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Some chiroptical effects on the photophysics and photochemistry of tris(bipyridine)ruthenium(II) ions… Sparks, Robert Henry 1979

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SOME CHIROPTICAL EFFECTS ON THE PHOTOPHYSICS AND PHOTOCHEMISTRY OF TRIS(BIPYRIDINE)RUTHENIUM(II) IONS IN SOLUTION  By  ROBERT HENRY SPARKS  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in  THE FACULTY OF GRADUATE STUDIES (Department o f C h e m i s t r y )  We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o "the r e q u i r e d s t a n d a r d  THE UNIVERSITY OF BRITISH COLUMBIA AUGUST, 1979  ©  Robert Henry Sparks  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives.  It is understood that copying or publication  of this thesis for financial gain shall not be allowed without my written permission.  Department The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5  E-S  B P 75-5 1 1 E  ii  ABSTRACT:  The p h o t o r a c e m i z a t i o n of R u ( b i p y ) ^  i n aqueous s o l u t i o n was s t u d i e d .  3 Quenching s t u d i e s show the involvement  | |  o f t h e (CT) R u ( b i p y ) ^  i n the mech-  -4 anism of r a c e m i z a t i o n and the low quantum y i e l d t h i s s t a t e i s asymmetric.  (2.9 x 10  ) shows t h a t  Quenching s t u d i e s show no i n c r e a s e of r a c e m i z a -  t i o n r a t e f o r Ru(I) o r ( I I I ) s p e c i e s .  The temperature  evidence f o r a d i s s o c i a t i v e r a c e m i z a t i o n mechanism.  dependence g i v e s  Quenching w i t h Co(acac)  shows c h i r o s e l e c t i v e e l e c t r o n t r a n s f e r as measured by t h e r e s u l t i n g chemistry.  photo-  iii  TABLE OF CONTENTS  PAGE  Introduction  1  Background  2  Experimental  7  R e s u l t s and D i s c u s s i o n  •  14  Conclusions  28  Appendix A  30  Appendix B  33  References  34  LIST OF TABLES  Table I  17  Table I I  19  Table I I I  19  T a b l e IV  33  LIST OF FIGURES  Figure 1  4  Figure 2  9  Figure 3  13  Figure 4  20  Figure 5  21  Figure 6  22  Figure 7  25  Figure 8  27  iv  ACKNOWLEDGEMENTS: I would l i k e to thank Professor G.B. Porter for his patient supervision, and guidance during t h i s project.  For his useful  teaching,  discussion,  I would l i k e to thank Professor L . D . Hayward as well as other members of the Faculty of Chemistry and t h e i r supporting s t a f f . thank those who have worked i n lab 244: Dr. J . Van Houten. we a l l explore.  C.P.J.  Also, I would l i k e to  Bennington, K. Sarantidis,  Most of a l l I wish to thank God for his creation which  INTRODUCTION: Over t h e l a s t decade t h e r e has been a r a p i d i n c r e a s e i n t h e amount o f I| l i t e r a t u r e p u b l i s h e d on t h e t r i s ( b i p y r i d i n e ) r u t h e n i u m ( I I ) i o n ( R u ( b i p y ) ^ ) • T h i s i s p a r t l y due t o i t s i n t e r e s t i n g i n t e r a c t i o n s w i t h l i g h t . t i o n spectrum shows q u i t e i n t e n s e bands ( e  /  r  HOZ  M'crn)  o  The a b s o r p -  4 = 1.29 x 10 , e „  0 £  zoo  4 = 7.67 x 10 )  The symmetry l a b e l s and m u l t i p l i c i t i e s o f the e x c i t e d s t a t e s have 2-9  been d i s c u s s e d a t l e n g t h i n t h e l i t e r a t u r e .  The i n t e n s e a b s o r p t i o n t o I )  gether w i t h t h e l o c a t i o n o f v a r i o u s e x c i t e d s t a t e s make R u ( b i p y ) ^  a good  c a n d i d a t e f o r i n c l u s i o n i n s o l a r energy r e s e a r c h . T h i s complex i o n a l s o emits s t r o n g l y w i t h a l i f e t i m e of 0.6 us. ^  approximation  The l i f e t i m e i s of a c o n v e n i e n t  l e n g t h f o r s t u d y i n g t h e quenching 12-14 e f f e c t s o f o t h e r m o l e c u l e s on t h e l u m i n e s c e n c e . I| The e x c i t e d s t a t e of R u ( b i p y ) ^ a l s o e x h i b i t s c o n s i d e r a b l e p h o t o c h e m i s t r y b o t h o f a permanent and s h o r t l i v e d o r t r a n s i e n t n a t u r e . Examples o f a t r a n s lent photochemistry  3+ 15 a r e the o x i d a t i o n t o Ru(bipy)^ and t h e r e d u c t i o n o f  n i t r o g e n s u b s t i t u t e d 4 , 4 - b i p y r i d i n e d e r i v a t i v e i n t h e absence o f EDTA.^ For permanent p h o t o c h e m i s t r y ,  as w e l l a s o x i d a t i o n s  17  and r e d u c t i o n s  18  19 20 there are p h o t o s e n s i t i z a t i o n , photolysis reactions, and p h o t o a n a t i o n 21 reactions. Ij I n t h e c o n t e x t o f t h e above r e a c t i o n s t h e R u ( b i p y ) ^  i srelatively  15 18 and can undergo e l e c t r o n t r a n s f e r s ' and e x c i t a t i o n s w i t h o u t ridine ligands. stability.  22 23 '  inert  l o s s o f t h e bipy-  The o p t i c a l a c t i v i t y has a l s o been shown t o have g r e a t O p t i c a l s t a b i l i t y d u r i n g o x i d a t i o n has a l s o been shown.  thermal 2A  ++ 25 R e c e n t l y i t was suggested t h a t R u ( b i p y ) ^ i s chiroptically stable to excitation. T h i s i s i n f a c t n o t t h e c a s e , as i s shown i n t h i s work on t h e p h o t o r a c e m i z a I [ t i o n of Ru(bipy)^ •  - 2 BACKGROUND Ru(bipy)  3  The a b s o r p t i o n near 450 nm i n t h e spectrum o f R u ( b i p y ) ^ has been s u g gested t o represent  transitions.  d->-rr  i n a m a i n l y m e t a l d o r b i t a l i s promoted  T h i s would mean an e l e c t r o n w h i c h i s t o a l i g a n d IT o r b i t a l , w h i c h  l o c a l i z e s t h i s e l e c t r o n m a i n l y on t h e l i g a n d s .  P r o t o n a t i o n experiments  support t h i s view i n the increased b a s i c i t y of the l i g a n d s i n t h e e x c i t e d 26 state.  A change i n t h e m e t a l - l i g a n d bond s t r e n g t h s and a g r e a t e r l i g a n d -  l i g a n d r e p u l s i o n i n t h e e x c i t e d s t a t e over t h e ground s t a t e i s e v i d e n t . * 3 T h i s d-Mr e x c i t e d s t a t e w i l l be r e f e r r e d t o i n t h i s paper a s (CT) R u ( b i p y ) i n s p i t e of the ambiguity of t h i s  labelling.  