l  A  F a c t o r Group  S i t e Group (C )  A u  - 134 C.  -  Infrared Spectra P o l a r i z e d s p e c t r a were r e c o r d e d  w i t h l i g h t i n c i d e n t on t h e ab_, bc_ and  ac f a c e s o f a s i n g l e c r y s t a l o f f l u o r e n e and a s e t o f independent s p e c t r a are shown i n F i g s . 28-30. was  To the e x t e n t t h a t our s i n g l e - c r y s t a l s e c t i o n  somewhat t h i c k e r t h a n W i t t ' s o r i e n t e d , m u l t i r- c r y s t a l l i n e sample, our  ab s p e c t r a f o r the h i g h e r - e n e r g y  r e g i o n (shown i n F i g . 3 0 ) c o n f i r m h i s  117 results  and supplement them s i n c e the weaker l i n e s have become more  prominent. 28) where  There was  one d i f f e r e n c e i n t h e low-energy s p e c t r a (see F i g .  the s p l i t l i n e c e n t e r e d a t 260 cm  a_ t h a n b_ p o l a r i z a t i o n . may  1  i s s l i g h t l y more i n t e n s e i n 117  This i s a r e v e r s a l of Witt's o b s e r v a t i o n  and  be a t t r i b u t e d t o the f a c t t h a t the l i n e f e l l a t the l i m i t o f h i s  spectrometer.  There was  some d i f f i c u l t y i n d i s t i n g u i s h i n g l a t t i c e modes  from l o w - f r e q u e n c y m o l e c u l a r  f u n d a m e n t a l s , so the spectrum o f f l u o r e n e  i n a c y c l o h e x a n e s o l u t i o n , measured from 50 t o 600  cm \  i s shown i n F i g . 27  t h e s o l u t i o n spectrum at h i g h e r e n e r g i e s has been r e p o r t e d by W i t t .  100  F i g . 27  The  200  300  400  500  600  cm"  1  i n f r a r e d spectrum o f f l u o r e n e i n a c y c l o h e x a n e s o l u t i o n i n  the l o w - f r e q u e n c y r e g i o n ; t h e b r o k e n c u r v e r e p r e s e n t s the spectrum in a dilute  solution.  600 cm-'  F i g . 28  The p o l a r i z e d i n f r a r e d s p e c t r a o f f l u o r e n e s i n g l e c r y s t a l a t low _ frequencies. The ab s e c t i o n was 1 mm t h i c k f o r t h e range 50-160 cm and 0.1 mm t h i c k f o r 160-650 cm" , and t h e ac s e c t i o n was. 0.79 mm t h i c k , f o r tlie range 5Q-16Q cm-1 and Q.15 mm f o r 160-65Q c m ~ l .  l  1  3200  Wavenumber ( c m ) -1  Fig  29' 'The' i n f r a r e d s p e c t r a - i n t h e CH s t r e t c h i n g r e g i o n : (a) an ab c r y s t a l s e c t i o n , (b) a be c r y s t a l s e c t i o n , and (c) i n a carbon t e t r a c h l o r i d e section.  - 137  Table  29 l i s t s t h e observed  ments made on t h e assumption are s m a l l .  -  f r e q u e n c i e s o f t h e bands and t h e i r a s s i g n -  t h a t d e v i a t i o n s from an o r i e n t e d - g a s model  In t h i s approximation, the r e l a t i v e l i n e strengths along t h e  c r y s t a l axes a r e g i v e n as t h e squares o f t h e d i r e c t i o n axes on t h e c r y s t a l axes (see T a b l e  cosines of molecular  28) when, q u a l i t a t i v e l y ,  modes a r e  expected t o be most i n t e n s e a l o n g b, B a l o n g a, and B a l o n g c_. 1 • ^ Table  28. The r e l a t i v e band i n t e n s i t i e s o f f l u o r e n e a l o n g t h e c r y s t a l axes c a l c u l a t e d i n t h e o r i e n t e d - g a s  A  Table  B  l  B  2  a  0,.326  0..674  0.000  b  0..674  0..326  0.000  c  0,.000  0,.000  1.000  29. The i n f r a r e d  Solution  l  approximation.  spectrum  //a_  of fluorene  //b_  //c  46 vw 70 ms 80 m  101 vw 111 s  126 ms 130 vw  ; 150 vvw  b_ 3u b„ 3u b 2u b„ 2u b, lu n  100 w 120 m  Symmetry  b. lu see t e x t  215 mw  216 vw  218 mw  A  247 v s  255 vs  265 vs  B  410 s  410 ms  408 m  see t e x t  x  5  -  Solution 467  m  487  mw  //a 476  621  m  627  693  mw  694  138 -  //£  //b w  471  m  see 487  m  B  2  542  m  B  2  618  ms  B  2  w  629  m  A  l  s  692  m  B  l  B  2  B  l  722 737  vs  735  vs  841  w  854  ms  859  w  873  910 951  s  1001  m  1019  vw  1026  w  1089  1124  w  949  s  ms  904  mw  910  w  ms  2  B  l l  B  2  B  l  B  2  B  l  952  s  975  vw  A  l  990  vw  A  l  B 1  1016  vs  B  ms  1056  vw  1089  s  w  1143  vw  vs  2 l  A  1023  1089  vw  vw  mw  B  A  994 1016  w  ms 865  873  l  A  773  •  w  w  vs 738  851  Symmetry  _2 B  A  l  A  l  1103  s  B  2  1120  w  B  2  1137  vw  B  2 l  A  1147  w  1152  s  1154  vw  1185  m  1188  s  1184  s  1194  sh  1188  vs  1213  mw  1215  m  B  l  A  l  B  2 2  1  text  _ 139 -  Solution 1230 w  1231  m  Symmetry -  //c  //b  //a  1231  m  1291  w  3  1295 ra  1294 s  1311  1303  m 1319 w  1331  1319 w  w  1377 vw  1340 w  1340 vw  1380 w  1380 w  1399 s  1397 vs  1410 w  1406 m  vs  1392 vs  2 see B  1336 s  l  A  1382 w  B  1446 s  1426 w  1440 vs  1440 vs 1440 s  1477 s  1471  s  1521  m  1575 w  1570 w  l  1417 w  1450 s  1486 vw  2  see B  1426 w  1486 vw  1570 m 1582 vw  1592 mw  1592 mw 1602 vw 1635 w  1643  w  '2902 m  2907 mw  2927 m  2920 w  1643  3016 mw  ms  3020 s 3028 sh 3040 s  3045 m  3048 ms 3048 m  2• 2  w  3006 m 3023 m  B  FL  2921  3062 s  text  text  -  Solution 3070  -  //b  //a  s  140  3063  m  3064  s  3072  sh  3072  sh  3094  vw  V sh  B  ms 3153  a  3-  l  A  3084 3096  Symmetry  /'/£_  m  L a t t i c e modes are d e s i jj n a t e d u s i n g l o w e r - c a s e symbols t o them from m o l e c u l a r v i b r a t i o n s  2  A  l  B  2  distinguish  D. Raman S p e c t r a The Raman s p e c t r a o f f l u o r e n e as a s o l u t i o n , , a 119  powder  melt ^ 1  2  and a  120  '  have been used t o make a t e n t a t i v e  fundamentals;  i d e n t i f i c a t i o n o f a few  however, no p o l a r i z a t i o n d a t a have been a v a i l a b l e .  s p e c t r a o f a s i n g l e c r y s t a l and d e p o l a r i z a t i o n f o r a carbon t e t r a c h l o r i d e  solution  3 2 ) a r e r e p o r t e d here f o r t h e f i r s t  Polarized  r a t i o s o f t h e l i n e s measured  (see Tables 3 0 and 3 1 , and F i g s . 3 1 and time.  The assignment o f the t o r s i o n a l l a t t i c e modes g i v e n i n T a b l e 3 0 was made using the s e l e c t i o n r u l e s  l i s t e d i n T a b l e 2 7 . The i n t e n s i t i e s o f t h e l i n e s  c o r r e s p o n d i n g t o i n t r a m o l e c u l a r v i b r a t i o n s may be e s t i m a t e d f o r t h e o r i e i i t e d - g a s model by t r a n s f o r m i n g t h e components o f t h e p o l a r i z a b i l i t y t e n s o r from t h e m o l e c u l a r frame Q c , y_, z) t o t h e c r y s t a l frame ( a , b_, c j . In t h i s a p p r o x i m a t i o n , t h e  i n t e n s i t y o f a lone i n the c r y s t a l s p e c t r a i s  r e l a t e d t o . 4i5t4 s f r e e - m o l. 1e 0c 6u l e . i8 n8 t0 e n s i t y by t h e e q u a t i o n s : aa xx I .106 .454 .880 .674 bb and .326 1.000 ac cc zz ab.  .220  .220  .121  L bc :  L?"xz.  .326 .674  I  xy I L yzJ  -.141  wavenumber (cm ) -1  F i g . 31  The Raman s p e c t r a o f a f l u o r e n e s i n g l e c r y s t a l . i s d e f i n e d i n T a b l e 32.  The nomenclature  A l l s p e c t r a were r e c o r d e d under  identical  c o n d i t i o n s except t h a t t h e i n t e n s i t y o f t h e (cc) spectrum has been reduced h e r e by a f a c t o r o f t e n .  The l i n e s a t 221, 1480 and 1612 cm  1  e v i d e n t l y appear o n l y t h r o u g h t h e  effectiveness o f the operator a yy  The s p e c t r a i n F i g . 31 were measured under c o n d i t i o n s t h a t were as n e a r l y t h e same as p o s s i b l e .  However, i t would appear t h a t , i f t h e assumption  o f n e g l i g i b l e i n t e r m o l e c u l a r i n t e r a c t i o n i s t o be r e l i e d upon, t h e i n t e n s i t y o f t h e (ab) spectrum s h o u l d be a p p r e c i a b l y i n c r e a s e d b e f o r e any comparison between t h e s p e c t r a i s made s i n c e t h e 743 and 1022 cm  1  i n t e r v a l s may be  '. .7142 '  (ac)  i  1  1  -2GO  *  O  1  1 2CO  1  1  1  1  4 0 0  GOO  1  1  1  8 C O  1  IOOO  1  1  I2CO  i  i  1  I4CO  1600  wavenumber (cm"')  F i g . 32 The Raman s p e c t r a modes.  taken t o represent  o f a fluorene  s i n g l e c r y s t a l showing t h e A^ and  The n o m e n c l a t u r e i s d e f i n e d  i n T a b l e 32.  modes from t h e i r low d e p o l a r i z a t i o n  ratios i n  solution. The  l i n e s a t S46 and 854 cm  1  mark t h e p r e s e n c e o f two m o l e c u l a r  f u n d a m e n t a l s s i n c e t h e y b o t h have A (bb)  spectrum.  The r e g i o n  1400 cm  1  a l s o c o m p l i c a t e d and was i n t e r p r e t e d i n t h e (aa) and (bb) s p e c t r a the  1400 cm  1  interval B  f a c t o r group components i n t h e t o t h e r e d o f t h e e x c i t i n g l i n e was as f o l l o w s :  represented the A  The 1408 cm  1  interval  f a c t o r group component and  component o f a s i n g l e A  1  molecular v i b r a t i o n .  143 T a b l e 30. The Raman spectrum o f f l u o r e n e near t h e e x c i t i n g  b(aa)c  a(bb)c  a(ba)c  a(ca)c  b(cb)c  line.  Symmetry  24  3g  31  b  ig  38 44  '\  66  "lg 77  b  \  88 r  88  3g  a  89  g  The column headings i n d i c a t e , from l e f t t o r i g h t i n s i d e t h e p a r e n t h e s e s , the p o l a r i z a t i o n o f t h e i n c i d e n t and s c a t t e r e d l i g h t and, from l e f t to r i g h t o u t s i d e the parentheses, the p r o p a g a t i o n ' d i r e c t i o n s o f the i n c i d e n t and s c a t t e r e d l i g h t , r e s p e c t i v e l y . No (cc) Raman s c a t t e r i n g was d e t e c t e d .  The l i n e s a t 846 and 854 cm fundamentals spectrum.  1  mark t h e p r e s e n c e o f two m o l e c u l a r  s i n c e t h e y b o t h have A  The r e g i o n 1400 cm  1  f a c t o r group components i n t h e (bb)  t o t h e r e d o f t h e e x c i t i n g l i n e was a l s o  c o m p l i c a t e d and was i n t e r p r e t e d as f o l l o w s : (aa) and (bb) s p e c t r a r e p r e s e n t e d t h e A 1400 cm  i n t e r v a l the  The 1408 cm  interval i n the  f a c t o r group component and t h e  component o f t h e s i n g l e A^ m o l e c u l a r v i b r a t i o n .  The e n t r y i n T a b l e 31 i s t h e mean o f t h e s e v a l u e s . i /  1  - 144 -  T a b l e 31. The Raman spectrum o f f l u o r e n e  CC1.  jy  Crystal  a  Symmetry  221  l  A  258  V  280 mw  /v>. 8  285  A  2  416 mw  .14  421  A  l  546 w  <v-.8 .12  745 s  546  B  2  743  A  787  l  A  2  A  l  846 ms  .21  846  853?vw  ?  854  B  l  1023 s  .10  1022  A  1093 vw  .6  1093  l  A  l  1146 1157 mw  1192  ru  i\J  .5  .6  B  2  1172  B  2  1193  B  2  1156  1195  w  A  l f B l  1213?  A  l  1235 s  .21  1238  A  .21  l  1301 ms  1296  A  l  1301  A  l  1328 mw  .34  1329  A  1351 mw  .34  1349  l  A  .13  1404  l  1405 vw  A  1450  l  1453 vw  ?  A  l  1483 ms  .38  1480  A  1582 w  .8  1578  l  A  1615 v s  .52  1612  l  A  l  A  l  2908 2923 3005? 3020?  W ?  ?  -  145 -  Symmetry  Crystal  CC1. 4 3054  < -5  3050  A  l  3069  <.5  3064  A  l  3089? 3151? 3220?  ci  The d e p o l a r i z a t i o n r a t i o , jo , i s 0.75 f o r n o n - t o t a l l y symmetric v i b r a t i o n s and f a l l s i n the range 0-0.75 f o r symmetric v i b r a t i o n s . The e r r o r s i n the v a l u e s l i s t e d depend on t h e l i n e s t r e n g t h s .  E.  Assignment of Fundamentals  1."  The  Low-Energy R e g i o n .  L a t t i c e modes are expected t o appear i n the  low-frequency  a c c o r d i n g t o s e l e c t i o n r u l e s o u t l i n e d i n T a b l e 27.  The  f r e q u e n c i e s w i t h k_ = 0 f o r the case o f f o u r f l u o r e n e c e l l are d i s t r i b u t e d as f o l l o w s : b, , b„ , and lu 2u'  b_ and 3u  two  number o f  lattice  molecules i n a u n i t  i n each of the symmetry  t h r e e i n each o f the s p e c i e s  spectra  species  a , a. , b, . b g u lg 2g  r  and  V The  t o r s i o n a l l a t t i c e modes t h a t were observed i n the Raman spectrum  have been a s s i g n e d i n T a b l e 30.  The  two  a-polarized  i n the i n f r a r e d spectrum were a s s i g n e d as ^>^ , u  and  100  b^  modes.  u  126  cm  cm  1  1  as ^2 '  anc  U  The  * ^ t  ie  a-polarized  w e a  ^  c-polarized  l i n e a t 111  cm  l i n e s at 101 1  and  w h i c h appeared i n the s o l u t i o n spectrum a t 120  a t 70  the b - p o l a r i z e d  (b_ ) and ou  88 cm  1  u  and  cm  1  .  70 cm  l i n e s at  130  the b - p o l a r i z e d  were t a k e n as f a c t o r group components of a  l i n e i n a - p o l a r i z a t i o n i s probably a b^  l i n e s at 46 and  cm  1  1  80 as  l i n e at  m o l e c u l a r fundamental The  v e r y weak 150  c o m b i n a t i o n of the  cm  l a t t i c e modes  (a ) , a l t h o u g h a b e t t e r energy f i t may g  be  found.for  1  - 146 -  t h i s combination  when t h e m i s s i n g g modes a r e i d e n t i f i e d .  I t i s i n t e r e s t i n g t o -compare t h e l a t t i c e modes observed i n f l u o r e n e 58 with those f o r c a r b a z o l e , s i n c e the carbazole c r y s t a l  b e l o n g s t o t h e same  space group as f l u o r e n e and has i t s f o u r m o l e c u l e s d i s p o s e d i n almost i d e n t i c a l f a s h i o n .  However, i t s h o u l d be noted t h a t t h e axes b_  and c o f t h e c a r b a z o l e c r y s t a l s h o u l d be i n t e r c h a n g e d i s made.  i n the unit c e l l  b e f o r e t h e comparison  I n g e n e r a l , t h e r e i s an i n c r e a s e i n l a t t i c e - m o d e frequency  between  f l u o r e n e and c a r b a z o l e , and , i n p a r t i c u l a r , t h e f a i r l y prominent Raman l i n e s a t 66, 77, 88 and 89 cm  1  i n f l u o r e n e have c o u n t e r p a r t s  c a r b a z o l e spectrum t h a t a r e somewhat g r e a t e r t h a n 100 cm . 1  that the relevant f o r c e constants  i n the This implies  must be g r e a t e r i n c a r b a z o l e , a r e s u l t  which i s i n harmony w i t h ( i ) t h e v e r y much h i g h e r m e l t i n g - p o i n t o f c a r b a z o l e , °3 and ( i i ) t h e o b s e r v a t i o n t h a t c a r b a z o l e has t h e s m a l l e r u n i t c e l l (853 A i n °3 c a r b a z o l e and 921 A 2.  i n fluorene).  A^ Symmetry (22 fundamentals) Prominent b - p o l a r i z e d l i n e s were observed i n t h e i n f r a r e d spectrum a t  217,  628, 857, 1016, 1089, 1186, 1231, 1291, 1319, 1440, 1570 and about  1592  cm  1  and were a s s i g n e d as A^ fundamentals.  The f a i r l y i n t e n s e  intervals  221, 421, 743, 846, 1022, 1238, 1296, 1329, 1349, 1480, 1578 and 1612 cm"  1  i n t h e Raman spectrum, which e i t h e r had a low d e p o l a r i z a t i o n r a t i o o r appeared i n t h e ( c c ) spectrum, were a l s o taken t o r e p r e s e n t A^ fundamentals. There a r e 16 d i f f e r e n t e n t r i e s i n t h e s e combined l i s t s , many o f them common w i t h i n the l i m i t s of experimental of a probable  accuracy  f a c t o r group s p l i t t i n g .  range below 2000 cm  1  probably  of s t r o n g i n f r a r e d a b s o r p t i o n .  (about 5 cm  1  f o r each e n t r y ) and  The m i s s i n g fundamental i n t h e  l i e s a t 1397 cm , which i s c e r t a i n l y a r e g i o n 1  Witt  1 1  ^ has shown t h a t t h e band c o n t o u r i n  - 147 the  vapour spectrum i s c o n s i s t e n t w i t h an  a s s i g n m e n t , and the Raman  d e p o l a r i z a t i o n r a t i o , i n a c a r e f u l remeasurement, the  was  0.13.  However, i n  i n f r a r e d spectrum o f t h e c r y s t a l , i t s i n t e n s i t y i s g r e a t e r i n a_ r a t h e r 117  t h a n b p o l a r i z a t i o n , a r e s u l t found b o t h by W i t t the  same s o r t o f d i s t u r b a n c e seems t o have a f f e c t e d the 1340 cm  line. are  T h i s seems t o be one c l e a r example where i n t e r m o l e c u l a r  s u f f i c i e n t l y s e v e r e t o r e v e r s e an o r i e n t e d - g a s p r e d i c t i o n .  