3 | | (CT) R u ( b i p y ) ^ can r e t u r n t o t h e ground s t a t e t h r o u g h a number o f routes:  i t c a n l u m i n e s c e ; i t can t r a n s f e r energy and/or an e l e c t r o n t o o r  from a n o t h e r m o l e c u l e .  Energy t r a n s f e r a l o n e i s p r e f e r r e d i n o r g a n i c s o l -  27 vents.  Energy t r a n s f e r p r o c e s s e s c a n g i v e r i s e t o p h o t o c h e m i s t r y o f t h e 3 ++ quencher. When t h e quencher r e c e i v e s an e l e c t r o n from (CT) R u ( b i p y ) ^ t h i s i s c a l l e d r e d u c t i v e quenching and r u t h e n i u m ( I I I ) i s g e n e r a t e d . of  3such quenchers a r e : Fe(CN)^  Examples  3+ 3+ Fe , Co(acac).j> Co(phen)^ , and E u ( I I I ) .  3 S i m i l a r l y (CT) R u ( b i p y ) ^  c a n g a i n an e l e c t r o n , o x i d a t i v e q u e n c h i n g , and  ruthenium w i l l be i n t h e o x i d a t i o n s t a t e ( I ) .  Examples o f t h i s t y p e o f +  quencher i n c l u d e F e ( C N ) ~ , E u ( I I ) and R u ( N H . ) t . 4  D  1 2  Cis-trans isomerization  J O  w i t h i n t h e l i g a n d has been shown t o come about as a r e s u l t o f e x c i t a t i o n 28 i n t o Raa cs ei mm ii zl aa rt i wo an v: e l e n g t h band o f a r e l a t e d ruthenium b i p y r i d i n e  complex.  R a c e m i z a t i o n i s t h e change from an o p t i c a l l y a c t i v e compound t o a 29 r a c e m i c compound o r m i x t u r e .  i i I n t h e case o f R u ( b i p y ) ^ a r a c e m i c m i x t u r e  - 3 i s the r e s u l t .  The  For m e t a l c h e l a t e  process i s also defined  as the o p p o s i t e t o r e s o l u t i o n .  complexes, where the m e t a l atom i s the o n l y c h i r a l  the mechanisms f o r r a c e m i z a t i o n can be d i v i d e d i a t i v e , and  associative.  case of a b i d e n t a t e l i g a n d , at l e a s t one The  dissociated  centre,  into d i s s o c i a t i v e , non-dissoc-  D i s s o c i a t i v e mechanisms i n c l u d e the s e p a r a t i o n  centre.  end  of one  l i g a n d , or i n  r e m a i n i n g l i g a n d s r e a r r a n g e w i t h o u t bond d i s s o c i a t i o n and l i g a n d or end  returns  i n i t i a l state.  t o the c o o r d i n a t i o n  a  sphere of the m e t a l , the  For a d e s c r i p t i o n of l i g a n d rearrangements of t h i s t y p e ,  r e f e r e n c e 30.  T h i s mechanism can be c h a r a c t e r i z e d  l e s s t h a n the energy r e q u i r e d  see  by an a c t i v a t i o n energy  t o d i s s o c i a t e one m e t a l t o l i g a n d bond.  A p o s i t i v e a c t i v a t i o n volume w h i c h a l s o c h a r a c t e r i z e sumably due  the  of t h e l i g a n d from the m e t a l  the t o t a l p r o c e s s changes the o p t i c a l a c t i v i t y to the o p p o s i t e sense t o  not  29  t o the f r e e l i g a n d , when s o l v a t e d ,  the mechanism, i s p r e -  t a k i n g up more space than  31 the c o o r d i n a t e d  ligand.  Non-dissociative  mechanisms m a i n t a i n a l l l i g a n d s  i n the  coordination  sphere of the m e t a l .  There have been proposed 3 such rearrangements or 32 t w i s t s which i n v e r t the o p t i c a l a c t i v i t y . These a r e t h e B a i l a r t w i s t , 33 34 Ray and Dutt t w i s t , and the S p r i n g e r and S i e v e r s t w i s t . See f i g u r e 1 f o r a d e s c r i p t i o n of t h e s e mechanisms. same f o r the i s o m e r s l a b e l l e d A . t h a t the Ray  and  The  The  donor atoms a r e numbered  t r a n s f o r m a t i o n s i n the f i g u r e show  D u t t mechanism does r e s u l t i n a d i f f e r e n t arrangement of  donor atoms about the m e t a l c e n t r e t h a n does the B a i l a r mechanism. the t r a n s p a i r s i n the A isomer 1-3, they a r e 1-5, 2-5, and  and  3-4.  the  2-6,  and  3-4,  2-4,  and  but a f t e r a Ray  5-6.  and  Notice  After a Bailar twist  Dutt t w i s t they are  1-6,  By f o l l o w i n g t h e s e p a i r s the f i g u r e shows t h a t the B a i l a r  S p r i n g e r S i e v e r s mechanisms a r e e x a c t l y the same, not  o n l y i n the  a r r a y of donor atoms, but a l s o i n the a r r a y of donor atoms i n the D ^  final  Figure 1  Springer  and  Sievers  - 5 proposed  intermediate.  These t w i s t mechanisms are c h a r a c t e r i z e d by an a c t i v a t i o n energy w h i c h c o u l d be l e s s t h a n the d i s s o c i a t i o n energy f o r one s m a l l a c t i v a t i o n volume. be n e g a t i v e .  end of t h e l i g a n d and by a  I n some cases the a c t i v a t i o n volume, AV^,  T h i s i s e x p l a i n e d as a D^^  can even  intermediate having a greater  a b i l i t y t o pack s o l v e n t m o l e c u l e s between the l i g a n d s than the p r o p e l l e r shaped  c o n f i g u r a t i o n s of t h e o p t i c a l isomers.  Also n o t i c e that the  inter-  m e d i a t e s of b o t h mechanisms a r e o p t i c a l l y i n a c t i v e ( i . e . have a t l e a s t 1 p l a n e of symmetry). An a s s o c i a t i v e mechanism has been i n v e s t i g a t e d t h e o r e t i c a l l y w h i c h 35 i n c l u d e s a seven c o o r d i n a t e  species.  T h i s would mean p i c k i n g up a u n i -  d e n t a t e i o n or s o l v e n t m o l e c u l e .  T h i s mechanism w i l l not be d i s c u s s e d I| l e n g t h h e r e as i t i s most u n l i k e l y f o r R u ( b i p y ) ^ • The  p e r c h l o r a t e i o n i s known t o a s s o c i a t e w i t h t h e  at  tris(bipyridine)  c h r o m i u m ( I I I ) i o n because the l u m i n e s c e n c e i s enhanced i n t h e p r e s e n c e of 36 perchlorate ions. r a t e of t h e r m a l  Thus i t i s not s u r p r i s i n g t h a t p e r c h l o r a t e a f f e c t s the  r a c e m i z a t i o n of other t r i s ( b i p y r i d i n e ) and  tris(l,10-phenan-  37 t h r o l i n e ) metal chelate ions. Photoracemizations  of m e t a l c h e l a t e complexes a r e not common.  