example o c c u r s near 400 cm .  t h a t t h e r e i s an A^ fundamental a t 421 cm  w h i l e the i n f r a r e d  i n d i c a t e s t h a t a B^ fundamental l i e s at 409 cm -1 474 cm  .  1  infrared  interactions Another  Both the Raman and f l u o r e s c e n c e spectrum show  1  at  and i n t h e p r e s e n t work;  1  spectra  w i t h the A^ fundamental 117  Indeed, t h e i n f r a r e d assignment i s the one p r e s e n t e d by W i t t  I t i s not n e c e s s a r y t o suppose t h a t t h e i n t e r a c t i o n s i n t h e c r y s t a l a r e so extreme as t o cause a b r o a d e n i n g o f the A^ m o l e c u l a r s t a t e t o c o v e r t h e range 408-476 cm ; r a t h e r i t i s s u f f i c i e n t t o suppose t h a t the c r y s t a l bands 1  a r i s i n g from t h e 421  (A^) and 474  ( p r o b a b l y not more t h a n 10 cm the  1  (B^) m o l e c u l a r s t a t e s remain narrow  wide) y e t mix s t r o n g l y under the a c t i o n o f  c r y s t a l environment. The 5 CH s t r e t c h i n g fundamentals o f A^ symmetry were o b s e r v e d i n the  i n f r a r e d spectrum at 2920, 3018, 3064, and 3094 cm . 1  the  h i g h e r - f r e o ^ e n c y r e g i o n c o n t a i n a g r e a t e r u n c e r t a i n t y , s i n c e the weaker  l i n e s may  r e p r e s e n t c o m b i n a t i o n s and t h e s t r o n g r e g i o n s o f a b s o r p t i o n an 117  approach t o a c c i d e n t a l degeneracy.  Witt  has a s s i g n e d the symmetry  s t r e t c h i n g v i b r a t i o n o f t h e CH^ group at 2905 cm s t r e t c h a t 2920 cm 3.  The assignments i n  1  1  w i t h the asymmetric  (B^)  on the b a s i s o f t h e band c o n t o u r s o f t h e vapour spectrum.  B^ Symmetry (11 f u n d a m e n t a l s ) E i g h t B^ fundamentals are i d e n t i f i e d i n the p o l a r i z e d i n f r a r e d spectrum  -  148  -  at 119, 260, 693, 735, 910, 951, 1153 and 2905 cm" , 1  a l t h o u g h , as noted  117 above, the r e s u l t from the vapour spectrum t o be m o d i f i e d .  Two  may  cause t h e l a s t  assignment  o f t h e r e m a i n i n g t h r e e fundamentals may be seen as  weak l i n e s at 841 and 873 cm the previous s e c t i o n .  1  and the l a s t i s a t 474 cm  1  as i n d i c a t e d i n  S i n c e some o f t h e s e o u t - o f - p l a n e modes show an  a p p r e c i a b l e s p l i t t i n g , o n l y t h e mean v a l u e s a r e g i v e n above.  The  modes  are not prominent i n the Raman spectrum so t h a t l i t t l e c o r r o b o r a t i o n o f t h e s e assignments i s a v a i l a b l e from t h i s s o u r c e . 4.  A  2  Symmetry (10 f u n d a m e n t a l s )  O n l y two  fundamentals were l o c a t e d from t h e Raman s p e c t r a a t 285  and 787 cm ; no o t h e r r e l e v a n t i n f o r m a t i o n i s a v a i l a b l e . 1  5.  &  2  Symmetry (20 fundamentals)  Of t h e 16 B  fundamentals expected below 2000 cm , 13 o f t h e s t r o n g e s t 1  2  l i n e s i n the £-polarized spectrum a t 487, 542, 618, 994, 1023, 1103, 1215, 1303, 1336, 1440, 1471 and 1521 cm"  1  are assigned to t h i s  No c o m b i n a t i o n c o u l d be found f o r the 487 cm  1  1188,  species.  l i n e a l t h o u g h , t o be  certain  t h a t t h e r e i s none, more complete knowledge o f t h e l o w - f r e q u e n c y A^ fundamentals i s r e q u i r e d . of  The assignment o f the o t h e r l o w - f r e q u e n c y l i n e  o n l y moderate s t r e n g t h as a fundamental i s c o n f i r m e d -by the Raman d a t a .  The Raman s p e c t r a a l s o suggest t h e p r e s e n c e o f B 1193 cm  1  w h i c h may  ?  fundamentals at 1146  and  c o r r e l a t e w i t h the i n f r a r e d bands at 1137 and 1188 cm  The weak l i n e s a t 722 and 904 cm  1  1  .  a r e f a i r l y w e l l i s o l a t e d from o t h e r s t r o n  l i n e s and a r e t a k e n t o mark the p r e s e n c e o f t h e l a s t two f u n d a m e n t a l s . The l i n e a t 1120 cm  1  was not s e l e c t e d as a fundamental s i n c e i t was  not  p r e s e n t i n t h e s o l u t i o n spectrum and was thought t o r e p r e s e n t a c o m b i n a t i o n band d e r i v i n g i t s i n t e n s i t y i n the c r y s t a l from t h e s t r o n g l i n e at 1103 cm  1  - 149 -  The f o u r CH s t r e t c h i n g fundamentals were chosen on t h e b a s i s o f l i n e s t r e n g t h a t 3040 and 3062 cm" , 1  F.  and p o s s i b l y 3006 and 3084  cm" . 1  Discussion The assignments made i n t h e p r e v i o u s  s e c t i o n a r e l i s t e d i n T a b l e 32 where 117  a comparison w i t h W i t t ' s e a r l i e r assignment  T a b l e 32.  Species  i s given.  The assignments o f t h e fundamental v i b r a t i o n s o f f l u o r e n e  Present  Work  217  Ref.  1  Species  Present  Work  Ref. 1  262  421  a  628 743  a  857  472  487  414?  633  542  490  1  618  624  738?*  722?  ?  860  904?  ?  1016  1022 •  1089  1092 1  1186  994  1 000  1023  1025  1103  1109  1231  1190  1146  1291  1234  1188  1160  1319?  1324  1215  1198?  1349  1343  1303  1300  1397  1400  1336  1311  1440  1451 1478  1440 1480  1448  1471  1570  1576  1521  1612  a  1610?  a  1156  J  2920?  2905  3006?  3003?  3018  3019?  3040  3041  3048  3027?  3062  3062  -  Species  A  P r e s e n t Work  150 -  Ref. 1  3064  3047?  3094?  3071?  Species  P r e s e n t Work 3084?  3093?  119  ?  B,  0  2  1  287  Ref. 1  788  260  212?  473  41l  693  545?  735  698  841  740  873  842?  910  1  951  914  1153  954  2905?  2920  a  a  Data t a k e n from t h e Raman spectrum; a l l o t h e r e n t r i e s a r e from t h e i n f r a r e d spectrum.  A p a r t from d i f f e r e n c e s t h a t have a l r e a d y been mentioned, a comparison w i t h W i t t ' s assignment y i e l d s t h e f o l l o w i n g o b s e r v a t i o n s .  (i)I f , in  t h e A^ symmetry b l o c k , W i t t ' s two q u e r i e s a r e l i f t e d out and t h e p r o m i n e n t Raman l i n e s a t 1296 and 1480 cm ment i s r e a c h e d .  1  a r e i n s e r t e d i n t h e i r p l a c e , good agree-  ( i i ) W i t t ' s assignment o f t h e  fundamentals i s  r e m a r k a b l y a c c u r a t e c o n s i d e r i n g t h a t he d i d not have a v a i l a b l e t h e l e s s crowded c _ - p o l a r i z e d spectrum where o n l y  modes appear.  o c c u r i n the complex r e g i o n s around 1150 and 1300 cm . 1  Minor discrepancies More i m p o r t a n t  d i f f e r e n c e s o c c u r a t l o w - f r e q u e n c i e s : we f i n d no e v i d e n c e f o r a B^ fundamental a t 414 cm , y e t have such e v i d e n c e (both i n t h e i n f r a r e d and Raman 1  spectrum) f o r one a t 542 cm . 1  ( i i ) The B  symmetry b l o c k comes i n t o good  -  15.1 -  agreement once i t i s r e c o g n i z e d t h a t t h e Raman l i n e a t 546 cm  1  has, i n f a c t ,  symmetry and t h a t t h e o r d e r i n g i n energy may be r e a r r a n g e d . A c o m p a r i s o n w i t h t h e c a r b a z o l e assignment i s a l s o r e w a r d i n g (see Appendix I I ) .  I n A^ symmetry two p o i n t s a r i s e .  p r o m i n e n t 1327 cm  1  l i n e was t a k e n t o r e p r e s e n t an A^ c o m b i n a t i o n w i t h a  more p r o m i n e n t l i n e a t 910 cm  1  b e i n g a c c e p t e d as t h e f u n d a m e n t a l ; i n  f l u o r e n e , t h e l i n e c o r r e s p o n d i n g t o 910 cm has been r e v e r s e d .  In carbazole the f a i r l y  1  i s m i s s i n g and t h e assignment  I t i s not p o s s i b l e t o make a s a t i s f a c t o r y c h o i c e between  t h e s e a l t e r n a t i v e t y p e s o f assignment on t h e b a s i s o f t h e d a t a p r e s e n t l y available. at 1397 cm  The second p o i n t a r i s e s from t h e absence o f an A^ fundamental 1  i n t h e c a r b a z o l e spectrum; thus t h e normal c o o r d i n a t e may be  p r i m a r i l y r e p r e s e n t e d by t h e CH^ s c i s s o r i n g m o t i o n .  T h i s argument i s  121 r e i n f o r c e d by d e u t e r a t i o n e f f e c t s .  U s i n g s i m i l a r arguments, i t may be  deduced t h a t t h e normal c o o r d i n a t e f o r t h e 693 cm  1  B^ fundamental i s made  up l a r g e l y o f t h e o u t - o f - p l a n e r o c k i n g m o t i o n o f t h e CH^ group. In view o f t h e assignment o f t h e A^ and B^ fundamentals from i n f r a r e d and Raman d a t a , a somewhat n o v e l i n t e r p r e t a t i o n ' o f the medium s t r e n g t h 227 cm  1  i n t e r v a l which appears i n b o t h t h e f l u o r e s c e n c e and phosphorescence  spectrum i s p o s s i b l e .  The a n a l y s i s o f t h e f l u o r e s c e n c e and phosphorescence  shows t h a t t h e prominent v i b r a t i o n s a r e e i t h e r o f A^ o r B^ symmetry w i t h t h e g r e a t e s t i n t e n s i t y r e s i d i n g i n t h e A^ modes.  The 227 cm  1  does n o t r e p r e s e n t  a fundamental o f e i t h e r t h e A. o r B„ s p e c i e s , and t h e r e f o r e must be t h e 1 z o v e r t o n e o f t h e B^ fundamental a t 119 cm  1  i n the fluorene c r y s t a l .  The  o v e r t o n e i s symmetry a l l o w e d s i n c e i t b e l o n g s t o t h e t o t a l l y symmetric r e p r e s e a t i o n o f t h e C,, m o l e c u l a r p o i n t group; thus t h e problem r e m a i n i n g i s t o account f o r i t s i n t e n s i t y .  I n t h e harmonic a p p r o x i m a t i o n , t h e r a t i o o f t h e  i n t e n s i t y o f t h e f i r s t o v e r t o n e t o t h a t o f t h e o r i g i n band i s g i v e n by t h e  - 152 -  square o f t h e r a t i o s o f t h e o v e r l a p o f two harmonic  ^ , 0 _ R ( 2 , 0 ) ,2 . 00 )l I RR(f0n , r  LL  0  j  ,  JJ  0  =  oscillators  122  1 v ' - v"-,2 22 vv'' ++ vv" r  LL  n  J  n 1  J  where v' and v " a r e r e s p e c t i v e l y t h e ground and e x c i t e d s t a t e f r e q u e n c i e s o f a p a r t i c u l a r normal mode.  E q u a t i o n (7.1) i s v a l i d i f t h e o r i g i n o f  t h e ground a n d . e x c i t e d e l e c t r o n i c s t a t e a r e n o t d i s p l a c e d , a r e a s o n a b l e assumption i n t h i s case s i n c e no p r o g r e s s i o n i s observed.. A l o n g 20-cm  1  91 sequence  i s observed i n t h e vapour spectrum.  t h e 119-cm  1  I f t h i s sequence  involves  fundamental, the i n t e n s i t y o f the overtone i n the e l e c t r o n i c  spectrum a c c o r d i n g t o e q u a t i o n (7.1) i s about 0.5% o f t h e o r i g i n  band.  A p p a r e n t l y , t h e p r e s e n c e o f o t h e r i n t e r a c t i o n s i s r e q u i r e d t o account f o r the f u l l i n t e n s i t y o f t h i s  band.  Chapter 8 A V i b r a t i o n a l Assignment  o f Dibenzothiophene-h  c  and  o Dibenzothjophene-d  from I n f r a r e d and Raman S p e c t r a  o A.  Introduction An assignment o f t h e fundamental v i b r a t i o n s o f d i b e n z o t h i o p h e n e based  on i n f r a r e d and Raman s t u d i e s has n o t been p r e v i o u s l y a t t e m p t e d . the c r y s t a l s t r u c t u r e o f d i b e n z o t h i o p h e n e has been d e t e r m i n e d ^  1  However, and l a r g e  c r y s t a l s a r e e a s i l y grown from t h e melt so t h a t i t i s p o s s i b l e t o o b t a i n p o l a r i z e d i n f r a r e d and Raman d a t a .  I t i s a l s o f o r t u n a t e that dibenzothiophene-d  i s r e a d i l y s y n t h e s i z e d from b i p h e n y l - d ^ so t h a t a more complete s t u d y o f the v i b r a t i o n s of dibenzothiophene i s p o s s i b l e .  The assignment o f t h e  fundamental v i b r a t i o n s from t h i s d a t a p r o v i d e s not o n l y a u s e f u l  comparison  w i t h t h e assignments o f c a r b a z o l e and f l u o r e n e , b u t a l s o a f u r t h e r check 73 on t h e t r a n s f e r a b i l i t y o f t h e phenanthrene  force f i e l d  which p r o v e d  s a t i s f a c t o r y i n t h e c a r b a z o l e normal c o o r d i n a t e c a l c u l a t i o n . B.  S e l e c t i o n Rules D i b e n z o t h i o p h e n e c r y s t a l l i z e s i n t h e m o n o c l i n i c system w i t h space  ^2h  group  ^ 2 j / c ) T h e p o s i t i o n s o f t h e f o u r m o l e c u l e s i n t h e u n i t c e l l , and  t h e r e l a t i v e d i s p o s i t i o n s o f t h e m o l e c u l a r axes directions  (x_>y,z)  ,  the extinction  (j_,b_,s_) i n t h e c r y s t a l , and t h e c r y s t a l l o g r a p h i c axes  shown i n F i g . 9.  (<a,b_,c) a r e  The d i b e n z o t h i o p h e n e m o l e c u l e i s s l i g h t l y n o n - p l a n a r w i t h  t h e two benzene r i n g s f o r m i n g an a n g l e o f 178.7°.  The d e v i a t i o n from  - 154 p l a n a r i t y which may be due t o p a c k i n g f o r c e s the f r e e molecule i s treated  as h a v i n g C^  i n t h e c r y s t a l i s s m a l l and  symmetry.  v  The s e l e c t i o n r u l e s f o r t h e f r e e m o l e c u l e and f o r t h e u n i t c e l l modes are s e t out i n t h e c o r r e l a t i o n diagram o f T a b l e 33.  From t h e T a b l e , i t i s  c l e a r t h a t each f r e e m o l e c u l e v i b r a t i o n s p l i t s i n t o f o u r u n i t c e l l modes f o r k = 0 such t h a t  T a b l e 33.  two a r e i n f r a r e d a c t i v e and two a r e Raman a c t i v e .  Correlation  t a b l e showing t h e s e l e c t i o n r u l e s f o r t h e i s o l a t e d  m o l e c u l e and t h e c r y s t a l o f d i b e n z o t h i o p h e n e .  N  2v  C  20 9  xy  A  2  9  zx  B  l  19  TL  rr,bb,ss,rs  ,A  l |  A  2h  n. 6  g  \\ )A  [ u  V  'B  u  rb,sb  6  b  5 4  J_,5  N i s t h e number o f fundamentals i n t h e f r e e m o l e c u l e and n i s t h e number o f l a t t i c e f r e q u e n c i e s w i t h k_ = 0.  An a s s u m p t i o n , based on t h e s i m i l a r i t y o f t h e i n f r a r e d and Raman s p e c t r a o f t h e s o l u t i o n and c r y s t a l , i s t h a t t h e i n t e r m o l e c u l a r are  interactions  s m a l l so t h a t t h e o r i e n t e d - g a s model may be used t o p r e d i c t t h e  p o l a r i z a t i o n r a t i o o f t h e c r y s t a l bands.  In t h i s a p p r o x i m a t i o n , the  r e l a t i v e i n f r a r e d band i n t e n s i t i e s a l o n g t h e _r,£, and £ axes a r e t a b u l a t e d i n Table 34. E v i d e n t l y ,  t h e 19  t o appear almost e x c l u s i v e l y  modes o f t h e f r e e m o l e c u l e a r e expected  a l o n g t h e r_ a x i s .  The 20 fundamentals  of the  A^ type s h o u l d be about t h r e e times s t r o n g e r a l o n g t h e b_ t h a n t h e £ a x i s , and t h e 9 B  fundamentals  t h r e e times s t r o n g e r a l o n g t h e £ t h a n t h e b_ a x i s .  - 155 -  Table  34.  R e l a t i v e band i n t e n s i t i e s a l o n g t h e c r y s t a l - axes  calculated f o r  t h e o r i e n t e d - g a s model.  r  0 0050  0.0153  0 9824  b  0 7777  0.2223  0 0001  s  0 2195  0.7625  0 0175  The r_. and _s_ axes a r e d e f i n e d i n chapt e r 2.  I n a m o n o c l i n i c system w i t h s i t e group  even t h e o r i e n t e d - g a s  model does n o t p r e s e n t a s i m p l e p i c t u r e o f " t h e i n t e n s i t y d i s t r i b u t i o n o f t h e Raman s c a t t e r i n g among t h e p o s s i b l e p o l a r i z a t i o n arrangement's. squares  The  o f t h e elements o f t h e p o l a r i z a b i l i t y t e n s o r t r a n s f o r m e d from t h e  3c,v_,z_ m o l e c u l a r frame t o t h e £^]"ss_ c r y s t a l frame r e l a t e t h e r e l a t i v e i n t e n s i t i e s o f - t h e f r e e m o l e c u l e Raman a c t i v e modes t o t h e u n i t c e l l Raman a c t i v e modes.  The r e s u l t s o f t h i s c a l c u l a t i o n f o r d i b e n z o t h i o p h e n e  are incorp-  orated i n the equation: f  I SS  I  0. 5813  0 0003  0 0482  0 0534  0.6691  0. 0154  0. 0002  0 9653  0 0000  0 0599  0.0003  0. 0195  rr X  XL  bb  I rs J  PJL  •*rb  k  XX  i  0. 0494  0 0000  0 6048  0 0001  0.6916  0. 0003  0. 0116  0. 0172  0 0010  0. 7210  0.0000  0. 2244  0. 1695  0 0000  0 1707  0 0050  0.3016  0. 0127  Q- 003.4  0 0001  0 0004  0 2174  0.0202  0. 7562  zz xy xz •  yz_.  (8.1)  C.  The  Infrared  156 -  Spectrum  /  The polarized  i n f r a r e d spectra  of dibenzothiophene c r y s t a l recorded  l i g h t i n c i d e n t on the r s and b r f a c e s are shown i n F i g . 33  34.  These s p e c t r a  with  the s o l u t i o n spectrum i n F i g . 35 and  between i n t e r - and  are p a r t i c u l a r l y crowded w i t h bands so t h a t  intra-molecular  a s c e r t a i n whether two  oppositely  36 was  modes i n the  free molecule v i b r a t i o n s .  The  necessary to d i s t i n g u i s h low f r e q u e n c y r e g i o n  s o l u t i o n and  f o l l o w i n g assignments: 1  In the s p e c t r a  c o r r e l a t e w i t h two  and  bands w i t h the and  1594  1072  1305  (A ) cm  1  and  712  s e p a r a t e bands i n the s o l u t i o n at 701  and  706  cm , -1  1309  (A ) y  and  ( i i i ) the cm  1074  c r y s t a l w i t h the  1314  1594  s o l u t i o n band and  the 499  (B ) cm  279  (B ) and  cm  1  1317  s o l u t i o n band.  1  which has  suggests t h a t they may been i n d u c e d by  considerations  cm  s h i f t o f 21 cm  (B ) and  282  (A ) cm  1  1  \  crystal  -1  1589  (B )  In the  low  .band c o r r e l a t e s w i t h the 495 520  (A )  solution  (A ) c m  ( i v ) the  appear i n the s o l u t i o n i n f r a r e d spectrum i s u n c e r t a i n . cm  u  w i t h the  1  ''"crystal band w i t h the  l a t t e r case the s o l v e n t  assignment o f the  (B ) cm  s o l u t i o n bands, and  1  (A ) c r y s t a l  287  clarified  and  the 494  The  t h i s reasoning  c r y s t a l bands at 704  frequency r e g i o n ,  a l t h o u g h i n the  i n the rs_ p l a n e  (B )  ( i i ) the c r y s t a l bands at 1068 bands at 1066  I t i s r e a d i l y deduced from  (A ) and  shown i n F i g . 34,  ( i ) The  independent  show a s p l i t t i n g i n the c r y s t a l  between the components a c t i v e a l o n g the b_ a x i s  the  to  c r y s t a l i n f r a r e d data together  T a b l e 33 t h a t a f r e e m o l e c u l e v i b r a t i o n may  component).  and  p o l a r i z e d bands are f a c t o r group compon-  w i t h t h e i r assignments are c o l l e c t e d i n T a b l e 35".  (B  and  a comparison  e n t s o f the same f r e e m o l e c u l e v i b r a t i o n or c o r r e s p o n d t o two  cm  with  cm  1  s o l u t i o n band  i s rather  large.  bands which do  not  A Raman l i n e at  be f a c t o r group components of a fundamental  crystal forces.  However, a c c o r d i n g t o t h e o r e t i c a l  a v i b r a t i o n d e r i v i n g i t s i n t e n s i t y by m i x i n g w i t h  intense  -  157 -  bands nearby i s n o t e x p e c t e d t o show s p l i t t i n g s .  27  f a v o u r e d h e r e i s t h a t t h e 279 (B ) and 282 ( A ) cm u  c o m b i n a t i o n bands.  T h i s may i m p l y t h a t an A  w i t h t h e B j fundamental a t 138 cm As i n p r e v i o u s c h a p t e r s ,  2  Thus, t h e assignment 1  bands a r e independent  fundamental i s almost degenerate  \  the l a t t i c e modes i n T a b l e s 35 and 36 a r e  d i s t i n g u i s h e d from i n t r a m o l e c u l a r modes by t h e use o f lower case symbols. Two b - p o l a r i . z e d l i n e s o f a^ symmetry were observed a t 89 and 109 an and a t h i r d band was l o c a t e d a t 72 cm^  1  w i t h some u n c e r t a i n t y s i n c e the measurement  were made on a c r y s t a l w h i c h was somewhat t h i n n e r and had a s m a l l e r area than i s r e q u i r e d f o r the r e c o r d i n g o f l a t t i c e v i b r a t i o n s . l a t t i c e frequencies  20O  300  •>  33  Only two  .  1  Fig.  surface  o f t h e b^ t y p e were observed i n . t h e a£ p l a n e a t 53 and  about 103 cm .  CO.  \  400  *X>  600  TOO  • wavenumber (cm-')  The p o l a r i z e d i n f r a r e d spectrum o f d i b e n z o t h i o p h e n e i n t h e low frequency region.  D o t t e d l i n e / / r ; s o l i d l i n e //b_.  400 Fig.  6QO 34  800  IOOO  1200  1400  The i n f r a r e d s p e c t r a o f d i b e n z o t h i o p h e n e s i n g l e c r y s t a l , (b) D o t t e d l i n e //b; s o l i d l i n e / / r .  1600  1800  Cm"  1  (a) D o t t e d l i n e //s_; s o l i d l i n e / / r _ .  - 159 -  100  F i g . 35  200  300  400  600 cm"  500  The i n f r a r e d spectrum o f d i b e n z o t h i o p h e n e i n c y c l o h e x a n e  1  (solid  l i n e ) and benzene (broken l i n e ) s o l u t i o n s i n t h e low f r e q u e n c y region.  II —I 600  , 800  , IOOO  , 1200  :  , WOO  yf.  ,  ,  ,  1600  1800  2COO  !  :—  3COO  32CO  . wavenumber (cm ) -1  F i g . 36  The i n f r a r e d spectrum o f d i b e n z o t h i o p h e n e i n carbon carbon t e t r a c h l o r i d e and t e t r a c h l o r o e t h y l e n e  disulphide,  solutions.  _ 160  T a b l e 35.  The i n f r a r e d  spectrum o f d i b e n z o t h i o p h e n e i n t h e c r y s t a l and  solution.  Solution  //r  •//b  //s  53 w  53 w 72 vw? 89 m  104 w  101 w 109 vw  121 s  138 vw  210 m 224 s  229 w  416 s  425 w  B  213 s  218 mw  k  224 ms  228 ms  B B  2  comb?  282 m  A  1  comb?  403 s  Aj  417 m  424 s  Bj  433 vw  433 w  B  comb  1  A^ comb  462 vw  520 ms  u a u a u b u a u  138 s  456 vw  495 s  b  137 ms  279 w  405 m  Symmetry  B  2  A  1  496 m  B  2  560 vw  B  2  B  2  B  2  494 m 499 m 508 sh 559 m  608 m  612 m  701 m  704 s  706 mw 739 vs  561 mw  705 w 712 sh 735 v s  726 vw 753 in  711 sh 744 vs 724 vw  768 s 773 vw  770 s  ,  772 s  A. 794 vw  850 w  A  Bj B, ?  .  854 vw  _  B  1  Aj  - 161 -  Solution  930 mw  //r  //b_  //s 859 mw  B  l  865 m  872 mw  866 m  B  2  891 w  900 w  890 w  B  l  934 s  934 s  934 vw  A  l  940 s  B  l  B  2  966 s 970 s 992 w  988 m  1000 sh  1001 m  1024 s  1028 s  973 m  992 m  1066 m  B  2  1026 s  1026 mw  A  l  1054 w  1053 vw  A  l  B  2  A  l  1068 s 1074 s  1072 m  1121 vw  1120 sh  1134 s  1132 s  1155 mw  2 l  B  2  1132 vw  A  l  1156 ms  1155 m  2 A B  1166 w  1163 vw  B  1179 vw  r  V B  1196 w  1201 m  1203 ms  1203 m  1226 s  1232 m  1233 vs  1235 s  1262 w  1268 ms  1265 mw  1270 w .  1282 vw 1305 sh  B  A  1145 sh 1157 m  i  1000 vw  1105 vw 1131 m  V A  1063 vw 1072 s  Symmetry  1314 s  2  l A. i A  B  2  A  l  1313 ms  B  2  1309 s  1317 s  1320 m  A  l  1334 vw  1335 m  1533 vw  A  l  1353 m  B  1393 vw  2  B  2  A  l  B  2  1350 vw 1412 w  1415 w 1417 vs  1424 s 1442 s  1442 s  1425 s  1 ?  - 162 -  Solution 1454 m  //s  1475 mw  1476 vw  Symmetry  1462 s  1466 w 1497 sh 1510 w  //b 1493 mw  1514 m 1557 m  1555 w 1564 vw  1577 vw 1594 s  1589 s  1594 s  1592 mw  1627 mw  1629 vw  1600 w 1620 w  1623 mw  1638 sh  A,  1645 vw 1662 mw 1676 vw  1681 m  1677 mw  1703 vw  1706 m  1705 mw  1739 w  1734 vw  1780 w  1781 ms  1782 m  1792 w  1793 sh  1793 sh  1816 m  1817 w  1826 w  1826 w  1829 vw  1896 sh  1897 sh  1899 sh  1899 w  1907 m  1907 ms  1909- mw  1935 w  1937 ms  1934 mw  1937 w  1780 w  1815 vw  1864 vw  1708 vw  1871 m  1973 w 2880 w 2893 w 2995 vw 3010 vw 3025 w  3000 sh 3020 s 3025 sh  3055 sh  3025 vw  A,  - 163 -  Solution  //r  //b  //s  3063 v s  3055 v s  3055 vs  3055 ms  3121 vw  3117 mw  D.  Symmetry  Raman S p e c t r a Raman s p e c t r a o f d i b e n z o t h i o p h e n e c r y s t a l r e c o r d e d f o r a l l p o s s i b l e  p o l a r i z a t i o n arrangements o f t h e i n c i d e n t and s c a t t e r e d i n F i g . 37 and 38.  l i g h t a r e reproduced  The d e p o l a r i z a t i o n r a t i o s o f t h e Raman l i n e s which  were measured i n a carbon t e t r a c h l o r i d e s o l u t i o n a r e shown i n T a b l e 37 t o g e t h e r w i t h t h e c r y s t a l d a t a and t h e symmetry assignments o f t h e bands.  _ 164 _  (rr)  | O  r  ~  1  200  1  •  1  400  1  1 600  1  1 800  1  1  1  IOOO  1  1  1200  wavenumber ( cm ) -1  F i g . 37  Raman s p e c t r a o f d i b e n z o t h i o p h e n e  1 1400  1  1—7/ 1600  '  | 3000  '  1 32CO  (sb)  — i —  400  600  —1—'—1—•—1— —1——1—1—7,—1—'—1  eoo  000  120c  woo  e o o  3000  3200  wavenumber (cm ') -  F i g . 38 Raman s p e c t r a o f d i b e n z o t h i o p h e n e s i n g l e  T a b l e 36.  Raman spectrum o f d i b e n z o t h i o p h e n e i n carbon s o l u t i o n and a s i n g l e  CC1,  crystal.  P  tetrachloride  crystal.  Crystal  Symmetry  138 171 218  l  A  235 277 w  ~ 0.75  286 '308  '406 ms  0.17  410  1  l A, A  - 166 -  CC1,  P  Crystal  Symmetry  421 438 498 505 704 s  0.14  704 730 747 771  A  l  V  939 1002 1025 v s  0.09  1027  1070 w  0.53  1072 1122  1134 ms 1160 vw  ^  0.24  1137  0.75  1172 1204  1230 ms  0.21  1236 1294 1315  1318 vs  0.21  1321 1337  l A, A  1422 1433 1480 m  0.31  1480  1560 w  0.54  1558 1566 1580 1590  1605 s  0.44  1601 1618  3066 mw  0.0  3060  A,  - 167 -  According to the oriented-gas p r e d i c t i o n s i n equation (8.1), the t o t a l l y symmetric v i b r a t i o n s a r e expected t o dominate t h e ( r r ) spectrum, and t h e A^ as w e l l as t h e  modes s h o u l d appear w i t h about e q u a l r e l a t i v e  s t r e n g t h s i n b o t h t h e (bb) and ( s s ) s p e c t r a .  I t s h o u l d be n o t e d , however,  t h a t t h e t o t a l l y symmetric v i b r a t i o n s have t h e g r e a t e s t i n t r i n s i c (see t h e s o l u t i o n d a t a i n T a b l e 3~6) .  strength  With t h e a i d o f t h e d e p o l a r i z a t i o n  r a t i o s , t h e A^ l i n e s i n T a b l e 36 were f i r m l y a s s i g n e d .  The B^ bands were  a s s i g n e d w i t h p a r t i c u l a r r e f e r e n c e t o t h e ( r b ) spectrum i n which they a r e p r e d i c t e d t o have most o f t h e i r r e l a t i v e i n t e n s i t y , a f t e r s u b t r a c t i n g out t h e c o n t r i b u t i o n s from t h e t o t a l l y symmetric  lines.  On t h e b a s i s o f t h e Raman s p e c t r a i n F i g . 37 and 38, t h e 235 cm cannot be a s s i g n e d .  1  band  However, i t was t e m p t i n g t o a s s i g n t h e l i n e as a B^  s p e c i e s s i n c e a 226 cm  1  band appeared i n t h e i n f r a r e d spectrum.  were t h e c a s e , however, t h e 235 cm and not i n t h e ( r s ) spectrum.  1  I f this  l i n e s h o u l d appear i n t h e (bb) spectrum  I t i s u n l i k e l y that misalignment of  t h e c r y s t a l can account f o r t h e observed r e s u l t s so t h a t a p p r e c i a b l e c r y s t a l m i x i n g o f t h e A-^ and B^ fundamentals has p r o b a b l y t a k e n p l a c e . The appearance o f a l i n e a t 287 cm  1  i n t h e ( r b ) and ( r s ) s p e c t r a  f a v o u r s a B^ assignment, b u t t h i s i s brought i n t o q u e s t i o n by i t s appearance i n t h e ( s s ) and (sb) s p e c t r a as w e l l . by a comparison w i t h t h e 299 cm  1  The s i t u a t i o n i s f u r t h e r c o m p l i c a t e d  c a r b a z o l e band and a 288 cm  1  f l u o r e n e band  b o t h o f which have A^ symmetry. The weak s a t e l l i t e bands a t 1122, 1294, 1337, and 1618 cm  f o r example,  are p r o b a b l y c o m b i n a t i o n bands d e r i v i n g t h e i r i n t e n s i t y from t h e s t r o n g bands nearby.  _ 168 _  E.  Raman A c t i v e L a t t i c e Modes The l a t t i c e v i b r a t i o n s shown i n F i g . 37 and 38 a r e q u i t e s t r o n g , and  were r e c o r d e d under c o n d i t i o n s which reduced t h e i n t e n s i t y o f t h e bands by a f a c t o r o f about t h r e e compared w i t h t h e r e s t o f t h e spectrum.  The  l a t t i c e f r e q u e n c i e s and t h e i r assignments are t a b u l a t e d i n T a b l e 37.  T a b l e 37.  Raman spectrum o f d i b e n z o t h i o p hene near t h e e x c i t i n g l i n e .  (bb)  (rr)  (ss)  (IS)  (bl)  (bs)  Symmetry  34  33  32  64  64  a ,b g ;.e a .g b .g a ,b  49  78  79  104  78  79  81  80  104  104  104  104  g'/g  a ,b g g b ? .g  126  In a r e c e n t p a p e r ,  t h e Raman a c t i v e l a t t i c e v i b r a t i o n s o f anthracene  and n a p h t h a l e n e which a r e a l l due t o l i b r a t i o n a l modes ( h i n d e r e d r o t a t i o n s ) were a d e q u a t e l y accounted f o r by c o n s i d e r i n g t h e r o t a t i o n a l about t h e t h r e e p r i n c i p a l axes o f t h e m o l e c u l e .  oscillations  I t i s i n t e r e s t i n g t o use  t h i s method i n i n t e r p r e t i n g t h e low f r e q u e n c y Raman a c t i v e modes.  In  m o n o c l i n i c c r y s t a l s w i t h f o u r m o l e c u l e s i n t h e u n i t c e l l , s i x Raman a c t i v e l i b r a t i o n a l modes appear i n t h r e e p a i r s ; each p a i r c o n s i s t s o f an a  and b  mode (see T a b l e 33) . The r o t a t i o n a l o s c i l l a t i o n s about t h e x_, y_, z_ axes o f the m o l e c u l e t r a n s f o r m l i k e t h e B^, B^, and o f t h e C,  m o l e c u l a r p o i n t group.  irreducible representations  S i n c e a r o t a t i o n a l o s c i l l a t i o n about a  - 169 principal  molecular  a x i s and an i n t r a m o l e c u l a r v i b r a t i o n  belonging  t o the  same symmetry s p e c i e s a r e expected t o behave i n t h e same manner, t h e relative  intensity  distribution  o f a l i b r a t i o n a l mode among t h e v a r i o u s  p o l a r i z e d s p e c t r a can be deduced f r o m - e q u a t i o n ( 8 . 1 ) . appropriate  T a b l e 38.  For c l a r i t y the  e n t r i e s a r e t a b u l a t e d i n T a b l e 38.  o f Raman a c t i v e modes due t o  Relative intensities oscillations  about t h e x_,  z -molecular  rotational  axes among t h e  various polarized spectra.  w  w  w  (rr)  0..0195  0.. 0005  0.,0599  (bb)  0,.0003  0..6916  0.,0001  (ss)  0..0154  0..6691  0..0534  (rb)  0..7562  0..0202  0..2174  (rs)  0..2244  0..0000  0.,7210  (bs)  0..0127  0..3016  0,.0050  T r e a t i n g t h e l i b r a t i n g m o l e c u l e as a harmonic o s c i l l a t o r , t h e frequency o f o s c i l l a t i o n  (v) i s  v  where k i s t h e f o r c e c o n s t a n t of  1 k =27( )  1 / 2  (8.2)  T  and I t h e moment o f i n e r t i a .  S i n c e t h e moments  i n e r t i a o f t h e d i b e n z o t h i o p h e n e m o l e c u l e about t h e x, z_, y_ axes  decrease i n that order, equation  (8.2) p r e d i c t s t h a t t h e l i b r a t i o n a l  - 170 -  f r e q u e n c i e s a l s o i n c r e a s e i n t h e same o r d e r .  I f only the three strongest  l a t t i c e modes a r e c o n s i d e r e d , t h i s s i m p l e treatment  of the origins of the  l i b r a t i o n a l modes i s i n agreement w i t h t h e f o l l o w i n g o b s e r v a t i o n s : lowest f r e q u e n c y  l i n e a t 33 cm  1  ( i ) The  was c o r r e c t l y p r e d i c t e d t o appear w i t h most  o f i t s i n t e n s i t y i n t h e (rb) spectrum and some o f i t s i n t e n s i t y i n t h e ( r s ) spectrum; ( i i ) t h e i n t e r m e d i a t e f r e q u e n c y  a t 79 cm  1  w i t h most o f i t s  i n t e n s i t y i n t h e ( r s ) spectrum and w i t h some i n t e n s i t y i n t h e (rb) spectrum; and  ( i i i ) t h e h i g h e s t frequency  a t 104 cm  1  appeared w i t h about  equal  i n t e n s i t y i n t h e (bb) and (ss) s p e c t r a , and w i t h reduced i n t e n s i t y i n t h e (sb_) spectrum.  F.  