Four +3  such r a c e m i z a t i o n s which a r e known a r e t r i s ( o x a l a t o ) c o b a l t ( I I I ) [Coiox)^ 3+  tris(l,10-phenanthroline)chromium(III)[Cr(phen),j +  line) cobalt (III) [Co(phen)^ ]^,  and  33  ]  ]  30 >  39  '  ,  tris(1,10-phenanthro-  tris(ethylenediamine)chromium(III)  3+ 41 [Cr(en)^ ] .  A l t h o u g h l u m i n e s c e n c e , r a t e , and quenching s t u d i e s have been 3+ 38 39 done on t h e r a c e m i z a t i o n of Cr(phen).j , ' the mechanism has not been 3+ | | e l u c i d a t e d . The Co(phen)^ becomes Co(phen)^ i n the presence of l i g h t and the l a b i l e C o ( I I ) r a c e m i z e s by a d i s s o c i a t i v e m e c h a n i s m . ^  +  As w i t h C r ( p h e n ) ^ ,  3+ 41 the mechanism f o r the r a c e m i z a t i o n of C r ( e n ) ^ has not been e l u c i d a t e d .  -  6 -  Thus t h e r e i s l i t t l e background to suggest c h e m i c a l r a c e m i z a t i o n of Ru(bipy)  what mechanism the photo-  would f o l l o w .  - 7 EXPERIMENTAL: T r i s ( b i p y r i d i n e ) r u t h e n i u m ( I I ) d i c h l o r i d e h e x a h y d r a t e (A) was from  G.F.  S m i t h and had been p r e v i o u s l y r e c r y s t a l l i z e d .  R e s o l u t i o n of R u ( b i p y ) ^ : 22 The method of B u r s t a l l gave low o p t i c a l y i e l d . A method s i m i l a r t o 24 -4 Dwyer and G a y a r f a s a f f o r d e d t h e b e s t r e s u l t s . 0.2926 gm (3.957 x 10 -4 moles) A and 0.1317 gm  (3.944 x 10  moles) p o t a s s i u m antimony t a r t r a t e  were d i s s o l v e d i n 5 ml of hot w a t e r .  On slow c o o l i n g t o i c e t e m p e r a t u r e  d a r k orange c r y s t a l s of ^ 1 mm d i m e n s i o n s formed.  The s o l u t i o n was vacuum  f i l t e r e d and t h e c r y s t a l s were r e c r y s t a l l i z e d i n the d a r k from 2.5 ml of water t o g i v e 85.4 mg of [ (SbO) (C .H. 0,. ] „Ru ( b i p y ) „. 4  4  b  z  From t h i s p o i n t on every-  j  t h i n g was c a r r i e d out under r e d l i g h t or i n the d a r k . dissolved  i n 20 ml of 10%  a d d i t i o n of KBr.  /v NaOH.  The R u ( b i p y ) ^  T h i s p r o d u c t was  was p r e c i p i t a t e d by  T h i s m i x t u r e was heated u n t i l d i s s o l u t i o n was  complete  and then c o o l e d s l o w l y t o g i v e f l a k e y orange c r y s t a l s w h i c h were f i l t e r e d by s u c t i o n . These were r e c r y s t a l l i z e d from a KBr s o l u t i o n . 5.47  A s o l u t i o n of  x 1 0 ~ M R u ( b i p y ) B r gave [ o ] ^ = -793 ± 8 o ! T r i s (acetylacetonato) c o b a l t ( I I I ) : 4  3  2  42 The p r e p a r a t i o n i s e s s e n t i a l l y the same as Bryant and F e r n e l i u s . s a t u r a t e d s o l u t i o n of CoC£ *6 ^ 0 2  of p o t a s s i u m c a r b o n a t e . off.  A  was poured i n t o a c o n c e n t r a t e d s o l u t i o n  The r e s u l t i n g p u r p l e c o b a l t c a r b o n a t e was  0.6 gm of t h e p u r p l e s o l i d t o g e t h e r w i t h 4 m l 2,5-pentandione  filtered were  heated on a steam b a t h t o ^90°C.  A f t e r 6 ml of 10% H ^  were added, t h e  r e a c t i o n was complete i n 2 min..  The s o l u t i o n was l e t s t a n d f o r 3 days  the green s o l i d f i l t e r e d o f f . T h i s s o l i d was r e c r y s t a l l i z e d from 42 65-110°C pet e t h e r as i n t h e r e f e r e n c e .  and  benzene/  - 8 T r i s (1,10 - p h e n a n t h r o l i n e ) c o b a l t  trichloride:  The p r e p a r a t i o n i s s i m i l a r t o V.P. P f e i f f e r and B r . Herdelmann. Cobalt (H)pe'yf* m " I ' l ^ .6 gm  0.25  gm  (1.1 mmoles) and  43  1,10-phenanthroline,  (3.1 mmoles) were heated t o g e t h e r f o r 4 hours a t 180°C, l e t c o o l t o  room temperature and d i s s o l v e d i n 15 ml o f 30% methanol.  The  resulting  m i x t u r e was g r a v i t y f i l t e r e d t o g i v e a p u r p l e s o l i d and an orange  solution.  The s o l u t i o n was b o i l e d down t o 2 ml and sodium c h l o r i d e was added u n t i l 2 phases were o b s e r v e d .  The m i x t u r e was b o i l e d down t o a t h i c k o i l and  t r a c t e d w i t h 15 ml of b o i l i n g acetone.  ex-  A f t e r decanting the acetone, the  s o l i d was heated on a steam b a t h t o remove a l l t r a c e s of acetone.  The  solid  was r e c r y s t a l l i z e d from w a t e r .  Equipment: I s o t r o p i c s p e c t r a were run on a Cary 11.  Circular dichroism spectra  were run on a J a s c o (J20) s p e c t r o m e t e r .  Luminescence  l i f e t i m e measurements:  A p p a r a t u s f o r l i f e t i m e measurements i s s i m i l a r t o t h a t of Demas and 43 Flynn.  The  gas l a s e r tube i s about 50 cm l o n g .  I t was r u n a t a p r e s -  s u r e between 110 and 125 t o r r w i t h a f l o w of n i t r o g e n c o n t r o l l e d by a n e e d l e v a l v e on the N  2  t a n k (grade G Canadian L i q u i d A i r ) and pumped from the o t h e r  end of the l a s e r tube w i t h a r o t a r y vacuum pump.  D i s c h a r g e of the c a p a c i t o r s  b u i l t onto the l a s e r tube was c o n t r o l l e d by an e x t e r n a l s p a r k gap and tion.  The N  2  plasma produces an e m i s s i o n a t 337 nm.  charged t o 12 kV by a Spellman model PN-15  0-15  thyra-  The c a p a c i t o r s were  kV h i g h v o l t a g e power s u p p l y .  The l a s e r i t s e l f i s housed i n an aluminum s c r e e n cage and removed about 3 m from the d e t e c t i o n a p p a r a t u s t o reduce e l e c t r i c a l n o i s e . a r e p r e s e n t a t i o n of the o p t i c a l paths.  See f i g u r e 2 f o r  The l a s e r p u l s e was  focused i n t o  - 9-  10.5kV Power  P. M.  Supply  Monoch ro meter  {)—O  Oscilloscope  12 kV Power Sup ply  Figure 2  L A S F *-*  R  Sample  - 10 the  sample c e l l w i t h a 5.5 cm d i a m e t e r , 10.8 cm f o c a l l e n g t h l e n s .  