Assignment o f Fundamentals The  c r i t e r i a f o r s e l e c t i n g a fundamental were p r e v i o u s l y d i s c u s s e d i n  c o n n e c t i o n w i t h t h e assignment o f t h e c a r b a z o l e and f l u o r e n e fundamental vibrations. A^ Symmetry There a r e 20 fundamental v i b r a t i o n s b e l o n g i n g t o t h e A^ s p e c i e s ; 16 o f t h e s e modes a r e expected  t o have f r e q u e n c i e s l e s s than 2000 cm . 1  In the  i n f r a r e d spectrum, t h e s t r o n g l i n e s a t 215, 403, 494, 712, 934, 1026, 1068, 1133,  1203, 1233, 1318, 1421, 1557 and 1593 cm"  mentals.  These assignments were supported  symmetry observed 1559,  1  were a s s i g n e d as A  1  funda-  by t h e Raman bands o f A^  at 218, 409, 498, 704, 1027, 1071, 1136, 1238, 1321, 1479,  and 1601 cm . 1  The f r e q u e n c y  d i f f e r e n c e s between t h e bands common t o  b o t h t h e i n f r a r e d and Raman spectrum a r e w i t h i n t h e a l l o w a b l e l i m i t s o f experimental  accuracy  and f a c t o r group s p l i t t i n g .  account f o r 15 o f t h e 16 f u n d a m e n t a l s .  The two s e t s o f v i b r a t i o n s  The l a s t A^, fundamental was l o c a t e d  as t h e strongest, l i n e i n t h e phosphorescence spectrum a t 849 cm . 1  The  - 171 counterpart  o f t h e 849 cm  i n t e r v a l i n t h e i n f r a r e d spectrum i s the weak  1  band a t 854 cm A l t h o u g h a f a i r l y s t r o n g i n f r a r e d l i n e a t 1156 cm  1  appears t o have A^  symmetry, i t was r e j e c t e d as a fundamental f o r t h e f o l l o w i n g r e a s o n s : ( i ) The d e p o l a r i z a t i o n r a t i o o f t h e Raman l i n e a t 1160 cm  1  i n d i c a t e d t h a t i t was  n o n - t o t a l l y s y m m e t r i c , ( i i ) t h e band d i d n o t have any a c t i v i t y i n e i t h e r t h e f l u o r e s c e n c e o r phosphorescence  spectrum.  Three o f t h e f o u r CH s t r e t c h i n g f r e q u e n c i e s were t e n t a t i v e l y p l a c e d a t 3000, 3025, and 3055 cm .  Better resolved infrared spectra of thinner  1  c r y s t a l s a r e needed t o improve t h i s B  2  assignment.  Symmetry The 15 B  assigned  2  fundamentals w i t h f r e q u e n c i e s l e s s t h a n 2000 cm  from t h e r - p o l a r i z e d i n f r a r e d spectrum.  f a i r l y intense or w e l l separated  were  1  Bands which were e i t h e r  from o t h e r s t r o n g e r bands were observed a t  560, 613, 865, 966, 1001, 1268, 1353, 1442, 1462, and 1514 cm" ; 1  f r e q u e n c i e s were a s s i g n e d  as  fundamentals.  these  With t h e a i d o f t h e i n f r a r e d  s o l u t i o n s p e c t r u m , t h e r _ - p o l a r i z e d bands a t 496, 704, 1074, and 1314 were i d e n t i f i e d as s e p a r a t e  cm  -1  l i n e s which were not f a c t o r group components o f  A j o r B^ l i n e s , and were a l s o a s s i g n e d as B^ f u n d a m e n t a l s .  The p r e v i o u s l y  d i s c u s s e d 1156 cm  fundamental  1  i n f r a r e d band was f a v o u r e d  sought s i n c e i t b r i n g s the B  2  as t h e f i n a l  fundamental b l o c k o f f r e q u e n c i e s  into close  c o r r e s p o n d e n c e w i t h t h o s e o f c a r b a z o l e and f l u o r e n e (see Appendix I I ) . The comment on t h e need f o r b e t t e r i n f r a r e d s p e c t r a t o l o c a t e t h e A^ CH s t r e t c h i n g f r e q u e n c i e s a l s o a p p l i e s t o t h e a s s i g n i n g t h e f o u r B s t r e t c h i n g fundamentals.  2  The i n f r a r e d bands a t 3025, 3055 and 3117  were thought t o mark t h e p r e s e n c e o f t h r e e B_ f u n d a m e n t a l s .  CH cm"  1  - 172 Symmetry The assignment o f t h e i n f r a r e d spectrum.  fundamentals must r e s t e n t i r e l y on t h e p o l a r i z e d  Seven fundamentals were l o c a t e d a t 138, 226, 4 2 1 , 744,  770, 859, and 940 cm .  A f a i r l y weak band a t 895 cm  1  1  which was w e l l  s e p a r a t e d from o t h e r bands was a s s i g n e d as a n o t h e r f u n d a m e n t a l .  Of t h e  two p o s s i b l e B^ fundamentals a t 724 and 794 cm , t h e l i n e a t 724 cm 1  1  was  a r b i t r a r i l y s e l e c t e d t o make up t h e f u l l complement o f B^ f u n d a m e n t a l s . A  2  Symmetry None o f t h e A  2  fundamentals were i d e n t i f i e d i n t h e Raman spectrum.  p r e v i o u s l y p o i n t e d o u t , t h e l i n e a t 287 cm  1  may be t h e analogue o f t h e A  Raman a c t i v e fundamental i n f l u o r e n e a t 287 cm  As 2  and i n c a r b a z o l e a t 299  1  -1 cm  G.  I n f r a r e d and Raman S p e c t r a o f D i b e n z o t h i o p h e n e - d g A complete s t u d y o f t h e d i b e n z o t h i o p h e n e - d  crystal requires a polarized 8  i n f r a r e d spectrum o f t h e r s - c r y s t a l f a c e i n o r d e r t o d i f f e r e n t i a t e between A^ and B^ f r e q u e n c i e s , and a s o l u t i o n Raman spectrum t o p r o v i d e d e p o l a r i z a t i o n r a t i o s t o a s s i s t i n s o r t i n g t h e t o t a l l y symmetric from t h e n o n - t o t a l l y symmetric v i b r a t i o n s . The i n f r a r e d s p e c t r a  w i t h p o l a r i z e d l i g h t i n c i d e n t on t h e r b - c r y s t a l  f a c e are shown i n F i g . 39 and 40, and t h e f r e q u e n c i e s t o g e t h e r w i t h t h e i r assignments a r e l i s t e d i n T a b l e 39.  An i n f r a r e d spectrum i n carbon t e t r a -  c h l o r i d e , carbon d i s u l p h i d e , and t e t r a c h l o r o e t h y l e n e s o l u t i o n ( F i g . 41) was r e c o r d e d i n t h e r e g i o n 550-2400 cm , and i n c y c l o h e x a n e s o l u t i o n 1  i n t h e r e g i o n 80-700 cm . 1  ( F i g . 42)  The r e s u l t s a r e i n c l u d e d i n T a b l e 39, and were  used t o d i s t i n g u i s h between d i s t i n c t o p p o s i t e l y p o l a r i z e d bands and f a c t o r group components o f a s i n g l e f r e e m o l e c u l e band.  i  1 400  1  1  1  600  n 800  1  1 1000  1  ~i  1  1200  WAVENUMBER  F i g . 40  1 1400  1  1 1600  1  i 1800  i  i  r~~  2000  2500  (cm" ) 1  I n f r a r e d s p e c t r a o f dibenzothiophene-d„, c r y s t a l t h i c k n e s s 0.32 mm; s o l i d l i n e / / b ,  o broken l i n e / / r .  —  1  1  600  8 0 0  1  IOOO  1  1  I200  I400  1  1600  •  1  1800  1  2 0 0 0  1  2200  wavenumber (cm ') -  F i g . 41  I n f r a r e d spectrum o f d i b e n z o t h i o p h e n e - d g i n carbon d i s u l p h i d e , carbon t e t r a c h l o r i d e , and tetrachloroethylene solutions.  I  2400  100  F i g . 42  200  300  400  500  60ocm  I n f r a r e d spectrum o f d i b e n z o t h i o p h e n e - d _ i n c y c l o h e x a n e s o l u t i o n , i n the l o w - f r e q u e n c y  _  region.  - 177 -  T a b l e 39.  Solution  The i n f r a r e d spectrum o f d i b e n z o t h i o p h e n e - d g  //b_  //r_  Symmetry  52 m  b  71 w  b  u u 87 m  a  u 101 vw  b  u 106 w  a  u 115 m  126 vs  130 m  B  135 sh  ?  150 mw  ?  196 m  198 261 vs s  201 wm 258  215 s  215 286 wvs  219 m  366 vs  363 s  372 m  390 m  388 ms  391 vw  403 vw  . 402 w  417 vw  B  B  A  V  B  B  2  453 mw  B  1  472 ms  B  2  484 ms  480 sh  A  J  494 w  490 s  B„  508 vw  508 vw  A  445 s  i  1  B,  '  B  A  438 vw  522  1' 1 B  516 vw  B  542 vw  B'  2  mw  i  593 w  V i i»i ' i l  B,  475 mw  561 s  A  A  419 vw  435 sh  449 s  1  561 ms  B  566 ms  S  1  ,B^  571 ms  B  2  583 w  B  2  592 s  B2  -  Solution  178  -  598 614  w  622  mw  631  vw  713  750  664  m  m  727  m  844  672  vs  709  vw  s.  723  mw  748  761  ms  763  w  775 vvw  840  sh  845  ras  886  940  vvw  w vvw  911  ms  956  vvw  ms  991  vvw  V2 B  s  886  vw  895  vw  910  w  948  s  vw  w 1014 mw  1021  1040  vs  1045  1051  vw  1056  vw  978  w  993  w  s  A  I  B  2  B  2  l  A  1015 vw  B  V  sh w  r i  A  A; ,I  vw  978  1015  Vi  s  965 972  B  ms  895 vvw  Vi  m  866  907  s  815  833  m  ms  791  854 860  B  B  w  w  11  A  m  w  ms 828  835  vw  s  791  806  2  A, ,B 1  w  646  vw  804  B  V 11  749 777  sh  B  635  660  Symmetry  //r  //b  s  1040  vs  1063  sh  B  2  B  2  A  r i B  - 179 -  Solution  //b  Symmetry  //r 1063 sh  105S w 1078 w 1120 sh  V i B  1121 vw  1125 mw  V i B  1132 vw 1143 w  1143 vw  1154 w  1158 w  1160 s  1188 sh  1.175 mw  1199 m  1198 vs  1203 m  1215 w  1221 sh  1218 mw  1230 vw  1229 w  B  2  B  2  l A,  A  1243 w 1260 vw  1255 m 1265 w  1286 vs  1280 s  1320 vs  1320 vs  1335 w 1357 ms  1379 w 1417 mw  1286 v s  ;  1330 vs 1353 vw  1355 s  1371 sh  1369 sh  1382 sh  1380 m  1390 m  1390 sh  1416 ms  1417 vw  V i B  V i V i B  B  1435 vvw 1443 vvw  1447 vw  1446 m  1458 vvw  1465 w  1465 sh  1478 vw  1478 ms 1505 w  1533 w  1521 w 1530 m  1537 w 1555 sh 1564 ms 1576 m  1560 vs 1568 vs 1606 w  A  1' 2 B  -  Solution  ISO  -  //b  Hi.  1615 s  1614 w 1625 w  2 B  1736 w  B  2  1766 w  B  9  1767 mw  B  2  1806 w  B  2  1804 vw  B  2  V 1 B  1836 mw  V 1 B  2170 vw  B  2  2205 vw  B  2  2220 vw  A  l  2275 s  A  l  2284 s  2280 vs  B  2  A  l  2345 w  B  2  2365 sh  B  2  A  l  2315 sh  2380 vw  The p o l a r i z e d  B  V 1  1821 mw  2306 w  2 B  1713 mw  1803 sh  B  V 1 1688 mw  1763 vw  Symmetry  Raman spectrum o f dibenzothiophene-'d c r y s t a l i s r e p r o 8  duced i n F i g . 43 and 44; t h e f r e q u e n c i e s t o g e t h e r w i t h t h e i r assignments are  collected  i n T a b l e s 40 and 41. The assignment o f a Raman band i s  based on i t s r e l a t i v e i n t e n s i t y d i s t r i b u t i o n among t h e v a r i o u s arrangements as p r e d i c t e d by e q u a t i o n ( 8 . 1 ) .  polarization  181 ^  JV)JLA_  -A_  (ss)  V 20O  <JOO  6 0 0  800  OOO  I20O  1400  I 7/ BOO  1 2ZOO  1 24O0  wavenumber (crrr ) 1  F i g . 43  Raman s p e c t r a o f d i b e n z o t h i o p h e n e - d 8  T a b l e 40. The Raman spectrum o f d i b e n z o t h i o p h e n e - d  c r y s t a l near t h e e x c i t o  ing  (bb)  (r?)  line.  (ss)  (rs)  (br)  (bs)  Symmetry  31  32  31 42  a ,b g g a  77  .g a. ,b  46 6.1 79  78  77  101  100  127  127  79  71 99  99  cr o  a  <=•  a ,b  - 182  3 (sb)  -A i  O  1 —  2O0  1  400  Lv  1  eoo  COO  I2CO  I400  —T-//—I eOO  2200  ' 2400  wavenumber (cm ') -  F i g . 44  Raman s p e c t r a o f d i b e n z o t h i o p h e n e - d .  T a b l e 41. The Raman spectrum o f d i b e n z o t h i o p h e n e - d  Av(cm  Symmetry  Av(cm •*")  156  1057  202  1080  222  1125  251  1179  261  1196  269  1203  369  1224  crystal  Symmetry  l A A  l A, A  -  Av(cm  )  Symmetry  385  A  396  A  2 l  407  B  454  B  l  478  B  2  2  488  A  l  585  A  l  590  B  631  B  645  A  666  A  704  H.  183 -  2 l 2 l  746  l A  832  A  B  854  A  991  A  2 ?  l l l  The Assignment o f t h e Fundamentals  Av(cm  )  Symmetry  1233  A  l  1244  A  l  1287  A  1295  l B  1323  A  l  1340  B  2  1401  A  l  1420  A  l  1520  A  l  1542  B  2  1564  B  2  1575  A  l  2225  A  l  2271  A  l  2284  A  l  2309  A  l  2 ?  ?  o f Dibenzothiophene-d 8  A^  Symmetry In view o f t h e i n c o m p l e t e i n f r a r e d d a t a , t h e assignment o f t h e 20 A^  fundamentals must r e s t p r e d o m i n a n t l y on t h e Raman spectrum.  Of t h e 16 A^  fundamentals which a r e e x p e c t e d t o have f r e q u e n c i e s l e s s than 2000 cm , 1  t w e l v e were l o c a t e d as s t r o n g Raman bands i n t h e (bb) , ( r r ) , and ( s s ) s p e c t r a at 202, 396, 488, 666, 832, 854, 1057, 1203, 1287, 1421, 1529 and 1575 cm" . 1  E l e v e n o f t h e s e t w e l v e were prominent i n t h e i n f r a r e d spectrum, and were observed i n b p o l a r i z a t i o n a t 199, 390, 484, 664, 828, 866, 1059, 1201, 1283, 1417 and 1568 cm . 1  In t h i s l i s t ,  the mean o f t h e f a c t o r  group  • - 184 components was used where a p p l i c a b l e . i s o l a t e d i n f r a r e d band a t 911 cm  1  A moderately intense but f a i r l y  well  was thought t o r e p r e s e n t a n o t h e r A-^  fundamental a l t h o u g h i t was r e c o g n i z e d t h a t i t s l o c a t i o n i s w i t h i n t h e f r e q u e n c y r e g i o n marking t h e upper l i m i t f o r t h e also, may appear i n t h e same p o l a r i z a t i o n . at  1320 c m  - 1  fundamentals which  Even though  t h e i n f r a r e d band  has no c o u n t e r p a r t i n t h e Raman spectrum, i t was n e v e r t h e l e s s  a s s i g n e d as A^ on t h e b a s i s o f i t s i n t e n s i t y .  The two r e m a i n i n g A^ funda-  m e n t a l s were chosen from t h e m o d e r a t e l y weak i n f r a r e d bands a t 1125, 1179, 1255 and 1290 cm" . 1  The 1125 and 1179 cm"  1  bands were s e l e c t e d as the  r e q u i r e d fundamentals s i n c e t h e r e were c o r r e s p o n d i n g weak Raman a c t i v e bands w i t h A^ symmetry a t 1125 and 1175 cm . 1  The f o u r CH s t r e t c h i n g f r e q u e n c i e s were o b s e r v e d i n t h e Raman spectrum at B^  2271, 2284., 2309 and p o s s i b l y 2225 cm" . 1  Symmetry A c c o r d i n g t o th,e o r i e n t e d - g a s p r e d i c t i o n s  ( T a b l e 3 4 ) , t h e B^ f u n d a -  m e n t a l s a r e e x p e c t e d t o appear w i t h a r e a s o n a b l e i n t e n s i t y i n t h e b_p o l a r i z e d i n f r a r e d spectrum.  The i m p o r t a n t o b s e r v a t i o n here was t h a t t h e  more complete p o l a r i z e d i n f r a r e d spectrum o f d i b e n z o t h i o p h e n e - h  ( F i g . 34)  showed t h a t t h e B^ fundamentals were f a i r l y prominent i n t h e b - p o l a r i z e d i n f r a r e d spectrum.  Thus, t h o s e b - p o l a r i z e d i n f r a r e d bands which were  f a i r l y i n t e n s e i n t h e r e g i o n 100-900 cm  1  and d i d not have s t r o n g Raman  a c t i v e c o u n t e r p a r t s were a s s i g n e d as B^ f u n d a m e n t a l s .  The 9 fundamentals  were o b s e r v e d a t 128, 2.17, 366, 449, 561, 622, 720, 762, and 845 cm" . 1  B>2 Symmetry In t h e absence o f a p o l a r i z e d f l u o r e s c e n c e spectrum and l a c k o f c o r r o b o r a t i o n from t h e Raman s p e c t r u m , t h e o n l y b a s i s f o r t h e s e l e c t i o n o f  185-  fundamentals  was i t s i n t e n s i t y i n t h e _ r - p o l a r i z e d i n f r a r e d  spectrum.  Reasonable c o n f i d e n c e may be p l a c e d i n t h e f a c t t h a t t h e s t r o n g i n f r a r e d bands a t 472, 492, 592, 672, 775, 815, 833, 854, 948, 1160, 1286, 1335, 1446 and 1478 cm  1  r e p r e s e n t 14 o f t h e 15 B^ fundamentals  f r e q u e n c i e s l e s s t h a n 2000 cm . 1  expected t o have  The sample was f a r t o o t h i c k f o r t h e  i n f r a r e d r a d i a t i o n t o a d e q u a t e l y p e n e t r a t e t h e r e g i o n 1000-1600 cm  so  1  t h a t t h e p r e c i s e l o c a t i o n o f some o f t h e bands must await t h e r e s u l t s o f further experimentation.  The r e m a i n i n g B^ fundamental No B^ fundamentals  was q u i t e a r b i t r a r i l y  chosen as t h e 1380 cm  1  band.  r e g i o n beyond 1500 cm  1  s i n c e t h e h i g h e s t B^ fundamental  p r o t o n a t e d compound was 1520 cm  were a s s i g n e d i n t h e  and t h e v i b r a t i o n s  frequency i n the  o f the deuterated  s p e c i e s a r e expected t o be s h i f t e d t o lower f r e q u e n c i e s . The 2000-2500 cm  1  r e g i o n was not s u f f i c i e n t l y r e s o l v e d i n o r d e r t o  l o c a t e t h e f o u r CD s t r e t c h i n g A  2  frequencies with B  2  symmetry.  Symmetry The A  2  fundamentals  a r e expected t o be a c t i v e o n l y i n t h e Raman  (Table 41) w i t h most o f t h e i r i n t e n s i t y i n t h e ( r s ) spectrum 8.1).  S i n c e t h e Raman bands a t 156, 251, 645, and 746 cm  1  (see e q u a t i o n fulfil  r e q u i r e m e n t s , t h e y a r e a s s i g n e d as f o u r o f t h e n i n e A^ fundamental Raman A c t i v e L a t t i c e Modes o f  spectrum  these vibrations.  Dibenzothiophene-dg  In t h e r e g i o n near t h e e x c i t i n g l i n e , t h e c l o s e resemblance o f t h e Raman spectrum  o f dibenzothiophene-d  and -h„ i s not s u r p r i s i n g .  o  The  o  s i m p l e e x p l a n a t i o n l i e s i n i n t e r p r e t i n g t h e observed modes as r o t a t i o n a l o s c i l l a t i o n s i n t h e harmonic a p p r o x i m a t i o n .  Since the i n t e r m o l e c u l a r  f o r c e c o n s t a n t s a r e t h e same i n b o t h compounds, the r a t i o o f t h e f r e q u e n c i e s of t h e d e u t e r a t e d and p r o t o n a t e d s p e c i e s i n t h e harmonic a p p r o x i m a t i o n i s  - 186 -  V  H  D  I n s p e c t i o n o f T a b l e 42, which l i s t s t h e moments o f i n e r t i a o f the two isotopic ( Vp/v^j  s p e c i e s about t h e p r i n c i p a l m o l e c u l a r a x e s , shows t h a t t h e r a t i o ) i s v e r y c l o s e t o one i n a l l c a s e s .  T h i s accounts f o r t h e s i m i l a r -  i t y o f t h e low f r e q u e n c y r e g i o n s i n t h e two compounds.  3.  T a b l e 42.  Moments o f i n e r t i a about t h e m o l e c u l a r axes o f d i b e n z o t h i o p h e n e .  I  Compound  y  \  1927  510  1417  2119  561  1558  T  X  dibenzothiophene-h o dibenzothiophene-d o U n i t s x 10  I.  Normal C o o r d i n a t e  gm-cm  Calculation  The r e l e v a n t d e t a i l s p e r t a i n i n g t o t h e c a l c u l a t i o n o f t h e i n - p l a n e fundamental  frequencies of dibenzothiophene-h  Q  and -d  o o u t l i n e d f o r t h e c a r b a z o l e problem  i n c h a p t e r 3.  a n g l e s used f o r t h e c o n s t r u c t i o n o f t h e G-matrix  were p r e v i o u s l y o  The bond l e n g t h s and bond a r e shown i n F i g . 10.  The  i n - p l a n e i n t e r n a l c o o r d i n a t e d e f i n i t i o n s a r e i l l u s t r a t e d i n F i g . 45, and most o f t h e v a l u e s o f t h e f o r c e c o n s t a n t s a r e o b t a i n e d from T a b l e 11 which i s a p p l i c a b l e i f N i s r e p l a c e d by S.  Those f o r c e c o n s t a n t s which were  changed s l i g h t l y a r e shown i n T a b l e 43.  There were no a v a i l a b l e  o f t h e v a l u e s f o r t h e CS s t r e t c h i n g and CSC a n g l e bending  estimates  force constants,  - 187 and t h e v a l u e s f o r t h e CC s t r e t c h i n g  and CCC a n g l e bending f o r c e c o n s t a n t s  were used i n t h e i r p l a c e .  F i g . 45  In-plane i n t e r n a l coordinates of dibenzothiophene  T a b l e 43.  In-plane f o r c e constants of dibenzothiophene. Type H  H  H  F o r c e Constant  ccc  csc HCC  Value  = H e a) H = H X, n  0.91  H  0.94  H  n  E  H .= H . 0  H  0.51  A  = H y  0.73  0.50  IT  Force c o n s t a n t s not l i s t e d i n t h i s t a b l e were g i v e n t h e same v a l u e as t h o s e used f o r c a r b a z o l e i n T a b l e 11.  J.  Discussion The assignments o f t h e i n - p l a n e fundamental  thiophene-h  frequencies of dibenzo-  and -dg a r e g i v e n i n T a b l e 44 t o g e t h e r w i t h the r e s u l t s o f  t h e normal c o o r d i n a t e c a l c u l a t i o n .  The c a l c u l a t i o n was i n t h e n a t u r e o f  a preliminary t r i a l , assignments.  188 -  and t h e r e s u l t s were n o t used as a g u i d e i n making  No r e f i n e m e n t o f t h e f o r c e f i e l d was u n d e r t a k e n i n o r d e r t o  improve t h e agreement w i t h t h e observed f r e q u e n c i e s . The f a c t t h a t such an approximate c a l c u l a t i o n can g i v e r e a s o n a b l e agreement between the observed and c a l c u l a t e d f r e q u e n c i e s f o r b o t h d i b e n z o t h i o p h e n e - h  and -d o  the e s s e n t i a l c o r r e c t n e s s o f t h e f o r c e f i e l d . c o o r d i n a t e t r e a t m e n t s o f phenanthrene,  establishes o  A comparison o f t h e normal  c a r b a z o l e , and d i b e n z o t h i o p h e n e  s u p p o r t t h e o b s e r v a t i o n t h a t a s i m p l e v a l e n c e f o r c e f i e l d t r a n s f e r r e d among g e o m e t r i c a l l y s i m i l a r l a r g e o r g a n i c m o l e c u l e can g i v e an adequate of  t h e normal f r e q u e n c i e s .  account  I t can be f u r t h e r c o n c l u d e d t h a t t h e v a l u e s o f  t h e f o r c e c o n s t a n t s a s s o c i a t e d w i t h t h e CSC a n g l e bending and CS bond s t r e t c h i n g c o o r d i n a t e s i n dibenzothiophene are very s i m i l a r t o those f o r t h e CCC and a n g l e bending and CC bond s t r e t c h i n g c o o r d i n a t e s i n phenanthrene. A comparison o f t h e assignments o f t h e fundamental  frequencies of  d i b e n z o t h i o p h e n e w i t h c a r b a z o l e and f l u o r e n e i s p r e s e n t e d i n Appendix I I . A l t h o u g h t h e i n c o m p l e t e n e s s of t h e i n f r a r e d d a t a o f d i b e n z o t h i o p h e n e - d  has o  been i n d i c a t e d p r e v i o u s l y , i t i s mentioned assignment  a g a i n t o emphasize t h a t t h e  o f t h e d i b e n z o t h i o p h e n e fundamentals must be c o n s i d e r e d t e n t a t i v e .  33 According t o the T e l l e r - R e d l i c h product r u l e ,  the predicted r a t i o of the  product o f the frequencies f o r dibenzothiophene-d  compared w i t h d i b e n z o o  thiophene-h  i s 0.064 f o r t h e A. symmetry b l o c k . o  The r a t i o  calculated  I  from t h e observed f r e q u e n c i e s i s 0.17.  The poor agreement between t h e  observed and p r e d i c t e d r a t i o s need not n e c e s s a r i l y i n d i c a t e g r o s s d i s c r e p a n c i e s i n t h e a s s i g n m e n t s , b u t p o i n t s out t h e need f o r a more complete s e t of  data.  The r e s u l t s f o r t h e  and c a l c u l a t e d r a t i o  (0.18).  symmetry b l o c k a r e p r e d i c t e d r a t i o  (0.27)  The assignments f o r t h e A^ and B^ symmetry  b l o c k s a r e n o t complete so t h a t a p r o d u c t r u l e c a l c u l a t i o n i s n o t p o s s i b l e .  - 189 -  F i n a l l y , i t i s r a t h e r i n t e r e s t i n g t h a t an a l t e r n a t i v e e x p l a n a t i o n ( a p a r t from m i s a l i g n m e n t o f t h e c r y s t a l ) f o r t h e appearance  o f what i s  a p p a r e n t l y t h e same Raman a c t i v e l a t t i c e mode i n s e v e r a l p o l a r i z a t i o n s i s p o s s i b l e by t r e a t i n g t h e m o l e c u l e as a l i b r a t i n g harmonic o s c i l l a t o r .  This  s i m p l e t r e a t m e n t accounts r e a s o n a b l y w e l l f o r t h e e x p e r i m e n t a l o b s e r v a t i o n s .  T a b l e 44.  A  comparison of t h e observed and c a l c u l a t e d fundamentals f o r  dibenzothiophene  (DBT-h ) and 8  deuterodibenzothiophene  (DBT-dg).  Species  DBT-hg Observed  A  l  DBT-dg  Calculated  Observed  Calculated  .. .  3090  2309  2299  3055  3069  2284  2284  3025  3044  2271  2266  3000  3025  2225  2255  1593  1657  1568  1617  1557  1609  1521  1546  1475  1550  1417  1422  1421  1503  1320  1389  1318  1427  1283  1340  1233  1401  1201  1212  1203  1266  1175  1192  1133  1248  1125  1057  1068  1226  1059  924  1026  1136  911  902  934  1051  866  878  .85.4  808  828  779  712  743  664  705  494  505  484  494  403  386  390  372  215  223  199  209  - 190 -  Observed  B  2  Species A  DBT-" 8  DBT-hg  Species  d  Calculated  Observed  Calculated  2300  3117  3090  3055  3069  2284  .. .  3044  2267  3025  3025  2255  1514  1643  1478  1599  1462  1618  1446  1566  1442  1546  1380  1430  1353  1530  1335  1363  1314  1441  1286  1338  1268  1367  1160  1151  1156  1259  948  1089  1074  1204  854  972  1001  1139  833  921  966  1067  815  899  865  997  775  870  704  781  672  751  613  623  592  606  560  469  492  452  496  458  472  441  DBT-hg  DBT-d 156  2 287?  8  • • •  Species  DBT-h  B  940  r  o  DBT-d 8 845  251  895  762  385  859  720  645  770  622  746  744  561  724  421  424  366  226  217  138  128  Chapter 9 A Study o f Some E l e c t r o n i c S t a t e s o f D i b e n z o t h i o p h e n e .  A.  Introduction In t h e complex d i b e n z o t h i o p h e n e a b s o r p t i o n spectrum i n s o l u t i o n , t h e o  o  two systems a t 3260 A (f=0.0299)  a  n d 2870 A (f=0.0665)  almost  certainly  r e p r e s e n t s e p a r a t e t r a n s i t i o n s , b u t each o f t h e more c o m p l i c a t e d r e g i o n s o  o  b e g i n n i n g about 2675 A ( f = 0.222) and 2450 A ( f = 0.645) may r e p r e s e n t more t h a n a s i n g l e t r a n s i t i o n .  P l a t t ^ suggested t h a t t h e assignments o f 1  t h e s e bands, i n o r d e r o f d e c r e a s i n g w a v e l e n g t h , a r e s h o r t , l o n g , l o n g , and s h o r t a x i s p o l a r i z e d , r e s p e c t i v e l y , by comparison w i t h t h e assignments f o r phenanthrene.  o  o  The assignment o f t h e 3260 A and 2870 A systems agrees 89 w i t h S i e g e l and J u d e i k i s ' r e s u l t s o b t a i n e d from broad-band magnetophotos e l e e t i o n e x p e r i m e n t s on d i b e n z o t h i o p h e n e i n d i e t h y l e t h e r s o l u t i o n a t ' 123 77°K, and i s s u p p o r t e d by D o r r ' s p h o t o s e l e c t i o n e x p e r i m e n t s . In t h i s c h a p t e r , t h e work on d i b e n z o t h i o p h e n e i s c o n f i n e d t o a s s i g n i n g t h e symmetry o f t h e l o w e s t - e n e r g y s i n g l e t s t a t e , t o i n v e s t i g a t i n g t h e e x c i t e d s t a t e v i b r a t i o n a l s t r u c t u r e from t h e a b s o r p t i o n spectrum, and t o s t u d y i n g the ground s t a t e v i b r a t i o n a l s t r u c t u r e from f l u o r e s c e n c e and phosphorescence spectra. B.  A b s o r p t i o n Spectrum M i c r o d e n s i t o m e t e r t r a c i n g s o f dibenzothiophene a b s o r p t i o n s p e c t r a i n  n-heptane  and f l u o r e n e m a t r i c e s a r e r e p r o d u c e d i n F i g . 46, and an a n a l y s i s  -192  30000 46  -  30 500  31OOO cm-'  A b s o r p t i o n ' s p e c t r a o f d i b e n z o t h i o p h e n e i n n-heptane (above) and i n fluorene  (below) a t about 15°K. The energy s c a l e r e f e r s o n l y  to dibenzothiophene i n fluorene..  - 193 -  of the v i b r a t i o n a l  s t r u c t u r e i n hexamethylbenzene and n-heptane i s s e t  out i n T a b l e 4 5 , The v i b r a t i o n a l  s t r u c t u r e of dibenzothiophene i n fluorene  m a t r i x i s b r o a d even a t t h e l o w e s t t e m p e r a t u r e s a t t a i n a b l e so t h a t v i b r o n i c symmetry assignments a r e not p o s s i b l e .  I n n-heptane, t h e most  intense  l i n e s i n t h e l e a d i n g m u l t i p l e t were l o c a t e d as resonance l i n e s a t 30 205, 30 341,  Table  30 364 and 30 423 cm .  45.  1  F o r s i m p l i c i t y and c l a r i t y , t h e a n a l y s i s  A b s o r p t i o n s p e c t r a o f d i b e n z o t h i o p h e n e i n n-heptane and hexamethylbenzene (HMB) a t about 15°K.  HMB  Int  30 760  s  30-423  s  origin  215  m  213  s  213, F  267  w  267  w  ?  396  w  405  w  477  m  n-heptane  Int  Remarks  a  396,F 402  s  402,F  420  m  2 x 213 - 6  485  s  485,F  681  w  ?  689  m  693  ms  693, F  870  m  881  mw  402 + 485 - 6  891  mw  891, F  1001  ms  1001,F  995  mw  1042  w  1083  w  1087  m  1087,F  1215  vw  1208  m  1208,F  1257  vw  1253  w  ?  1320  mw  1308  m  1308,F  1417  w  ?  1432  w  1432,F  1486  mw  1486,F  1439  w  - 194 -  HMB  Int  n-heptane  Int  Remarks  1521  mw  1521,F; 213 + 1308  .1569  mw  1569,F  1648  w  ?  1729  w  1  1790  w  485 + 1308 - 3  1998  w  693 + 1308 - 3  F i n d i c a t e s t h a t t h e i n t e r v a l may correspond fundamental.  t o an e x c i t e d s t a t e  i n T a b l e 4 5 i s based on those i n t e r v a l s a s s o c i a t e d w i t h t h e p r i n c i p a l o r i g i n a t 30 423 cm . 1  Although  benzene m a t r i x i s c o m p l e t e l y  t h e a b s o r p t i o n spectrum i n hexamethyl-  d e p o l a r i z e d , t h e bands axe q u i t e s h a r p , and  are i n c l u d e d i n T a b l e 45 f o r comparison w i t h t h e n-heptane a n a l y s i s .  1  C.  Fluorescence  Spectra  The f l u o r e s c e n c e s p e c t r a i n f l u o r e n e and n-heptane m a t r i c e s , and t h e c r y s t a l a r e shown i n F i g . 47 and t h e v i b r a t i o n a l i n t e r v a l s a r e g i v e n i n T a b l e 46.  The assignments o f t h e f l u o r e s c e n c e bands i n n-heptane are based  on t h e i n t e r v a l s a s s o c i a t e d w i t h t h e p r i n c i p a l o r i g i n a t 30 423 cm . 1  The  f l u o r e s c e n c e o r i g i n i n t h e f l u o r e n e m a t r i x i s w e l l p o l a r i z e d along t h e b - a x i s , but t h e v i b r o n i c bands i n t h e r e s t of t h e spectrum 'are e s s e n t i a l l y d e p o l a r i z e d , and a r e t o o broad t o be measured p r e c i s e l y enough f o r use i n a vibrational analysis. matrix.  D i b e n z o t h i o p h e n e was a l s o s t u d i e d i n a b i p h e n y l  The r e s u l t s , a p a r t from a s o l v e n t s h i f t , a r e s i m i l a r t o f l u o r e n e  i n t h a t t h e a b s o r p t i o n and f l u o r e s c e n c e are a l s o b r o a d .  The  crystal  f l u o r e s e n c e i s q u i t e sharp w i t h an average band w i d t h o f 10 cm \  and has most  - 195 -  27500  28 0 0 0  28 500  29 OOO  29 5 0 0  30 000  in rO  | 27 500  28 OOO  i  |  28 OOO  28 500  |  |  28 500  29 OOO  29 5 0 0  29OOO  29500  WAVENUMBER 47  30000  | 30  OOO  30 5 0 0  (cm-')  D i b e n z o t h i o p h e n e f l u o r e s c e n c e s p e c t r a i n (a) a f l u o r e n e m a t r i x , (b) the c r y s t a l , and (c) an n-heptane  s o l u t i o n at about  15"K.  - 196 of i t s i n t e n s i t y along the s - a x i s .  T a b l e 46.  Dibenzothiophene fluorescence i n a f l u o r e n e m a t r i x , the c r y s t a l , and an n-heptane s o l u t i o n a t about 15°K.  Fluorene //b  matrix //c  Int  30 048  Crystal //s  Int.  29 923  38  w  74  m  16  w  42  s  63  s '  79  w  91  m  101  w  ms  138  w  210  ms  219  s  258  ms  310  vw  354  vw  409  w  m  305  m  321  Remarks reabsorbed  214  ms  214,A^  404  vw  404,A  ms 351  378  ms m  416  m w  446 468  s  567  ms 609  632  :  -  w  500  499  m  498  s  498,Aj  707  w  705  m  705,A  717  m  214 + 498 + 5  w m  665 706  Int.  30 423  138  284  n-heptane  w m  :  - 197 -  Fluorene matrix //b  //c 738  756  Int.  Crystal //s  I n t . n-heptane  Int.  Remarks  vw m  796  vw  850  vw  814  vw 850  vw  850^  997  vw  2 x 498 + 1  vw  875  1023  w  1027  mw  1023  m  1023^  1078  w  1079  w  1079  w  1079  1132  w  1132  w  1132  mw  1132,A  1154  vw  1199  vw  1199;  1226  vw  1226  1240  w  1240  1310  vs  1310,A  1373  vw  1373  1397  vw  1397  1415  vw  2 x 705 + 5  1164  w  1170  vw  1174  vw  1204  vw  1205  vw  1239  vw  1311  s  1349  m  1237  w  1269  vw  1287  vw  1315  vs  m  1403  x  498 +  :  1474  w  1477  mw  1479  w  1479  1524  w  1528  mw  1526  m  214 + 1310  1569  vw  1588  vw  1591  vw  1591  1602  s  1603  s  1603,A  1602  ms 1636  1659  w w  1692  w  1  - 198 -  Crystal  Fluorene matrix Int.  //b  Int.  1821  w  n-heptane  Int.  Remarks  w  1728 1758  w  1769  vw  1811  vw 1816  vw  1842  vw  m  498 + 1310 + 1  2103  w  498 + 1603 + 2  2331  vw  1023 + 1310 + 2  2621  w  2 x 1310 + 1  1809  vw  1904 1942  vw  2100  vw  2190  vw  D-  //s  Phosphorescence  •  2098  vw  2297  vw  2335  vw  2376  vw  2437  vw  2625  w  Spectra  M i c r o d e n s i t o m e t e r t r a c i n g s o f t h e phosphorescence s p e c t r a o f d i b e n z o thiophene i n n-heptane  and hexamethylbenzene m a t r i c e s , and from t h e c r y s t a l  at about 15°K a r e r e p r o d u c e d i n F i g . 