Perpen-  d i c u l a r t o t h e p a t h o f the l a s e r p u l s e was s e t t h e d e t e c t i o n system. N i k o n Auto 1:2 l e n s  A  o f f o c a l l e n g t h 50 mm was used t o f o c u s t h e e m i t t e d  l i g h t onto the s l i t s o f a Bausch and Lomb monochrometer ( c a t . no.  33-86-02).  The monochrometer has 5.36 mm  The  s l i t s and was always s e t a t 600 nm.  light  was d e t e c t e d by an RCA 8645 p h o t o m u l t i p l i e r (P.M.) mounted i n a bronze h o u s i n g and powered by a Kepco model ABC 1500 M D.C. to  t h e m u l t i p l i e r was about 10.5 kV.  power s u p p l y . V o l t a g e  The s i g n a l was t a k e n from the m u l t i p l i e r  t h r o u g h a low c a p a c i t a n c e c o a x i a l c a b l e system w i t h a 93  r e s i s t o r a t each  end h a v i n g an e f f e c t i v e r e s i s t a n c e of 46.5 fi. The s i g n a l was  amplified  t h r o u g h a p l u g i n u n i t 7A16 and d i s p l a y e d on a T e k t r o n i c s model 7904 o s c i l loscope.  The t r a c e was photographed w i t h a T e k t r o n i c s C-27  t i m e s e t t i n g B and f 1.9 l e n s  scope  camera;  u s i n g P o l a r o i d t y p e 47 ASA 3000 h i g h speed  film. The system was found adequate t o f o l l o w the decay of Rhodamine 6G i n e t h a n o l as l e s s t h a n 10 ns and the t i m e c o n s t a n t of the system i s t o o s m a l l to a f f e c t l i f e t i m e s over 100 ns. S o l u t i o n l i f e t i m e s were measured  i n a q u a r t z e m i s s i o n c e l l o r by e m i s s i o n  from t h e f r o n t s u r f a c e of a c y l i n d r i c a l q u a r t z s p e c t r o m e t e r c e l l .  The  cell  o r i e n t a t i o n f o r t h e second case was such t h a t t h e r e f l e c t e d beam t r a v e l led  between t h e d e t e c t i o n system and t h e e x c i t a t i o n p u l s e p a t h towards p o i n t  P, see f i g u r e 2. the  A C o r n i n g CS3-71-1.53 mm U.V.  sample c e l l and t h e N i k o n l e n s .  c u t o f f f i l t e r was used  between  No d i f f e r e n c e was d e t e c t a b l e i n the  l i f e t i m e of Rhodamine 6G by the two d i f f e r e n t  arrangements.  Actinometry: P o t a s s i u m f e r r i o x a l a t e a c t i n o m e t r y was c a r r i e d out as d e s c r i b e d i n " P h o t o c h e m i s t r y " b y C a l v e r t and P i t t s . ^  I n subdued l i g h t , t o each of 2  - 11 i d e n t i c a l q u a r t z c e l l s was Each c e l l was  d e l i v e r e d 3 ml of the .006 M K^FeCC^O^)^ s o l u t i o n .  capped w i t h a s m a l l magnetic s t i r r e r i n s i d e . The  t r e a t e d e x a c t l y the same except t h a t one was p l a c e of a p h o t o r a c e m i z a t i o n  c e l l s were  s e t i n the o p t i c a l t r a i n i n  s o l u t i o n f o r a measured l e n g t h of time.  t r a n s m i t t e d l i g h t was measured by a power meter, w i t h and w i t h o u t present.  Each c e l l was  then emptied i n t o a 25 ml v o l u m e t r i c  f l a s k a g a i n i n subdued l i g h t .  Each c e l l was  The  the  cell  actinometry  r i n s e d w i t h 2 ml of the  .1%  1 , 1 0 - p h e n a n t h r o l i n e s o l u t i o n , 1.5 ml of the NaOAc/H^SO^ b u f f e r s o l u t i o n , 3 ml o f d i s t i l l e d w a t e r . responding  The r i n s i n g s were s u c c e s s i v e l y added t o the c o r -  volumetric flask.  The  f l a s k s were f i l l e d  water and l e f t t o d e v e l o p f o r 1 h r . measured on a Cary 17 at 510 nm. was  a l s o measured a t 457.9  t o the mark w i t h  The  a b s o r p t i o n of the f e r r i o x a l a t e s o l u t i o n  nm.  run:  D i s t i l l e d water or a s o l u t i o n of the a p p r o p r i a t e quencher, w i t h  Ru(bipy>  p l a c e d i n a 1 cm spectrometer  as t h e d i b r o m i d e s a l t was  3  d e n s i t y o f the s o l u t i o n was s o l u t i o n was  tube, and  3  finally  s o l u t i o n was  2  The  optical The (see pass-  and H S 0 ^ towers, NaOH/calcium s u l f a t e d r y i n g 2  bubbled t h r o u g h d i s t i l l e d  d e l i v e r e d i n t o a spectrometer  c e l l was  chiral  p r e v i o u s l y p u r i f e d by  water t o h u m i d i f y  the argon.  The  c e l l w h i c h had been swept out w i t h  f l o w i n g argon and c o n t a i n e d a s m a l l magnetic s t i r b a r . spectrometer  a t 450 nm.  f l a s k of a Z w i c k l e f l a s k  argon was  ionic  the s o l i d  added and d i s s o l v e d u n t i l the  then p l a c e d i n the d e g a s s i n g  t h r o u g h Zn/ECH, C r ( N 0 >  c e l l and  n e a r but d i d not exceed 1.2  f i g u r e 3) and degassed w i t h argon. ing  distilled  The a b s o r p t i o n of the two s o l u t i o n s was  Sample p r e p a r a t i o n and r a c e m i z a t i o n  s t r e n g t h a d j u s t e d , was  and  The a d a p t e r  t o the  s h o r t e r than t h a t shown i n f i g u r e 3 so t h a t i t c o u l d  be accommodated i n t h e sample compartment o f the J a s c o  (J-20).  After closing  - 12 as  t h e lower s t o p c o c k s , t h e #5 o - r i n g j o i n t was d i s s e m b l e d CD s p e c t r a were r e c o r d e d .  The s o l u t i o n was s t i r r e d and p l a c e d i n t h e beam  of an argon i o n l a s e r tuned t o 457.9 nm. w i t h a stopwatch  and t h e i s o t r o p i c and  The time i n t h e beam was measured  and t h e power of t h e beam was measured w i t h and w i t h o u t  the c e l l present.  The CD a b s o r p t i o n a t 470 nm was r e c o r d e d .  v a l u e s were t a k e n t o determine  the r a t e of the racemization.  Successive A f t e r the race-  m i z a t i o n had proceeded s i g n i f i c a n t l y t h e i s o t r o p i c spectrum was r e c o r d e d again.  Where p o s s i b l e t h e same s o l u t i o n was then used f o r l i f e t i m e s t u d i e s  i n t h e f r o n t s u r f a c e arrangement. Temperature c o n t r o l l e d  photoracemization:  A sample, p r e p a r e d as d e s c r i b e d b e f o r e , was p l a c e d i n a d i s t i l l e d water thermostatic bath.  