48, and t h e v i b r a t i o n a l  intervals  t o g e t h e r w i t h t h e i r assignments based on t h e c r y s t a l spectrum a r e g i v e n i n T a b l e 47.  With c o r r o b o r a t i o n from i n f r a r e d  44, t h e symmetry assignments o f t h e v i b r o n i c t i o n t h a t o n l y A^ or/  and Raman d a t a l i s t e d i n T a b l e bands were made on the assump-  fundamentals have a p p r e c i a b l e i n t e n s i t y  phosphorescence spectrum,.  i n the  The phosphorescence spectrum i n n-heptane i s  p a r t i c u l a r l y complex; t h e components o f t h e l e a d i n g m u l t i p l e t  are located  - 199 -  F i g . 48  Phosphorescence s p e c t r a o f d i b e n z o t h i o p h e n e i n [a) hexainethylbenzene, 15°K.  (b) t h e c r y s t a l , and (c) n-heptane s o l u t i o n at about .  - 200 at 24 476, 24 417, 24 433, 24 395, 24 367, 24 344, 24 327, and 24 297 cm" . 1  Only t h e bands a s s o c i a t e d w i t h t h e p r i n c i p a l  o r i g i n a t 24 417 cm  1  are  i n c l u d e d i n T a b l e 47.  T a b l e 47.  Phosphorescence s p e c t r a o f d i b e n z o t h i o p h e n e i n n-heptane hexamethylbenzene (HMB) m a t r i x and  n-heptane  Int.  HMB  24 417  vs  24 096  210  m  221  m  417-  ms  429  ms  499  560  632 707  740  s  s  m  s  s  Int.  223  413  495  556  628  707  734  vs  ms  ms  ms  s  Crystal  Int  24 292  vs  16  s  40  ms  65  w  84  vw  solution,  c r y s t a l a t about 15°K.  Remarks origin  110  m  145  m  180  m  216  s  237  m  ' 1 237?  254  w  216  425  m  425,A  438  m  2 x 216 + 6  498  s  498,A  514  •w  543  vw  498 + 4 0 + 5  564  s  564,A  579  w  564  +16-1  607  vw  564  +40+3  643  vw  216 + 4 2 5 - 2  706  s  706,A  725  mw  706 + 16 f 3  746  m  746?  2 1 6  A  +40-2  -  x  1  498 .+ 16  1  vw  s  ms  1  0  - 201 -  -heptane 768  851  934  Int. s  vvs  s  1007  w  1024  w  1061  vw  1072  mw  HMB  Int.  767  m  779  m  849 870  931  1028  mw  Remarks  Int.  771  m  771?  vvs  855  vvs  855 A  m  875  m  855  894  m  855 + 4 0 - 1  920  m  216 + 706 - 2  937  s  937,A  954  w  937  1003  w  1003,A  1026  ms  1026,A^  1038  w  1026 + 1 6 - 4  ms  w  1053 w  1134  Crystal  3  1  +16+4  x  +16+2 1  (212 + 851 - 2) 1072  m  1070  ms  1070,A  1093  vs  1087  w  1070 + 1 6 + 1  1118  vw  1118  m  1118?  1136  m  1133  ms  1133^  1153  ms  1153,k ; 1133 + 1 6 + 4  1171  ms  1133  1201  m  1201,k  x  1234  m  1234,A  :  +40-2?  1204  w  1227  w.  1267  w  1261  w  1268  w  564 + 706 - 2;498 + 771  1293  w  1290  vw  1285  w  216 + 1070 - 1  1315  w  1316  s  1316,A  1333  w  1316 + .16 + 1  1200  w  :  x  1349  m  1345  ms  1352  s  1352,A  1416  w  1412  w  1412  w  2 x 706  1431  vw  1441  w  1429  w  2 x 706 + 6 + 1  1450  w  216 + 1234  1476 (1498)?  1  w  1467  m  1476  m  1476,A  w  1491  m  1494  w  2 x 746 + 2  1527  m  498 + 1026 + 3  :  1556  m  1554  ms  1559  s  1 5 5 9 ^ ? ; 706 + 855 - 2  1582  m  1585  w  1581  w  1581,A, 3  1  - 202 -  n-heptane 1602  Int.  HMB  Int. Crystal  Int.  vs  1612  vs  1601  vs  1618  s  1601  1640  m  1601 + 40 - 1  1693  w  216 + 1476 + 1  1710  w  2 x 855  1694  vw  Remarks 1601 A 3  1 16 + 1  +  1718  m  (707 + 1007 + 4;  1729  w  (707  1824  mw 1839  1878  1925  m  1876  mw mw  1024 - 2;  1744  w  425 + 1316 + 3  1773  w  425 + 1352 - 4  1792  w  771 + 1026 - 5  1816  m  216 + 1601 - 1  1834  w  216 + 1601 + 16  1855  w  216  1879  m  855 + 1026 - 2  1910  V/  706 + 1201 + 3  1601 + 40  w 1965?  1984  m  1988  mw  1988  mw  855 + 1133  2035  w  2020  mw  2021  mw  425 + 1601 - 5  2056  w  2 x 1026 + 4  2097  m  498 + 1601 _ 2  2139  vw  2 x 1070 ,+ 1  m  564  2103  m  2101  mw  2164  ms  2166  m  2167  2187  m  2189  mw  2178  2271  w  2272  vw  2262  w  2 x 1133 - 4  2311  mw  2316  mw  2305  w  706 + 1601 - 2  2342  mw  2339  w  1026  2385  w  2382  w  10261 -r• 1352 + 4  2426  w  2417  w  706 + 2 x 855 +  2462  m  2454  m  855 + 160.1 - 2  2482 •  w  2472  vw  855 + 1601 + 16  2490 .  vw  855  2536  w  937 + 1601 - 2  2456  2538  ms  m  2543  w  1601 + 2  i  • 1316  +  1601 + 40  - 203 -  n-heptane  Int.  HMB  w  2670  w  1070 -r 1601 - 1  2730  vw  2733  vw  1133  Hr  2750  vw  2755  vw;  1153  + 1601 + 1  2813  WW  2802  VW  1201 -i- 1601  2834  vw  1234 + 1601 - 1  2877  vw  706 + 855 + 1316  2911  w  1316 + 1601  2952  w  1352 + 1601  3124  vw  1527 + 1601 - 4?  mw  2684  2737  mw  mw  Remarks 1026 + 1601 - 2  2676  2953  Int. w  mw  w  Crystal 2625  2627  2808  Int.  2957  vw  1601 - 1  3160  mw  3168  vw  3159  vw  706 + 855 '+ 1601 - 3  3205  m  3226  w  3200  w  2 x 1601 - 2  3414  vw  216 + 2 x 1601 - 4  3487  vw  855 '+ 1026 + 1601 + 6  3773  vw  564 + 2 x 1602 + 7 .  vw  3448 3479  w  3766  w  3775  VW  3898 ' vw  E.  3978  w  4057  w  vw  4073  3983  vw  771 + 2 x 1601 + 10  4058  vw  855 + 2 x 1601 + 1  Discussion  o The p u r e e l e c t r o n i c  o r i g i n o f t h e weak a b s o r p t i o n system at 3260 A  of dibenzothiophene i n a fluorene matrix i s p o l a r i z e d ( F i g . 4 7 ) , and i s a s s i g n e d as an ^A^ Piatt's p r e d i c t i o n , a n d Siegel  —  along the b-axis  *A^ t r a n s i t i o n i n agreement w i t h  and J u d e i k i s '  experimental  result.^  The r e a b s o r p t i o n o f t h e f l u o r e s c e n c e o r i g i n so c h a r a c t e r i s t i c o f medium s t r e n g t h and s t r o n g t r a n s i t i o n s fluorescence polarized  i s c l e a r l y d i s p l a y e d i n F i g . 47.  along t h e . r - a x i s of the c r y s t a l probably  The  gives a  f a i r l y a c c u r a t e i n d i c a t i o n o f t h e i n t e n s i t y o f t h e o r i g i n band r e l a t i v e t o  - 204  -  the r e s t o f the bands i n the spectrum. Apparently, the breadth  o f b o t h the a b s o r p t i o n and f l u o r e s c e n c e .  spectrum o f d i b e n z o t h i o p h e n e i n f l u o r e n e and b i p h e n y l i s a m a n i f e s t a t i o n o f guest-host  i n t e r a c t i o n s which at p r e s e n t have no e x p l a n a t i o n .  Clearly,  t h e i n t e r a c t i o n depends on the m a t r i x because the a b s o r p t i o n and  fluores-  cence o b s e r v e d i n the c r y s t a l and n-heptane i s s h a r p . Since only w e l l as  TT-TT*  t r a n s i t i o n s a r e p o s s i b l e i n f l u o r e n e and n-n*  t r a n s i t i o n s may  TT-TT*  c o n c l u s i o n may  be p o s s i b l e i n d i b e n z o t h i o p h e n e ,  be drawn from a comparison o f t h e f l u o r e s c e n c e  phosphorescence s p e c t r a o f t h e s e compounds i n n-heptane. support  the g e n e r a l  transitions:  TT-TT*  n a t u r e o f the l o w e s t - e n e r g y  Two  an  as important  and observations  s i n g l e t and  triplet  ( i ) b o t h the f l u o r e s c e n c e and phosphorescence s p e c t r a o f  f l u o r e n e i n n-heptane F i g . 4 7 and 48 show t h a t the g e n e r a l f e a t u r e s o f the v i b r a t i o n a l s t r u c t u r e a r e s i m i l a r , and  ( i i ) i n a l c o h o l , the d i b e n z o t h i o p h e n e  s p e c t r a do not show the b l u e s h i f t t h a t i s c h a r a c t e r i s t i c o f an transition. ^  T h e o r e t i c a l studies of thiophene *'  1 2  and  12  -TT*  N  dibenzothiophene *^ 12  have been concerned w i t h the c o n t r i b u t i o n o f the s u l p h u r d o r b i t a l s e l e c t r o n i c MO  i n TT  c a l c u l a t i o n s , but t h e r e s u l t s o f t h e s e c a l c u l a t i o n s are i n -  c o n c l u s i v e s i n c e d o r b i t a l p a r t i c i p a t i o n has not been demonstrated. The  d e c r e a s e d f l u o r e s c e n c e y i e l d and i n c r e a s e d phosphorescence y i e l d  o f dibenzothiophene compared w i t h f l u o r e n e i s i n a c c o r d w i t h the S*-T* energy gap  (9400 c m  -1  i n f l u o r e n e and 6000 cm"  1  smaller  i n dibenzothiophene) 123  and the i n c r e a s e d s p i n - o r b i t c o u p l i n g due phosphorescence from the c r y s t a l was  t o the s u l p h u r atom.  Although  observed at 77°K, a t e m p e r a t u r e dependent  s t u d y i s r e q u i r e d t o d e t e r m i n e whether t h e l u m i n e s c e n c e i s from the c r y s t a l b u l k or from d e f e c t s i t e s i n the l a t t i c e . n o r m a l l y o b s e r v e d from p e r f e c t o r g a n i c m o l e c u l a r  Phosphorescence i s not c r y s t a l s because d u r i n g  the  - 205 -  l o n g l i f e t i m e o f the t r i p l e t e x c i t o n t h e r e i s a h i g h p r o b a b i l i t y t h a t s e v e r a l 19 e x c i t o n s i n the c r y s t a l may  i n t e r a c t and a n n i h i l a t e s i m u l t a n e o u s l y .  The v i b r a t i o n a l a n a l y s i s of the phosphorescence s p e c t r a i s s t r a i g h t f o r w a r d , and no s p e c i a l f e a t u r e s are n o t e d .  There a r e no  a p a r t from the o v e r t o n e o f the 1600  bond s t r e t c h i n g v i b r a t i o n ,  t h a t the t r i p l e t state.  The  cm  1  C-C  progressions, so  s t a t e geometry must be v e r y c l o s e t o t h a t o f the ground  f l u o r e s c e n c e a n a l y s i s , a l t h o u g h not v e r y e x t e n s i v e , i s  c h a r a c t e r i s t i c o f a s i n g l e t t r a n s i t i o n i n an a r o m a t i c m o l e c u l e t h a t undergone v e r y l i t t l e shape change.  has  C h a p t e r 10 A Study o f B i p h e n y l C r y s t a l Phosphorescence by  A.  Induced  Impurities  Introduction Very few examples o f phosphorescence from c a r e f u l l y p u r i f i e d  single  c r y s t a l s o f a r o m a t i c compounds a r e known, and the r e a s o n f o r t h i s l i e s i n 127 the  now w e l l - i n v e s t i g a t e d phenomenon o f t r i p l e t - t r i p l e t  annihilation.  A l t h o u g h the mechanism o f t h e energy t r a n s f e r i s not c o m p l e t e l y u n d e r s t o o d , the  e s s e n t i a l s t e p s can be d e s c r i b e d a c c o r d i n g t o a s i m p l e scheme. T + T  y  S* + S (10.1)  S  —y  S + hv  D u r i n g t h e r e l a t i v e l y long l i f e t i m e o f the t r i p l e t  s t a t e i n the c r y s t a l *  two t r i p l e t e x c i t o n s (T) i n t e r a c t t o c r e a t e a s i n g l e t e x c i t o n (S ) wliich may  s u b s e q u e n t l y decay t o the ground s t a t e (S) by a r a d i a t i v e p r o c e s s .  The r e s u l t i n g e m i s s i o n , which i s c a l l e d d e l a y e d f l u o r e s c e n c e , i s s p e c t r a l l y i d e n t i c a l t o t h e normal S'"' S f l u o r e s c e n c e , but e x h i b i t s a l i f e t i m e o f the -y  o r d e r o f m i l l i s e c o n d s t o seconds.  Weak e x c i t o n phosphorescence has been  r e p o r t e d f o r b e n z o p h e n o n e , ^ some p - d i h a l o g e n a t e d b e n z e n e s , ^ 1  1 2  and  130-132 anthracene c r y s t a l s . 'When the e m i s s i o n o r i g i n a t e s a t a t r a p , u s u a l l y t a k e n t o be some ( u n s p e c i f i e d ) l a t t i c e i m p e r f e c t i o n , t h e phosphorescence 132 133 i n t e n s i f i e s at low t e m p e r a t u r e s . " '  The purpose o f the f o l l o w i n g work  - 207 i s t o show t h a t phosphorescence may  be induced  from the m a t r i x by  i m p u r i t i e s t h a t themselves cannot a c t as a c c e p t o r s  B.  Carbazole  residual  o f the t r i p l e t  energy.  i n Biphenyl  In a c r y s t a l o f b i p h e n y l doped w i t h c a r b a z o l e , t h e a b s o r p t i o n  and  f l u o r e s c e n c e s p e c t r a are c h a r a c t e r i s t i c o f c a r b a z o l e s i n c e the v i b r a t i o n a l analyses  (see Appendix I) a r e e s s e n t i a l l y i d e n t i c a l t o those a l r e a d y  w i t h f l u o r e n e as m a t r i x .  F o l l o w i n g arguments p r e s e n t e d  by  given  Hochstrasser  82 and S m a l l ,  c a r b a z o l e may  lattice.  occupy s e v e r a l d i f f e r e n t s i t e s i n the  For example, i n a bc_' f a c e , two prominent o r i g i n bands are  b o t h i n f l u o r e s c e n c e and a b s o r p t i o n at 29 672 t h i r d weaker l i n e at 29 678  cm  and  29 698 cm  1  Complete s p e c t r a are b u i l t on each l i n e .  ( 2 0 l ) secondary c l e a v a g e p l a n e , o n l y two o r i g i n s a t 29 678  29 698  cm  1  are observed.  understood, although  i t may  s e c t i o n s were p r e p a r e d  active  as w e l l as a  In the  T h i s v a r i a t i o n i n i n t e n s i t y was  rioted  and but  have been r e l a t e d t o the f a c t t h a t the  by s u r f a c e g r i n d i n g .  The  not  be'  l i n e s were about 5 cm  wide a t a t e m p e r a t u r e o f about 10-15°K c o r r e s p o n d i n g strong  biphenyl  1  to conditions of  irradiation.  Pure b i p h e n y l c r y s t a l s d i d not phosphoresce even at the lowest t u r e s r e a c h e d (about 6°K).  However, when b i p h e n y l was  an i n t e n s e , b l u e phosphorescence was  e a s i l y recorded.  doped w i t h  carbazole  A s t u d y o f the  v i b r a t i o n a l i n t e r v a l s and o f the r e l a t i v e l i n e s t r e n g t h s shows t h a t e m i t t i n g s p e c i e s i s b i p h e n y l and not c a r b a z o l e . a n a l y s i s are shown on the d e n s i t o m e t e r and t h i s may  tempera-  the  The main f e a t u r e s o f the  t r a c i n g o f the spectrum i n F i g . 49,  be compared w i t h the phosphorescence spectrum o f b i p h e n y l i n  paraffin s o l v e n t s .  1 0 9  '  1 1 0  The  spectrum d i s p l a y s the same type o f m u l t i p l e t  s t r u c t u r e t h a t i s e v i d e n t i n the f l u o r e s c e n c e and a b s o r p t i o n s p e c t r a o f  - 208 -  21 O O O  21500  2 2 OOO  22 5 0 0  23  OOO  Wavenumber (cm ) -1  F i g . 49  Phosphorescence s p e c t r a of b i p h e n y l c r y s t a l s doped w i t h (a) c a r b a z o l e at about 6°K,  (b) c a r b a z o l e at 17°K  showing a second  /  t r a p coming i n t o prominence, (c.) d i b e n z o t h i o p h e n e - h g at about 6°K, and (d) d i b e r . z o t h i o p h e n e - d  R  at about  6°K.  - 209  carbazole  -  at s h o r t e r wavelengths (see Appendix I ] .  two phosphorescence o r i g i n bands at 22 939  and  be'  22 970 cm  ( 2 0 l ) s e c t i o n s s t u d i e d , t h e r e are t h r e e at 22 934, These o b s e r v a t i o n s  The  22 960,  s e c t i o n s show and i n the and  22 985  t o the i m p u r i t y s i t e so as t o c r e a t e c o r r e s p o n d i n g l o c a l t r i p l e t .. . band s t r u c t u r e . i s about 1700  cm  -1  sub-  adjacent  energy minima i n the  A l t h o u g h the t r i p l e t l e v e l of  above the b i p h e n y l t r i p l e t band, t h e r e i s no  1  cm .  i n d i c a t e t h a t the s e v e r a l ways t h a t c a r b a z o l e may  s t i t u t e i n the host p e r t u r b the b i p h e n y l m o l e c u l e s o f the l a t t i c e  four  carbazole evidence  from t h e t e m p e r a t u r e dependence s t u d i e s t o suggest t h a t t h e minima represent  m e t a s t a b l e l e v e l s ; on the c o n t r a r y , the s t u d i e s s u b s t a n t i a t e the  f a c t t h a t the minima are energy t r a p s below the band. so f a r are  o f one  ture i s raised.  The  t r a p s mentioned  t y p e s i n c e they show a s i m i l a r b e h a v i o u r as the tempera-  The  s e t o f o r i g i n bands grow weaker, broaden, and  rapidly  merge i n t o a s i n g l e l i n e t h a t appears t o s h i f t s l o w l y t o lower wavelengths presumably because the h i g h e r energy t r a p s are the f i r s t t o empty i n t o band. These were t r e a t e d as though degenerate and  the  are r e f e r r e d t o c o l l e c t i v e l y  as t r a p s o f t y p e 1 (J ~). A second type o f t r a p (T^) was  l o c a t e d by the appearance of a n o t h e r  b i p h e n y l phosphorescence o r i g i n at 22 886 origin  (see F i g . 