The t h e r m o s t a t i c b a t h was s t a i n l e s s s t e e l w i t h a vacuum  j a c k e t and double q u a r t z windows f r o n t and r e a r and on each s i d e .  The water  was c i r c u l a t e d by a Monostat C o r p o r a t i o n p e r i s t a l t i c pump through a 10 f t . copper c o i l .  A l l tygon l i n e s c o n n e c t i n g pump, c o i l , and b a t h were i n s u l a t e d  w i t h foam t u b i n g .  The copper c o i l was p l a c e d i n a l a r g e Dewar f l a s k w i t h an  i c e b a t h f o r below room temperature  runs and i n a t h e r m o s t a t t e d b a t h ( c a t .  no. 66600) from P r e c i s i o n S c i e n t i f i c f o r above room temperature l a s e r was f o c u s e d by a l e n s window.  The c e l l was s t i r r e d m a g n e t i c a l l y from underneath.  intensity.  The  o f f o c a l l e n g t h 20 cm a t t a c h e d t o t h e f r o n t  was c a r r i e d out i n s i d e t h e temperature the l i g h t  runs.  Actinometry  c o n t r o l l e d b a t h t o measure a c c u r a t e l y  Figure 3  - 14 RESULTS AND  DISCUSSION:  Photoracemization: While e x p l o r i n g the p o s s i b i l i t y of s t e r e o s p e c i f i c photochemistry  of  I|  A-Ru(bipy)  3  , we have e s t a b l i s h e d t h a t i t s CD spectrum d e c r e a s e s on exposure  t o l i g h t w i t h no c o r r e s p o n d i n g  r e d u c t i o n of t h e i s o t r o p i c spectrum.  I t has  been noted by Van Houten and W a t t s , t h a t t h i s m o l e c u l e i s extremely —  s t a b l e a t room temperature i n degassed s o l u t i o n (<j> < 10  5  photo-  8 ).  The  photorace-  m i z a t i o n c o u l d be f o l l o w e d q u a n t i t a t i v e l y by t h e l i n e a r dependence o f t h e l o g a r i t h m o f t h e d i f f e r e n t i a l a b s o r p t i o n a t 470 nm on i n t e g r a t e d absorbed intensity: ln  -4= A o  klt a  The t h e o r e t i c a l b a s i s f o r t h i s f o r m u l a t i o n i s d i s c u s s e d i n a l a t e r s e c t i o n , and d e r i v e d i n d e t a i l i n Appendix A, where t h e c o n s t a n t  k i s r e l a t e d to the  r a c e m i z a t i o n quantum y i e l d . S i n c e t h e quantum y i e l d f o r r a c e m i z a t i o n , e r a t u r e i s v e r y s m a l l (<J>  1T3-C  = 2.9 x 10  -4  < r  r  a  c  »  i n  water a t room temp-  ), i t f o l l o w s that the e l e c t r o n i c a l l y  e x c i t e d s p e c i e s t h r o u g h w h i c h t h e r a c e m i z a t i o n o c c u r s must be a c h i r a l  species  i f formed i n h i g h y i e l d , but c o u l d be a c h i r a l i f formed o n l y i n t h e same y i e l d as t h e r a c e m i z a t i o n i t s e l f .  I n a sense b o t h of these s t a t e m e n t s a r e  t r u e i n t h i s system, as we s h a l l i n d i c a t e i n t h e subsequent development.  Quenching e f f e c t s : I|  There i s a l o n g - l i v e d s t a t e f o r R u C b i p y ) ^ , w i t h T = 0.6 ysec w h i c h i s r e s p o n s i b l e d i r e c t l y f o r t h e i n t e n s e phosphorescence o f t h i s m o l e c u l e . r o l e of that s t a t e i n the photoracemization  The  was e x p l o r e d by s t u d i e s of b o t h  l u m i n e s c e n c e and r a c e m i z a t i o n quenching under comparable c o n d i t i o n s .  In  - 15 a d d i t i o n , i t was hoped t o e s t a b l i s h whether o r n o t Ru(I) o r R u ( I I I )  species  t a k e p a r t t o any a p p r e c i a b l e e x t e n t i n t h e r a c e m i z a t i o n by u s i n g s u i t a b l e quenchers w h i c h a c t as e l e c t r o n donors o r e l e c t r o n a c c e p t o r s . The  quenching of phosphorescence was f o l l o w e d by measuring l i f e t i m e s  from o s c i l l o s c o p e d i s p l a y s o f t h e phosphorescence decay.  The d a t a were  fit-  ted t o : ln I - l n I = o  -t/x  I n every case t h e d a t a p l o t t e d as l n I ( i n t e n s i t y ) a g a i n s t t i m e t gave straight lines.  The b a s e l i n e f o r t h e d i s p l a y s was c a r e f u l l y e s t a b l i s h e d ,  however, an e r r o r o f o n l y 5% i n t h e p o s i t i o n o f t h e b a s e l i n e r e s u l t e d i n a noticeable curvature i n the plot. Racemization were e x p l o r e d .  quantum y i e l d s i n t h e presence of v a r i o u s i o n i c quenchers  The d a t a w i t h FeC£„, K.Fe(CN), and Co(phen) C£ 0  5  H  D  h e r e as examples o f e l e c t r o n t r a n s f e r quenchers.  5  0  are discussed  5  I n each o f these  cases,  however, t h e i o n i c s t r e n g t h dependence i s enormous, so t h a t , even though we have t r i e d t o u s e t h e same c o n d i t i o n s as p r e v i o u s work i n t h e l i t e r a t u r e , the agreement w i t h l i t e r a t u r e quenching d a t a i s not v e r y good. FeC£.j quenching ( e l e c t r o n a c c e p t o r ) was c a r r i e d out i n 0.10 M-NaC&O^ and  0.01 M-HC&O^ t o correspond -3 t r a t i o n o f 3.0 x 10 M gave:  w i t h t h a t i n r e f e r e n c e 14. Quencher concen-4 <j> = 3.0 x 10 and T = 250 nsec. A c o r X"3 C  r e c t i o n f o r t h e p e r c h l o r a t e i o n e f f e c t ( s e e l a t e r d i s c u s s i o n ) reduces <l>  £  -4 t o 2.3 x 10  .  The e x t e n t o f quenching o f t h e r a c e m i z a t i o n i s somewhat  l a r g e r than that of t h e luminescence l i f e t i m e , n e v e r t h e l e s s , the r a c e m i z a t i o n quantum y i e l d i s l e s s t h a n i n w a t e r .  S i m i l a r r e s u l t s were o b t a i n e d w i t h t h e 3+ -3 o t h e r e l e c t r o n a c c e p t o r quenching m o l e c u l e , Co(phen)^ . W i t h 4 x 10 3+ -4 M-Co(phen). and 0.5 M-NaC£, t}> = 1.5 x 10 and T = 236 n s e c . I n t h i s 3 rac c a s e , t h e r a c e m i z a t i o n has been quenched by c a . 50%, w h i l e t h e l i f e t i m e has  - 16 been reduced t o 36% o f i t s v a l u e i n water.  Although  there i s the complica-  t i o n of a l a r g e i o n i c s t r e n g t h e f f e c t , i t i s apparent t h a t t h e r e i s no e f f e c t 3+  of a c c e l e r a t i o n o f t h e r a c e m i z a t i o n v i a t r a n s i e n t f o r m a t i o n o f R u ( b i p y ) -3 4W i t h 2.0 x 10 M-Fe(CN),, , w h i c h i s an e l e c t r o n donor quencher, o  3  ,  and 0.5 M-NaCil, t h e r e i s not o n l y t h e problem o f i o n i c s t r e n g t h e f f e c t s , but 13  a l s o t h a t c o n s i d e r a b l e i o n p a i r f o r m a t i o n may o c c u r .  The v a l u e s o f <J> = rac  J  -4 2.0 x 10  and x = 263 nsec i n d i c a t e comparable quenching o f t h e two p r o c e s s e s .  T h i s system i s a l s o c o m p l i c a t e d by a permanent t h e r m a l r e a c t i o n d e s t r o y i n g Ru(bipy)  3  .  A l l of t h e s e data i n d i c a t e t h a t n e i t h e r Ru(I) nor R u ( I I I ) s p e c i e s p l a y an i m p o r t a n t  part i n the racemization.  From t h e i n t e n s i t y we have used and  the quantum y i e l d o f quenching, t h e t r a n s i e n t c o n c e n t r a t i o n s of R u ( I ) , p r o 13 45 posed by Demas and A d d i n g t o n and o f R u ( I I I ) proposed by L i n and S u t i n , —8 a r e c a l c u l a t e d t o be c a . 10 M and t h e r e f o r e would have a h a l f l i f e o f 10 3+  msec (compare r e f . 1 3 ) . I t i s known t h a t R u ( b i p y ) ^  i skinetically  relatively 24  i n e r t and i s u n l i k e l y t o i s o m e r i z e t o any e x t e n t i n times o f t h i s o r d e r . For a n e u t r a l quencher, b o t h i o n i c s t r e n g t h and i o n - p a i r i n g problems are e l i m i n a t e d .  Co(acac)  i s such a s u i t a b l e quencher, w i t h a quenching •^8 —1 —1 12 r a t e c o n s t a n t of 6.7 x 10 M sec . I t s action i s said to involve 3  3+  e l e c t r o n t r a n s f e r t o t h e c o b a l t e n t i t y r e s u l t i n g i n C o ( I I ) and R u ( b i p y ) ^ 46 transient species.  We have c o n f i r m e d  t h e v a l u e o f t h e quenching c o n s t a n t -3 by our l i f e t i m e measurements: 3.3 x 10 M - C o ( a c a c ) reduces t h e l u m i n e s c e n c e g l i f e t i m e t o 222 ns from i t s v a l u e o f 657 ns i n w a t e r . Thus k = 9.0 x 10 q -1 -1 M s At t h e same c o n c e n t r a t i o n of Co(acac)„, t h e v a l u e o f d> i s reduced 3 rac -4 3  t o 1.3 x 10  , 45% o f i t s v a l u e i n t h e absence o f quencher. 8  to  = 5.7 x 10  —1 M  the p h o t o r a c e m i z a t i o n  This  corresponds  —1 s  .  I t i s therefore reasonably w e l l e s t a b l i s h e d that  o c c u r s v i a t h e same e l e c t r o n i c s t a t e as t h a t r e s p o n s i b l e  - 17 3  2+  f o r t h e l u m i n e s c e n c e , namely, t h e (CT) R u ( b i p y ) ^ . T h i s s t a t e i s known t o be formed w i t h near u n i t quantum y i e l d , hence i t i s t h e s t a t e w h i c h r e t a i n s the c h i r a l i t y o f t h e ground s t a t e t h r o u g h e x c i t a t i o n and d e e x c i t a t i o n , except f o r t h a t s m a l l p a r t w h i c h undergoes r a c e m i z a t i o n . E f f e c t of D 0: 2  S u b s t i t u t i o n o f D 0 f o r H 0 i s known t o i n c r e a s e b o t h t h e quantum y i e l d 2  2  2+ and t h e l i f e t i m e o f l u m i n e s c e n c e o f R u ( b i p y ) ^  • We have c o n f i r m e d  this  effect  by l i f e t i m e measurements (see T a b l e I) and have a l s o determined t h e quantum y i e l d s f o r r a c e m i z a t i o n i n the two s o l v e n t s .  The r a t i o o f  A ^ ^ / A ^ O  = 1.83  rac r a c i s t h e same, w i t h i n e x p e r i m e n t a l  e r r o r a s the r a t i o Table I H 0  D 0  2  +  [Ru(bipy)^ ]  rac x/ns */*o x/t  The  o  2  8.5x10" 2.9xl0~  *  T ^ ^ / T ^ ^ .  4  5  7. 4x10 5.3x10  657  1166  1  1.83  1  1.77  -5 -4  l o g i c a l c o n c l u s i o n from t h e s e d a t a i s a g a i n t h a t t h e s t a t e l e a d i n g t o  phosphorescence and t h a t i n v o l v e d i n t h e r a c e m i z a t i o n a r e one and t h e same, the  3  (CT) .  E f f e c t of perchorate The  ion:  quantum y i e l d f o r r a c e m i z a t i o n i n the p r e s e n c e o f 0.20 M NaCdO^ i s  i n c r e a s e d o v e r t h a t i n water by a f a c t o r o f 1.46. U n l i k e t h e c a s e o f D 0 2  as s o l v e n t , however, t h e l i f e t i m e i s v i r t u a l l y u n a f f e c t e d by the p r e s e n c e °  f  C  T  *°4~' C £ 0 4  / T  H 0 2  =  9 2  °- '  - 18 A c c e l e r a t i o n of the r a c e m i z a t i o n i s u n u s u a l .  In thermal  racemizations,  9 CJIO^  r e t a r d s the i n v e r s i o n .  In t h i s c a s e , t h e r e i s v e r y l i t t l e e f f e c t  the photophysical processes, according to x. c o n c l u s i o n t o be reached  Perhaps t h e o n l y  concrete  i s t h a t some a s s o c i a t i o n o c c u r s between m e t a l w i t h CW^  complexes of b i p y r i d i n e and 1,10-phenanthroline  on  chelate  ions.  Temperature dependence:  3 S i n c e o n l y one i n about 4000 (CT)  2+ Ru(bipy)^  molecules  s i o n t o the o p p o s i t e s t e r e o i s o m e r a t room t e m p e r a t u r e , a b l e energy b a r r i e r t o i n v e r s i o n i n the t r i p l e t  state.  undergoes i n v e r -  t h e r e must be a c o n s i d e r We have measured  t h i s energy b a r r i e r d i r e c t l y by f o l l o w i n g the temperature dependence of <j> T03.C  Q u a l i t a t i v e l y , we n o t e t h a t the l i f e t i m e i t s e l f decreases  with increasing g  temperature,  as has been examined i n d e t a i l by Van Houten and Watts  and  9 by W a t t s , H a r r i n g t o n and Van Houten.  However, the quantum y i e l d f o r r a c e -  m i z a t i o n i n c r e a s e s f a s t e r w i t h i n c r e a s i n g t e m p e r a t u r e than does the I t i s not known whether the r e a c t i o n o c c u r s v i a an a c h i r a l w i t h i n the t r i p l e t  manifold:  T"'.  