49).  These were d e t e c t e d  cm  1  t o t h e red o f the  first  o n l y at h i g h e r t e m p e r a t u r e s where  t r a p s o f t y p e 2 became more a c t i v e a t the expense o f t h o s e o f t y p e 1. probably  occurs  t h r o u g h the p r e s e n c e e i t h e r of a second u n s u s p e c t e d  w i t h l e v e l s above the c o r r e s p o n d i n g molecules i n close proximity.  The  ones of b i p h e n y l , or o f two  7  impurity  carbazole  o b s e r v a t i o n o f deeper t r a p s t h a t show an  analogous b e h a v i o u r i n b i p h e n y l doped w i t h d i b e n z o t h i o p h e n e suggests t h a t the l a t t e r e x p l a n a t i o n  i s correct.  - 210 -  The k i n e t i c s o f t h e t r i p l e t - t r i p l e t  a n n i h i l a t i o n process  i n a mixed  c r y s t a l system i n v o l v i n g a number o f t r a p s cannot be t r e a t e d e a s i l y .  The  f o l l o w i n g scheme shows o n l y t h e more s i g n i f i c a n t s t e p s a f t e r t h e e x c i t a t i o n energy has t r a n s f e r r e d t o a guest  molecule. S  N o n - r a d i a t i v e quenching:  -> S *  Guest f l u o r e s c e n c e :  l  k  l  k  2  k  3  k  4 * 4  *  -> S + h v r  S  k  c  *  Intersystem crossing:  s  Intersystem crossing:  -  T  l  *  s  N o n - r a d i a t i v e quenching a t t r a p T : • T Phosphorescence from t r a p T • 1  T  1  S + hv  1  N o n - r a d i a t i v e quenching at t r a p T 2 : Phosphorescence from t r a p T' • 2 Tj a n n i h i l a t i n g at s i t e  l  + T  T j a n n i h i l a t i n g a t s i t e T '•  T  l  +  T^:  p  k  -+ S  2  5  K  S + hv  * p  5  K  * T  T^ a n n i h i l a t i n g a t s i t e  T  T 2  T^: 2  -* S  T  2  ->- s + s s* + s  l T  2 T  +  K  l  K  2  K  3  *  -> s  2  + s  The s u b s c r i p t s F and P denote f l u o r e s c e n c e and phosphorescence r e s p e c t i v e l y . The u n s t a r r e d c o n s t a n t s r e p r e s e n t n o n - r a d i a t i v e p r o c e s s e s , and t h e s t a r r e d constants r e f e r to r a d i a t i v e  processes.  The v a r i a t i o n o f t h e i n t e n s i t y o f t h e phosphorescence from (I  and I l  p  p  and T  2  , r e s p e c t i v e l y ) and t h e d e l a y e d f l u o r e s c e n c e from c a r b a z o l e 2'  (I „) w i t h t e m p e r a t u r e i s shown i n F i g . 50. n  The maximum i n I  t h a t t r a p s o f one type were emptying i n t o t h e band, w i t h a n n i h i l a t i o n subsequently  occurring.  indicated  triplet-triplet  The emptying t r a p was i d e n t i f i e d by  observing a r a p i d decrease i n the corresponding  I , i n t h i s case I  .  The  P recombination  p r o c e s s may be d e s c r i b e d  1 2  ' ' ' i n terms o f t h e c o n c e n t r a t i o n s  * of s i n g l e t e x c i t e d carbazole molecules  [ S ] and o f t h e o c c u p i e d t r a p s o f  t y p e s 1 and 2 [T ] and [T^], r e s p e c t i v e l y , by t h e e q u a t i o n  4I§J-  O  = K  l [ T l  ]  2 +  K [ 2  T l  ][T ] 2  +  K [T ] 3  2  2  (10.2)  - K [S*] 4  Ip  CO t  1600-  D  y  CC  140  F i g . 50 Temperature v a r i a t i o n of t h e i n t e n s i t y o f t h e phosphorescence ( I and 1 ^ ) and  <  cc t  CD  cc < ^_  n  120  of t h e d e l a y e d f l u o r e s c e n c e  lOO  b  CO  2 LU IZ  V2  Pi  from a b i p h e n y l so  c r y s t a l doped  with•carbazole.  o-t-  lO  15  T E M P E R A T U R E  20  £5  ° K  The t e m p e r a t u r e dependent a n n i h i l a t i o n r a t e c o n s t a n t s  and -X.  involve  t h e s m a l l e r t r a p depth and K , t h e l a r g e r t r a p d e p t h , e x p o n e n t i a l l y . r a t e constant K k, .  I DF'  i s t h e sum of, the l e s s temperature-dependent  terms  The and  The f i r s t term on t h e r i g h t hand s i d e o f t h e r a t e e q u a t i o n r e f e r s t o  the a n n i h i l a t i o n o f T. a t a n o t h e r T  s i t e , t h e second term t o T, a n n i h i l a t i n g  - 212 at T , and t h e t h i r d t o 1'^ a n n i h i l a t i n g a t a n o t h e r T' . 2  might be e x p e c t e d t o dominate at low t e m p e r a t u r e where  Each of t h e s e terms  i n d i f f e r e n t temperature r e g i o n s .  In p a r t i c u l a r  was observed t o be v e r y s m a l l t h e f i r s t s h o u l d  be the i m p o r t a n t s e c o n d - o r d e r term.  Then the s t a t i o n a r y - s t a t e a p p r o x i m a t i o n  * may be a p p l i e d t o [S ] t o g i v e t h e r e l a t i o n log  Cine/  Ub  1  p  2  )  constant (-AE /kT)  =  1  1  J  (10.3)  The s l o p e o f t h e l i n e a r p o r t i o n o f such a p l o t y i e l d e d a d e p t h f o r t h e s e t of s h a l l o w t r a p s o f about 250 cm o ~i  *r  (see F i g . 5 1 ) .  1  T h i s may be an o v e r - e s t i m a t e 1  —  l/T F i g . 51  P l o t s o f l o g ( i n t e n s i t y r a t i o s ) v s . 1/T f o r the c a r b a z o l e / b i p h e n y l system.  - 213 1^  o f t h e t r a p depth s i n c e t h e r e may be s i g n i f i c a n t c o n t r i b u t i o n s t o a r i s i n g from o t h e r p r o c e s s e s  i n the higher temperature r e g i o n .  I n any  event t h e p e r c e n t a g e e r r o r (^20%) i n t h i s energy i s l a r g e s i n c e i t was e s t i m a t e d o v e r a s m a l l t e m p e r a t u r e range u s i n g a r e l a t i v e l y crude thermometer. The mean phosphorescence energy from t h e s e t o f t r a p s T^ i s 22 960 cm . 1  I f t h i s v a l u e f o r t h e t r a p depth i s a c c e p t e d ,  the corresponding  o f t h e energy gap t o t h e t r i p l e t band i s about 23 210 cm  estimate  This  estimate  assumes t h a t any p e r t u r b a t i o n i n t h e ground s t a t e o f b i p h e n y l i s s m a l l compared w i t h those i n t h e t r i p l e t Hirota  135  I n a more d i r e c t measurement,  found t h e band gap a t 78°K t o be about 23 200 cm  r e s u l t suggests  -1  .  This  t h a t t h e n e t r e p u l s i v e e f f e c t on t h e ground e l e c t r o n i c  s t a t e o f a biphenyl molecule lattice  state.  caused by t h e i n s e r t i o n i n t o an a d j a c e n t  s i t e of a carbazole molecule  (having a d i f f e r e n t shape) must be  appropriately small. 2 2 P l o t s formed by r e p l a c i n g I by I I o r I l l 2 2 above d i d n o t y i e l d s t r a i g h t l i n e s . p  P  P  i n the s i m p l i f i e d  expression  p  Other ways t h a t t h e t r i p l e t band may become d i s t o r t e d may be p o s t u l a t e d . For example, i f t h e s o l u t e c o n c e n t r a t i o n were made h i g h enough, t h e t r a p s c o u l d become connected t h e r m a l l y t h r o u g h triplet  e x c i t o n band d i r e c t l y .  c l u s t e r i n g without i n v o l v i n g the  C l u s t e r i n g s h o u l d be u n i m p o r t a n t i n our -4 -3  samples s i n c e t h e nominal c o n c e n t r a t i o n s ranged from 5 x 10  t o 4 x 10  M/M  and t h e a c t u a l c o n c e n t r a t i o n s may w e l l have been l e s s . C.  Dibenzothiophene i n Biphenyl The  same g e n e r a l b e h a v i o u r  dibenzothiophene.  was observed  when b i p h e n y l was doped w i t h  I n t h i s c a s e , t h e b i p h e n y l phosphorescence bands (as w e l l  as t h e dibenzothiophene  f l u o r e s c e n c e and a b s o r p t i o n bands) a r e u n u s u a l l y broad  - 214 -  -  (about 250 cm *) and no m u l t i p l e t s c o u l d be found (see F i g . 4 9 ) .  Possibly  d i b e n z o t h i o p h e n e o c c u p i e s a l a r g e number o f d i f f e r e n t s i t e s i n t h e h o s t lattice,  o r even some form o f h i n d e r e d r o t a t i o n may o c c u r i f two b i p h e n y l  molecules are replaced. The change o f s o l u t e from c a r b a z o l e t o d i b e n z o t h i o p h e n e caused t h e h i g h e s t energy phosphorescence band o f t h e bc_' s e c t i o n t o r e d - s h i f t by 80 cm Traps o f t y p e 2 were r e a d i l y o b s e r v e d above about 20°K when another broad phosphorescence o r i g i n , about 320 cm  1  to the red o f the f i r s t ,  gradually  i n c r e a s e d i n s t r e n g t h (see F i g . 5 2 ) . The double maxima i n I^p i s a p p a r e n t l y a consequence and- T  2  o f t h e t r a p s T^ emptying i n t h e t e m p e r a t u r e range 20-30°K  i n t h e range 40-50°K.  From t h e v a r i o u s p l o t s shown i n F i g . 53, t h e o n l y s a t i s f a c t o r y t r a p d e p t h was f o r T^ which was found t o be 670 cm . 1  phosphorescence o r i g i n band a t 22 580 cm the  band gap o f 23 250 cm  1  The c o r r e s p o n d i n g (broad)  g i v e s an independent e s t i m a t e f o r  Because o f t h e extreme w i d t h o f t h e phos-  p h o r e s c e n c e bands, t h e assumption t h a t a l l t h e t r a p s l i e a t t h e same energy below t h e b a n d i s p r o b a b l y u n s a t i s f a c t o r y .  T h i s may a l s o account f o r t h e  n o n - l i n e a r i t y o f t h e o t h e r p l o t s i n F i g . 51. T r i p l e t - t r i p l e t a b s o r p t i o n was observed i n t h e b i p h e n y l c r y s t a l doped w i t h d i b e n z o t h i o p h e n e , and t h e s p e c t r a ( a t about 10°K) a r e shown i n F i g . 54. 136 For  c o m p a r i s o n , t h e spectrum observed  triplet' absorption i n a r i g i d  by Ramsay and Munro  g l a s s a t 77°K i s a l s o g i v e n .  of t r i p l e t Although the  bands a r e b r o a d , t h e y a r e s p l i t s u f f i c i e n t l y t o i n d i c a t e t h e p r e s e n c e o f two e l e c t r o n i c t r a n s i t i o n s o f o p p o s i t e p o l a r i z a t i o n .  No r e l i a b l e  assign-  ment o f t h e symmetry o f t h e l o w e s t t r i p l e t ' s t a t e has been made. The 137 r e s u l t s o f Stewart's c a l c u l a t i o n f o r planar biphenyl i n d i c a t e that the  215  2800 -  F i g . 52 *'DF  Temperature  variation  o f t h e i n t e n s i t y o f t h e phosphorescence  ( I p ^ and Ip ) and  of the delayed fluorescence ( I p ) from a b i p h e n y l n  crystal  doped w i t h d i b e n z o t h i o p h e n e - h  o  T E M P E R A T U R E  °K  t h e o r b i t a l symmetry o f t h e l o w e s t - t r i p l e t s t a t e may be  B  2 u  which, i n t h i s  c a s e , t r a n s f o r m s l i k e an i n - p l a n e v e c t o r p a r a l l e l t o t h e y_ a x i s (see F i g . 5 ) . I f t h i s assignment i s a c c e p t e d , t h e n t h e v i b r o n i c t r a n s i t i o n s a r e : 3 3 Ag«<— 2 u B  5  P  a  r  a  H l e  t o t h e s h o r t i n - p l a n e a x i s a t low energy, and  3  —  B  3 2u'  p a r a l l e l t o t h e long a x i s a t h i g h e r energy. The e x p e r i m e n t s c a r r i e d out on b i p h e n y l doped w i t h d i b e n z o t h i o p h e n e - d  o show no measureable s h i f t i n t h e wavelength o f t h e i n d u c e d phosphorescence  CH + D F  OP) AS A w  .Q  2  ' D F  -1  H—  o Q:  A O  >, CO  (AE=670cm-'  -2  A  A  c H—  c CP  3  O -3  oooooooooooo O O O O  O  o  o  o  -4H  .02  .03  .04  .05  .06  .07  .08  .09  1/T F i g . 53  P l o t s o f l o g ( i n t e n s i t y r a t i o s ) v s 1/T f o r t h e d i b e n z o t h i o p h e n e - h / b i p h e n y l g  system,  - 217 -  :  LJ  £  i  24000  F i g . 54  Solid  i  i  26 000  line triplet-triplet  l  28 000  J  Cm~'  a b s o r p t i o n i n a b i p h e n y l c r y s t a l doped  w i t h d i b e n z o t h i o p h e n e at about 10°K.  Broken l i n e :  triplet-triplet  a b s o r p t i o n o f b i p h e n y l i n a r i g i d g l a s s a t 77°K ( a c c o r d i n g t o 136  Ramsay and Munro  ) .  from t h a t o b s e r v e d w i t h d i b e n z o t h i o p h e n e - h  as g u e s t .  The  temperature  o  dependence o f t h e i n t e n s i t y (compare F i g . 52 and 5 5 ) .  o f the l i g h t e m i s s i o n a r e q u a l i t a t i v e l y A pronounced d e l a y e d f l u o r e s c e n c e from  similar phenanthrene  and t o a lesser e x t e n t from a n t h r a c e n c e became e v i d e n t above about 25°K and the system was not s t u d i e d f u r t h e r .  The phenanthrene  and a n t h r a c e n e were p r e s e n t  i n t h e commercial b i p h e n y l - d ^ Q , and t h e r e was i n s u f f i c i e n t s t a r t i n g f o r complete p u r i f i c a t i o n and  synthesis.  material  2800  - 21 Al  D  AI  d  F  f  2600  (DBT-d ) 8  (Phenanthrene)  o Ip 2400  22COH  2000  I S O O  1600  1400  1200  I O O O  800H  600H  400  200  40  50  60  T E M P E R A T U R E °K Temperature v a r i a t i o n : ooff tthhee iinntteennssiittyy ooff tthhee phosphorescence fl„ and I ) , ) from a b. Ki p h. e *n y l " c r v s t a l vand , ^ ^ ^o ^ -f^ "the'delayed -l,„,1„T 1,-1f l u o r e s c e n c e ( I r1 ^2 doped w i t h dibenzothiophene-dg. . n p  - 219 -  Appendix I  The A b s o r p t i o n and F l u o r e s c e n c e  Spectrum o f C a r b a z o l e  i n a Biphenyl Matrix  T a b l e 48.  //b  The a b s o r p t i o n spectrum o f c a r b a z o l e i n b i p h e n y l a t about 15°K.  //c  Int.  Remarks origin  29-698  lattice  27 218  vs  218, A  420  s  420,  432  ms  2 x 218 - 4  505  m  505?  515  m  515, B  2  577  mw  577, B  2  650  vs  650, A  720  ms  720,  729  vw  218  793  vw  218 + 5 7 7 - 2  s  218  vs  928, B  936  m  218  985  vs  985,  864 928  A.  A  1  +505+6  +650-4 2  +720+2 A  991, B  991  1  2  s  985  1034  s  1034,  B  2  1119  vs  1119, B  2  w  420 + 720 + 1  m  515  m  48 + 9 8 5 - 2  m  218 + 9 9 1 - 5  1238  vs  1238,  1299  s  2 x 650 - 1  1006  1141 1161 1201 1204  +27+4  +650-4  A  1  - 220 -  //b  //c  Int.  1339  s  218  +  1119 + 2  ms  218  +  1238 - 5  mw  1486,  m  218  ms  1543,  B  m  1545,  A  1451 1486 1512 1543 1545  Remarks  650  1573  2 2 x 650 - i  B  +  +  2  l 928 - 5  1596  m  1596,  1630  mw  650  +  l 985 - 5  m  650  +  991 - 4  w  420  +  1238 - 6  mw  650  +  1034 - 4  w  720  +  985  m  650  +  1119 - 2  w  218  +  1596 -• 4  w  577  +  1238 - 4 •  1848  mw  218  +  650 + 985  1882  m  650  +  1238 - 6  1945  m  3 x 650 - 5  1959  mw  720  1981  w  2 x 218 + 1545  w  218  2018  w  2 x 650 + 720 -  2096  w  218  +  650 + 1238  2163  w  928  +  1238 - 3  2193  w  650  +  1543  m  985  +  1238 -• 4  w  991  +  1258 -• 3  2242  m  650  +  1596 -• 4  2281  m  2 x 650 + 985 -  2309  mw  720  +  1596 -• 7  2321  mw  985  +  1339 -• 1  2353  mw  1119 + 1238 - 4  1637 1652 1680 1705 1767 1810 1811  1986  2219 2226  +  +  A  1238  4  1  650 + 1119  - 221 -  //b  //£  Int.  Remarks  2436  mw  218 + 985 + 1238 - 5  2470  mw  2 x 1238 - 6  2535  mw  2 x 650 + 1238 - 3  2781  vw  1238 + 1543  2866  vw  650 + 985 + 1238 - 7  . . . -1 The p o s i t i o n o f t h e o r i j ; and a l l o t h e r ; i n i s g i v e n cm d i f f e r e n c e s from t h e o r i g i n .  e n t r i e s show  The spectrum exhibite<J d o u b l e t v i b r o n i c s t r u c t u r e w i t h o r i g i n s a t 29 678 and 29 698 cm . Only those l i n e s a s s o c i a t e d w i t h 29 698 cm" o r i g i n are included i n the t a b l e .  30,000 . 56  30,500  31,OOO  31,500  The p o l a r i z e d a b s o r p t i o n spectrum o f c a r b a z o l e i n b i p h e n y l a t about  32,000 15°K.  cm  - 223 T a b l e 49.  f l u o r e s c e n c e spectrum o f c a r b a z o l e i n b i p h e n y l a t about 15°K  The  //b  •//£'  Remarks  Int. origin  29 698  (reabsorbed)  57  w  lattice  85  m  lattice  121  w  lattice  142  w  lattice  218  vvs  218,  A  x  427  m  427,  A  :  438  ms  2 x 218 + 2  470  w  2 x 218 +  552  m  552,  B  2  618  m  618,  B  2  655  vvs  655,  A  x  744  w  744,  A  x  770  w  218 + 552  834  w  218  +618-2  874  s  218  +655+1  898  s  898,  960  vw  218  w  988,  1012  ms  1012,  1094  w  2 x 218 + 655 + 3  m  1117,  1144  mw  1144,  A  1208  m  1208,  A  ms  1222,  1233  m  218 + 1012 + 3  1285  s  1285,  1312  s  2 x 655 + 2  1337  s  1337,  A  x  ms  1394,  B  2  w  1454,  A  :  988  1117  1222  ' 1454  1394  A  lattice  :  +743-1 B  2  A  1  B  2  i  l  B  A  2  }  - 224 -  //b_  //c  1  Int.  