intermediate  2+  o r by a p r o c e s s t h a t i n v o l v e s s i m u l t a n e o u s  2+  d e e x c i t a t i o n t o the ground s t a t e :  ->- A-Ru(bipy)  2+  In e i t h e r case, the energy of a c t i v a t i o n f o r i n v e r s i o n w i l l g i v e u s e f u l i n f o r m a t i o n about the mechanism o f r a c e m i z a t i o n .  - 19 Table I I Temp/°C  K/T  x/ns l n ( - )  37.0  -3 3. 23x10"  507  14 .49  23.0  -3 3. 36x10"  657  14 .24  15.6  •3 3.47x10*  677  14 .21  11.0  -3 3. 52x10*  690  14 .19  To a n a l y z e t h e d a t a , we have determined t h e apparent energy of a c t i v a t i o n associated w i t h the l i f e t i m e .  The d a t a i n T a b l e I I , when f i t t e d t o an A r r h e n i u s  e q u a t i o n o f t h e form: -ln x = g i v e , f o r our d a t a :  E ( x ) = 2.10 k c a l / m o l e and A ( x ) = 5.71 x 10 ' s \  f o r Van Houten and Watts s  + l n A(x)  8  data:  and,  E ( x ) = 1.81 k c a l / m o l e and A ( x ) = 3.57 x 10  7  , f o r t h e t e m p e r a t u r e range from 5° t o 40°C, see f i g u r e 4. 9 I n t h e paper by W a t t s , H a r r i n g t o n and Van Houten,  t h e temperature  dependence over a much l a r g e r range was f i t t e d t o a more c o m p l i c a t e d e q u a t i o n . S i n c e our r a c e m i z a t i o n d a t a extend o n l y over a s m a l l range of t e m p e r a t u r e , t h i s d e t a i l e d a treatment i s unnecessary.  However, E ( x ) has no r e a l s i g n i f i -  cance i n terms o f t h e mechanism; i t i s an apparent a c t i v a t i o n energy. complete t r e a t m e n t i s g i v e n i n Appendix  A more  B.  When t h e r a c e m i z a t i o n d a t a a r e f i t t e d t o a s i m i l a r e q u a t i o n , t h e r e r e s u l t s , see f i g u r e 5,:  E ( r a c ) = 13.9 k c a l / m o l e and A ( r a c ) = 5.0 x 10^ s ^. Table I I I  Temp/°C 3.0  K/T  ^  3.62xl0"  3  I n * ^  .0000521  -9.96  _ 3  .000288  -8.15  3  .000933  -6.98  23.0  3.38xl0  40.0  3.19xl0~  Figure 4  - 20 -  mlvs.1 r  —:  T  14.5  • from reference S * from Table IT  14.4 T  ml 14.3 +  14.2  14.1 3  -2  3.3  3.4 1  «  - 22 A g a i n , t h i s i s an apparent a c t i v a t i o n energy whose meaning i s examined i n the f o l l o w i n g  section.  Mechanism: From the e x p e r i m e n t s done we know t h e mechanism must i n c l u d e every mo 3  3  c u l e p a s s i n g t h r o u g h t h e (CT)  s t a t e , t h e (CT)  a t h e r m a l a c t i v a t i o n energy must be a s s o c i a t e d  s t a t e must be c h i r a l , and with the ultimate  C o n s i d e r t h e f o l l o w i n g network: Figure 6  rac  k„ + k„ + k. £•  5  H  From t h e v a l u e s o f <j> we know k,<<k„ + k„. rac 4 2 3  k  0  1  + k^ + k j  '  Therefore:  inversion  - 23 and  eliminating  +  k^:  rac  4  B o t h k^ and x have the t e m p e r a t u r e dependences:  ~I4_ k, = A. e 4 4  RT -E(T)  x-  K t \ - A(x)  1  R  e  T  Thus E(T)  VU  ln+  - *n /(__^  "  E  4  RT The  apparent E ( r a c ) from the p r e v i o u s s e c t i o n i s t h e r e f o r e : E ( r a c ) = E(x) - E. 4  and  hence E. = 16.0 4  Similarly A  4  = 2.90  x 10  1 4  kcal/mole  1  sec" .  By a p p l y i n g t h i s model t o our d a t a we c a l c u l a t e a t r u e a c t i v a t i o n Cj  energy f o r r a c e m i z a t i o n of 16.0  kcal/mole.  shows an a c t i v a t i o n energy of 16.02 of a photo product  kcal/mole  Ru(bipy)  3  tures.  They suggest t h a t t h e photo product  ended b i p y r i d i n e l i g a n d .  The work of Van Houten et a l 3 f o r p r o d u c t i o n from  (CT)  i n s t r o n g l y a c i d s o l u t i o n s a t e l e v a t e d temperai s a Ru(II) species with a  I f t h i s i s the c a s e ,  one-  i t provides evidence that  r a c e m i z a t i o n proceeds t h r o u g h a d i s s o c i a t i v e mechanism.  - 24 Selective  Photochemistry:  S e l e c t i v e quenching due t o o p t i c a l a c t i v i t y has been observed  before i n  47 o r g a n i c systems.  We  d e c i d e d t o study s e l e c t i v e p h o t o c h e m i s t r y  r e s u l t from c h i r o s e l e c t i v e l u m i n e s c e n c e quenching. t i o n s are necessary  f o r such a s t u d y .  The  d i f f u s i o n c o n t r o l l e d to a l l o w s e l e c t i v i t y .  s t a b l e to racemization.  A number of  specifica-  quenching must be s l o w e r  than  For the r e s u l t i n g o p t i c a l  t o be measurable the quencher o r i t s p h o t o c h e m i c a l and p h o t o c h e m i c a l l y  which could  activity  product must be t h e r m a l l y  The v a l u e s of E  s u f f i c i e n t l y d i f f e r e n t t o a f f o r d measurement of e n a n t i o m e r i c  and  e  must be  excess p r e f e r -  I [  a b l y a t a w a v e l e n g t h where R u ( b i p y ) ^ does not absorb. 3+ | | Co(phen)^ , a l t h o u g h c h i r a l , g i v e s Co(phen)^ i n the p r e s e n c e of 40 w h i c h s e t s up a c h a i n r e a c t i o n of r a c e m i z a t i o n . necessary  criteria.  by R u ( b i p y ) ^  C o ( a c a c ) ^ f i l l s a l l the  I t has a l s o been shown t h a t C o ( a c a c ) ^ , when s e n s i t i z e d  does undergo p h o t o c h e m i c a l  change.  Indeed t h i s quenching by C o ( a c a c ) ^ does show a s e l e c t i v i t y . photoracemization C o ( a c a c ) ^ appears.  light  During  i n the p r e s e n c e o f t h i s quencher, the CD spectrum of The  s p e c t r a i n f i g u r e 7 show the growth w i t h i n c r e a s i n g  i r r a d i a t i o n time of the. CD a b s o r p t i o n i n the r e g i o n of 550-720 nm.  This  CD  spectrum i s c l e a r l y i d e n t i f i e d w i t h t h a t of C o ( a c a c ) ^ not o n l y by i t s g e n e r a l shape, but more i m p o r t a n t l y , by t h e p o i n t of z e r o d i f f e r e n t i a l a b s o r p t i o n a t 48 about 622 nm g i v e n by Jonas and Norden. A c c o r d i n g t o the a b s o l u t e c o n f i g u r a t i o n assignment of M c C a f f e r y , 49 and Norman  Mason  ++ the R u ( b i p y ) ^  we used i s A or r i g h t handed screw h e l i x .  Sim-  i l a r l y the r e s u l t i n g excess of the C o ( a c a c ) ^ isomer i s a l s o A a c c o r d i n g t o the assignment of Jonas and Norden."