Remarks  m  1460, B  2  mw  1484, A  x  mw  1489, B  2  1505  m  218 + 1285 + 2  1530  m  218 + 2 x 655 + 2  1555  m  218 + 1337  1578'  w  1578, A  :  ms  1606, B  2  1629  ms  1629, A  2  1668  m  655 + 1012 + 1  1680  w  218 + 1460 + 2  1710  w  218 + 1489 + 3  vw  655 + 1144 + 2  w  552 + 1285 - 2  1845  mw  218'+ 1629 - 2  1884  w  218 + 655 + 1012 -  1940  m  655 + 1285  1967  m  3 x 655 + 2  1991  m  655 + 1337 - 1  2018  vw  2 x 1012 - 6  2049  w  655 + 1394  2119  vw  655 + 1460 + 1  w  1012 + 1144 + 8  w  655 + 1606 + 5  2282  mw  655 + 1629 - 2  2299  mw  1012 + 1285 + 2  2324  mw  1460 1484 1489  1606  1797 1835  2160 2266  . mw  2349  . 2 x 655 + 1012 + 2 1012 + 1337  vw  1208 + 1285 + 8  w  2 x 1285 + 2  2598  w  2 x 655 + 1285 + 3  2622  mw  1285 + 1337  2642  • mw  2501 2568  /  2 x 655 + 1337 - 5  - 225 -  //b  //£'  Int.  Remarks •  w  2 x 1337 - 1  w  2 x 655 + 1394 + 4  vw  218 + 2 x 655 + 1285 + 6  vw  1285 + 1607 - 1  w  1285 + 1629 - 3  mw  2 x 655 + 1606 - 1  . 2936  mw  2 x 655 + 1629 - 3  2962  mw  1337 + 1629 - 4  3082  w  C-H  vw  1606 + 1629 - 4  3253  w  2 x 1629 + 1  3279  w  5 x 655 - 4  3421  w  N-H  2673 2708 2819 2890 2911 ' 2915  3231  The p o s i t i o n o f t h e o r i g i n i s g i v e n i n cm d i f f e r e n c e s from t h e o r i g i n .  -1  and  stretch?  stretch?  a l l o t h e r e n t r i e s show  b-.axis  27,000 F i g . 57  27,500  28,000  The f l u o r e s c e n c e , spectrum o f c a r b a z o l e  i n biphenyl  28,500 a t about  15°K.  29,000  29,500  cm  - 227 Appendix I I  Table  50.  A comparison  o f t h e assignments  o f t h e fundamentals f o r  carbazole , f l u o r e n e , dibenzothiophene  ( D B T - h ) , and dibenzo0  o  thiophene-d  c  (DBT-d )  Species  Carbazole  A  220  217  215  199  425  421  403  390  628  494  484  747  743  712  664  856  857  854  828  934  866  x  658  Fluorene  '  910  DBT-h  G  o  DBT-d, c  1012  1016  1026  911  1107  1089  1068  1059  1136  1186  1133  1125  1205  1231  1203  1175  1288  1291  ' 1233  1201  1319? 1334  1349  1283 1318  1397 1449  1440  1421  1320  1481  1480  1475  1417  1576  1570  1557  1521  1625  1612  1593  1568  3039  2920?  3000  2225  3055  3018  3025  2271  3077  3048  3055  2284  3084  3064  --  2309  3421  3094?  -  Species  Carbazole  228 -  Fluorene  DBT-h  0  o B  2  .  Species A  DBT-d  0  o  505  487  496  472  548  542  560  492  616  618  613  592  737?  722?  704  672  835  904?  865  775  995  994  966  815  1022  1023  1001  833  1118  1103  1074  855  1158  1146  1156  948  1204  1188  '--  1233  1215  1268  1160  1320  1303-  1314  1286  1380  1336  1353  1335  1452  1440  1442  1380  1490  1471  1462  1446  1594  1521  1514  1478  2940  3006?  3025  3030  3040  --  --  3050  3062  3055  --  3094?  3084?  3117  --  Fluorene  DBT-h.  DBT-d  Carbazole  • --  8  o 156  2  299  287  287  251 385 645  788  746  - 229 -  Species  Carbazole  Fluorene  DBT-h  DBT-d  139  119  138  128  310  260  226  217  445  473  424  366  566  693  724  421  722  735  744  561  741  841  770  622  --  873  859  720  880?  910  895  762  926  951  940  845  152  1153 2905?  - 230 -  References  1.  M. Born and K. Huang, Dynamical Theory o f C r y s t a l L a t t i c e s , O x f o r d U n i v e r s i t y P r e s s , London and New Y o r k , 1954.  2.  M. Tinkham, Group Theory and Quantum M e c h a n i c s , M c G r a w - H i l l , New Y o r k , 1964  3.  F.M. G a r f o r t h , C.K.. I n g o l d , and H.G. P o o l e , J . Chem. Soc. 1948, 406  4.  G. H e r z b e r g and E. T e l l e r , Z. P h y s i k . Chim. B21, 410 (1933).  5.  A.D. L i e h r , Z. N a t u r f o r s c h . 13a, 311 (1958).  6.. J.N. M u r r e l l and J.A. P o p l e , P r o c . Phys. Soc. (London) A69, 245 (1956). 7.  D.P. C r a i g , J . Chem. Soc. 1950, 59  8.  A.C. A l b r e c h t , J . Chem. Phys. 33, 156 (1960).  9.  W.A. Y e r a n o s , Z. N a t u r f o r s c h . 22a, 183 (1967).  10.  E.F. McCoy and I.G. Ross, A u s t . J . Chem. 15_, 573 (1962).  11.  A. Grabowslca,  12.  J.B. Coon, R.E. de Wames, and C M . L l o y d , J . M o l . S p e c t r y . 8_, 285 (1962).  13.  K. M i l l e r and J.N. M u r r e l l , T h e o r e t . Chim. A c t a ( B e r l . ) 2, 231 (1965).  14.  K. M i l l e r and J.N. M u r r e l l , T h e o r e t . Chim. A c t a ( B e r l . ) 1_, 69 (1967).  15.  A. Breeand  16.  A.S. Davydov, Theory o f M o l e c u l a r E x c i t o n s , M c G r a w - H i l l I n c . , New Y o r k , N.Y., 1962.  17.  D.P. C r a i g and S.W. Walmsley, P h y s i c s and C h e m i s t r y o f t h e Organic S o l i d S t a t e , Ed. D. Fox, M. Labes, and A. W e i s s b e r g e r , I n t e r s c i e n c e P u b l i s h e r s , .1963.  18.  D.S. M c C l u r e , E l e c t r o n i c S p e c t r a o f M o l e c u l e s and Ions i n C r y s t a l s , Academic P r e s s , New York and London, 1959.  19'.  D.P. C r a i g and S.W. Walmsley, E x c i t o n s i n M o l e c u l a r C r y s t a l s , Benjamin, I n c . , New Y o r k , N.Y., 1968.  J . M o l . S p e c t r y . 20, 96 (1966).  L. L y o n s , J . Chem. Soc. (London) 1956, 2658.  W.A.  - 231 -  20.  S.A. R i c e and J . J o r t n e r , P h y s i c s and C h e m i s t r y o f t h e O r g a n i c S o l i d S t a t e , V o l . I I I . Ed. D. Fox, M. Labes, and A. W e i s s b e r g e r , I n t e r s c i e n c e P u b l i s h e r s , 1967.  21.  H. Winston and R.S. H a l f o r d .  22.  H. W i n s t o n , J . Chem. Phys. 19, 156 (1951).  23.  G.F. K o s t e r , S o l i d S t a t e Phys. _5, 173 (1957).  24.  D.P. C r a i g and T.Thirunamchandran,  25.  D.P. C r a i g and P.C. Hobbins, J . Chem. Soc. 1955, 539.  26.  D.P. C r a i g and J.R. Walsh, J . Chem. Phys. 25, 588 (1956).  2.7.  D.P. C r a i g and S.H. Walmsley, M o l . Phys. 4_, 113 (1961).  28.  W.T. Simpson and D.L. P e t e r s e n . J . Chem. Phys. 26., 588 (1957).  29.  R.M. H o c h s t r a s s e r , Rev. Mod. Phys. 34, 531 (1962).  30.  D.S. M c C l u r e , J . Chem. Phys. £ 2 , 1668 (1954).  31.  N.K. Choudhury and S.C. Ganguly, 1960.  32.  D.P. C r a i g and T.Thirunamachandran 207 (1963).  33.  E. W i l s o n , J.C. D e c i u s , and P.C. C r o s s , M o l e c u l a r V i b r a t i o n s , McGrawH i l l Book Co., I n c . , New Y o r k , N.Y., 1955.  34.  G.Herzberg, I n f r a r e d and Raman S p e c t r a o f P o l y a t o m i c M o l e c u l e s , Van N o s t r a n d , New York, 1945.  35.  H.C. Urey and C.A. B r a d l e y , Phys. Rev., 3_8, 1969 (1931). ,  36.  D.D. P h i l l i p s , Org. Syntheses  37.  E.A. Johnson, J . Chem. Soc. 1962, 994.  38.  E.H. Rodd, C h e m i s t r y o f Carbon Compounds. New York (1956) .  39.  Y. Kanda, R. Shimada, K. Hanada and S. K a j i g a e s h i , S p e c t r o c h i m . A c t a 1 7 , 1268 (1961) .  40.  J.H. W e i s b e r g e r  41.  R.M.  i /  J . Chem. Phys. 17_, 607 (1949).  P r o c . Phys. Soc. 84, 781 (1964).  P r o c . Roy. Soc. (London) A259, 419, P r o c . Roy. Soc. (London), A271,  34_, 31 (1954):  Vol. IIIB, Elsevier,  and P.H. Grantham, J . Org. Chem. 2_1, 1160 (1956).  H o c h s t r a s s e r and G. S m a l l , J . Chem. Phys. 45, 2270 (1966).  - 232 -  42.  R.C.  S o n g s t e r .and S.W.  I r v i n e , J r . , J . Chem. Phys. 24_, 670 (1956).  43.  H. Gilman and A.L. J a c o b y , J . Org. Chem. 3_, 108  44.  P.W. Bridgman, P r o c . Am. Acad. A r t s . S c i . , 6£, 303 (1925).  45.  A.N. W i n c h e l l , The O p t i c a l P r o p e r t i e s o f O r g a n i c Compounds, Academic P r e s s , New Y o r k , 1954.  46.  W.H. D u e r i g and I.L. Mador, Rev. S c i . I n s t r . 23, 421 (1952).  47.  V. R o b e r t s . J . S c i . I n s t r . 3_2, 294 (1955).  48.  A.H. Woodcock, Can. J . Res., 16A, 133 (1938).  49.  N.H. H a r t s h o r n e and A. S t u a r t , C r y s t a l s and The P o l a r i z i n g 3 r d . Ed., Edward A r n o l d L t d . , 1960.  50.  A. Bree and T. Thirunamachandran, M o l . Phys. 5_, 397 (1962).  51.  H.R. Wyss, R.D. Wender, and H. Gunthard, (1964).  52.  W.R. Erode, Chemical S p e c t r o s c o p y , 2nd. Ed., John W i l e y and Sons, I n c . , New Y o r k , 1943.  53.  H. K a y s e r ,  54.  J . T r o t t e r , A c t a C r y s t . 14, 1135 (1961).  55.  G.B. R o b e r t s o n , N a t u r e 191, 593 (1961).  56.  A. Almenningen and 0. B a s t i a n s e n , S k r i f t e r , no. 4 (1958).  57.  D.M. B u r n s , and J . I b a l l , P r o c . Roy. Soc. (London) A227, 200 (1955).  58.  M. K u r a h a s h i , M. Fukuyo, A. Shimada, A. F u r u s a k i and I . N i t t a , Chem. Soc. Japan 39, 2564 (1966).  59.  M. K u r a h a s h i , p e r s o n a l  60.  S. W h i t l o w , p e r s o n a l  61.  R. S c h a f f r i n and J . T r o t t e r , p e r s o n a l  62.  W. Bruhn and R. Mecke, Z. E l e c t r o c h e m . 65_, 543 (1961).  63.  W. Bruhn and A. C h a f i k , Z. N a t u r f o r s c h 199, 41 (1964).  64.  S, C a l i f a n o , J . Chem. Phys. 36, 903 (1962).  T a b e l l e d e r Schwingungszahlen  (1938/1939).  Microscope,  S p e c t r o c h i m . A c t a . _20, 573  S. H i r z e l i n L e i p z i g , 1925.  K e g l . Norske V i d e n s k a b e r s S e l s k a b s  communication. communication communication  Bull.  C )  - 233 -  65.  N. Neto, M. S c r o c c o and S. C a l i f a n o , S p e c t r o c h i m . A c t a _22, 1981 (1966).  66.  L. Colombo, S p e c t r o c h i m . A c t a 20, 547 (1964).  67.  N. Abasbegovic, N. V a k o t i c and L. Colombo, J . Chem. Phys. 41_, 2575 (1964)  68.  A. B r e e , S. K a t a g i r i and S.R. S u a r t , J . Chem. Phys. 44_, 1788 (1966).  69.  A. .Bree and R.A. Kydd, J . Chem. Phys. 48,'5319 (1968).  70.  M. I t o , M. Suzuko and T. Yokoyama, B u l l . Chem. Soc. Japan 4£, 2461 (1967).  71.  M. S u z u k i , T. Yokoyama and M. I t o , S p e c t r o c h i m . A c t a 24A, 1091 (1968).  72.  J . Gay, R. K a r a and J.P. M a t h i e u , B u l l . Soc. France. M i n e r a l C r i s t . 84_, 189 (1961).  73.  V. S c h e t t i n o , N. Neto and S. C a l i f a n o , J . Chem. Phys. 44, 2724 (1966).  74.  V. S c h e t t i n o , J . Chem. Phys. 4i5, 302 (1967).  75.  K. W i t t and R. Mecke, Z. N a t u r f o r s c h . 22a, 1247 (1967).  76.  D.P. C r a i g and R.D. Gordon, P r o c . Roy. Soc. (London) A288, 69 (1965).  77.  N. Neto, F. Ambrosino and S. C a l i f a n o , S p e c t r o c h i m . A c t a 20_, 1503 (1964).  78.  G. Abbondanza and S. C a l i f a n o , J . Chem. Phys. 39^ 1016 (1963).  79.  F. Ambrosino and S. C a l i f a n o , S p e c t r o c h i m . A c t a . 21_, 1401 (1965).  80.  J o i n t Commission f o r S p e c t r o s c o p y , J . Chem. Phys. 23_, 1997 (1955).  81.  G.B..Bonino and R. M a n z o n i - A n s i d e i , R i c . S c i . 8_, I I , 354 (1937).  82.  R.M. H o c h s t r a s s e r and G.J. S m a l l , J . Chem. Phys. 48, 3612 (1968).  83.  A. Bree and S. K a t a g i r i , J . Mol. S p e c t r y . 1_7, 24 (1965).  84.  A.R. Lacey, R.G. Body, G. Frank, and I.G. Ross, J . Chem. Phys. £ 7 , 2199 (1967) . .  85.  N. Mataga, Y. T o r i h a s h i and K. Ezumi, T h e o r e t . Chim. A c t a 2, 158 (1964).  86.  D.H. W h i f f e n , P h i l . T r a n s . Roy. Soc. A248, 131 (1955).  87.,  D.J. Evans, and D.B. S c u l l y , S p e c t r o c h i m . A c t a 20, 891 (1964).  88.  J.H. S c h a c h t s c h n e i d e r , S h e l l Development Co., t e c h n i c a l r e p o r t no. 57-65.  234 -  89.  S. S i e g e l and H.S. J u d e i k i s , J . Phys. Chem. 7TJ, 2205 (1966).  90.  H. S c h u t t and H. Zimmerman, Bunsen. Phys. Chem. 67, 54 (1963).  91.  C.A. Pinkham and S.C. W a i t , J . M c l . S p e c t r o s c . 27, 326 (1968).  92.  G. F a v i n i and A. Gamba, Gazz. Chim. I t a l . 9_8, 627 (1968).  93.  A. Bree and V.V.B. V i l k o s , J . Chem. Phys. 40, 3125 (1964).  94.  O.H. G r i f f i t h , J . Phys. Chem. 69, 1429 (1965).  95.  S.W. C h a r l e s , P.H.H. F i s c h e r and C.A. McDowell, M o l . Phys. 9_, 517 (1965).  96.  R.N. Nurmukhametov and G.V. Gobov, Opt. S p e c k t r o s k . 13_, 676 (1962) [Opt. S p e c t r o s c . L 3 , 384 ( 1 9 6 2 ) ] .  97.  M. Nakamizo and Y. Kanda  98.  M. Barbaronand  99.  P. P e s t e i l and L. P e s t e i l , C.R. Acad. S c i . , P a r i s 254, 75 (1954).  S p e c t r o c h i m . A c t a . 1_9, 1235 (1963).  P. P e s t e i l , C.R. Acad. S c i . , P a r i s 238, 1400 (1954).  100.  M. Benarroche, C.R. Acad. S c i . , P a r i s 254, 3520 (1962).  101.  C.A. P a r k e r , C.G. H a t c h a r d and T.A. J o y c e , A n a l y s t . 90, 1 (1965).  102.  H.H. L a n d o l t and R. B o r n s t e i n , P h y s i k a l i s c h e - C h e m i s c h e T a b e l l e n Band I T e i l 2, S p r i n g e r - V e r l a g , B e r l i n (1951).  103.  D.P. C r a i g , J.M. H o l l a s , M.F. Redies and S.C. W a i t , P h i l . T r a n s , Roy. Soc. (London) A253, 543 and 569 (1961).  104.  R.L. Hummel and K. Ruedenberg, J . Chem. Phys. 66, 2334 (1962).  105.  E.M. L a y t o n , J . M o l . S p e c t r o s c . 5_, 181 (1960).  106.  J.R. P i a t t , J . Chem. Phys. 19_, 101 (1951).  107.  A. Bree and L.E. Lyons, J . Chem. Soc. 1956, 2658  108.  E.V. S h p o l s k i i , Usp. F i z . Nauk. SfJ, 255 (1963) . [ S o v i e t P h y s i c s Usp. 6_, 411 ( 1 9 6 3 ) ] .  109.  V.V. Trusov and P.A. T e p l y a k o v . Opt. S p e k t r o s k . 16_, 52 (1964).  110.  P.A. T e p l y a k o v ; V . I . M e l n i k , V . I . M i k h a i l e n k o , and V.V. T r u s o v , Opt. Spektrosk'. _22, 57 (1967).  111.  R. Heckman, J . M o l . S p e c t r o s c . 2, 27 (1958).  - 235 -  112.  G. P o r t e r and M.W.Windsor, P r o c . Roy. Soc. (London) A245, 238 (1958).  113.  D.P. C r a i g and I.G. Ross, J . Chem. Soc. 1954, 1589  114.  A. Bree and R. Kydd.  115.  D.F. Evans, J . Chem. Soc. 1957, 1351.  116.  F. Dorr (1963).  117.  K. W i t t , S p e c t r o c h i m . A c t a 24A, 1115 (1968).  118.  R. M a n z o n i - A n s i d e i , Redd. Accad. L i n c e i , 2j5, 266 (1937).  119.  T.A. H a r i h a r a n , J . I n d . I n s t . S c i . 36A, 215 (1954).  120.  J . B e h r i n g e r and J . B r a n d m u l l e r , Z. Angew. Phys. 1_4, 674 (1962).  121.  G.W.H. S c h e r f and R.K. Brown, Can. J . Chem. 38, 697 (1960).  122.  See, f o r example, e q u a t i o n (28) i n r e f e r e n c e 12.  123.  F. D o r r , Agnew. Chem. i n t e r n a t . E d i t . 5_, 478 (1966).  124.  R.N. Nurmukhametov and G.B. Gobov, Opt. S p e k t r o s k . 1_8, 227 (1965).; [Opt. S p e c t r o s c . L8, 126 ( 1 9 6 5 ) ] .  125.  M. B i e l e f i e l d and D. F i t t s , J . Am. Chem. Soc. 8_8, 4804 (1966) and references c i t e d therein.  126.  J . Koutecky, R. Zahradnik and J . P a l d u s , J . Chim. Phys. 56_, 455 (1959).  127.  H. S t e r n l i c h t , G.C. Nieman, and G.W. (1963); i b i d 39, 1610 (1963).  128.  R.M. H o c h s t r a s s e r , J . Chem. Phys. 39, 3153 (1963).  •129.  G. C a s t r o and R.M. H o c h s t r a s s e r , J . Chem. Phys. 46, 3617 (1967).  130.  D.F. W i l l i a m s , J . Chem. Phys. 47_, 344 (1967).  131.  H.P. M u l l e r , P. Thoma, and G. V a u b e l , Phys. S t a t . S o l . 23_, 253 (1967).  132.  G.C. S m i t h , Phys. Rev. 166, 839 (1968).  133.  H. P o r t and H.C  134.  T.N. M i s r a and S.P. McGlynn, J . Chem. Phys. 44, 3816 (1966).  135.  N.J. H i r o t a , J . Chem. Phys. 44, 2199 (1966).  ( t o be p u b l i s h e d ) .  and H. Gropper, .  B e r . Bunsenges. P h y s i k . Chem. 6 7 193 ~ >  Robinson, J . Chem. Phys. 38, 1326  W o l f , Z. N a t u r f o r s c h . 23a, 315 (1968).  -  236  -  136.  I . A . Ramsay and l . H . Munro. The T r i p l e t S t a t e , ed. A.B. (Cambridge U n i v e r s i t y P r e s s , 1967) p. 415.  137.  E.T.  S t e w a r t , J . Chem. Soc.  1958,  4016.  Zahlan  

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