^  The  i n t e r a c t i o n of t h e  (CT)^RuCbipy)"^  w i t h C o ( a c a c ) ^ c o u l d e i t h e r cause s e n s i t i z e d r a c e m i z a t i o n o r d i s s o c i a t i o n o f 3 | | the Co isomer w h i c h p r e f e r e n t i a l l y r e a c t s w i t h (CT) R u ( b i p y ) ^ . Meyerstein  Figure 7  wavelength  I  550  I  1 I  baseiin  /  in nm  I  I  600  1 I 1/  /  /  CD spectrum o f Co(acac).j from r e f . 48. E v o l u t i o n of CD spectrum of Co(acac), p h o t o s e n s i t i z e d by A-Ru(bipy)^2+ #  - 26 -  et a l  46  r e f e r t o p h o t o r e d u c t i o n and d e c o m p o s i t i o n of t h e CoCacac)^.  Their  <j)'s show t h a t p r o d u c t i o n of C o ( I I ) i s p r i m a r i l y due t o s e n s i t i z a t i o n by  (CT)  3  I [  Ru(bipy)^  r a t h e r than by d i r e c t a b s o r p t i o n .  The p r o d u c t i o n of a C o ( a c a c )  3  3 CD spectrum  a t a l l , p o i n t s once a g a i n to r e t e n t i o n o f c h i r a l i t y by t h e  I j  Ru(bipy)  3  .  The g e n e r a t i o n of the spectrum  of the A isomer of C o ( a c a c )  (CT) 3  I |  shows a p r e f e r r e d i n t e r a c t i o n between A C o ( a c a c ) to d e s t r u c t i o n of the  3  and A R u ( b i p y )  3  leading  former.  F i g u r e 8 shows q u a n t i t a t i v e l y t h e growth of the e n a n t i o m e r i c excess of the Co(acac).j. of t h e quenching  From i n t i a l r a t e s , an e s t i m a t e of the o p t i c a l  i n t e r a c t i o n shows the r a t e o f growth of A C o ( a c a c )  of t h e r a t e of d e s t r u c t i o n o f Co(acac).j. A Ru(bipy)  3  3  i s 14%  D u r i n g t h e same f i r s t 2 m i n u t e s t h e  l o s t 13% of i t s i n i t i a l o p t i c a l a c t i v i t y .  i n the quenching  selectivity  p r o c e s s i s g r e a t e r t h a n 14%.  Thus the  selectivity  On a molar b a s i s , however, t h e I |  a c t i v i t y g e n e r a t e d i n the C o ( a c a c ) frUP exceeds t h a t l o s t by the R u ( b i p y ) ^ because of the s m a l l i> of t h e l a t t e r . rac 3  I n a survey of t h e r m a l e l e c t r o n t r a n s f e r r e a c t i o n s , n o e v i d e n c e c o u l d be found f o r any c h i r o s e l e c t i v e p r o c e s s e s .  Pffure  8  Concentration  vs.  time  a [Co(acac) ] 3  5  +  t  [ARu(bipy) ] - [ A R ( b i p y ) ] 3  ®[ACo(acac)  u  3  3  ]-[ACo(acac) ] 3  - 28 Conclusions: 1.  From  <r  a n a r  a  d i f f e r e n t i a l quenching s t u d i e s we have e s t a b l i s h e d t h a t  c  3 (CT) R u ( b i p y ) 2.  is chiral.  There i s o p t i c a l s e l e c t i v i t y i n the quenching p r o c e s s of  3.  4+ 3  for deactivation  (CT^RuOjipy)^.  There i s e v i d e n c e t h a t the r a c e m i z a t i o n o c c u r s v i a a d i s s o c i a t i v e  Differential  process.  quenching e f f e c t s of o p t i c a l isomers s h o u l d not have been  an unexpected e f f e c t .  N a t u r a l p h o t o c h e m i c a l r e a c t i o n s have been shown to S  occur  5i  w i t h o p t i c a l l y a c t i v e m a t e r i a l s such as rhodop^in pigments  and  chloro-  52 phyll.  The mechanism by w h i c h e x c i t a t i o n energy of r h o d o p i n  to the nervous system may fer.  i s transferred  i n v o l v e c h i r o s e l e c t i v e energy and/or e l e c t r o n t r a n s -  S i m i l a r l y t h i s c o u l d be the case f o r antenna c h l o r o p h y l l . Differential  quenching and  an e f f e c t i v e s y n t h e t i c t o o l .  s e n s i t i z a t i o n of o p t i c a l isomers c o u l d  I f a c h i r a l cage s t r u c t u r e of p y r i d i n e l i g a n d  c o u l d be made f o r R u ( I I ) i n such a way racemize,  be  that the Ru(II) species could  a g r e a t e r r e s o l u t i o n c o u l d be a c h i e v e d  for Co(acac) . 3  We  not showed  14% s e l e c t i v i t y where a r e c e n t r e s o l u t i o n by p a r t i t i o n i n g between c h i r a l 53 s o l v e n t s showed 5-8%  optical  yield.  Another c h i r a l quencher Co(EDTA) than Co(acac),j.  would l i k e l y have g r e a t e r  I n low i o n i c s t r e n g t h , i o n p a i r i n g f a v o u r s  solubility  increased  I [  quenching and t h u s l e s s r a c e m i z a t i o n of R u ( b i p y ) ^ show even g r e a t e r s e l e c t i v i t y i n  .  T h i s quencher c o u l d  photochemistry.  F u r t h e r i n v e s t i g a t i o n of the mechanism of r a c e m i z a t i o n s h o u l d determination  of the a c t i v a t i o n volume and pH e f f e c t s .  The  s h o u l d be l a r g e and p o s i t i v e f o r a d i s s o c i a t i v e mechanism. the r a c e m i z a t i o n s h o u l d be enhanced by l e n g t h e n i n g t i v e i n t e r m e d i a t e t o the  racemization.  include  a c t i v a t i o n volume In a c i d s o l u t i o n  the l i f e o f the d i s s o c i a -  - 29 I f f l a s h p h o t o l y s i s u s i n g a c i r c u l a r l y p o l a r i z e d a n a l y s i n g beam c o u l d be p e r f e c t e d , o b s e r v a t i o n o f some i n t e r m e d i a t e s i n t h e mechanism c o u l d be possible.  T h i s c o u l d d i s t i n g u i s h between t h e p o s s i b l e r e a c t i o n s : 3  A(CT) Ru(bipy)^  +  3  + A (CT) R u ( b i p y ) ^ "  or 3  A(CT) Ru(bipy)^ (labelled  +  1  -> ARu(bipy)^ "  i n f i g u r e 6).  In g e n e r a l , the r o l e of o p t i c a l a c t i v i t y i n the p h o t o p h y s i c a l processes of R u ( b i p y ) ^ effects.  has been i g n o r e d .  We have shown t h a t t h i s c a n have s i g n i f i c a n t  APPENDIX A - K i n e t i c A n a l y s i s of R a c e m i z a t i o n For each r a c e m i z a t i o n r u n d i f f e r e n t i a l absorbances  of c i r c u l a r l y p o l a r -  i z e d l i g h t were r e c o r d e d c o r r e s p o n d i n g t o d i f f e r e n t t i m e s of i l l u m i n a t i o n . The f o l l o w i n g s i m p l i f i e d mechanism was u t i l i z e d for. d a t a r e d u c t i o n :  A RuCbipy)^  +  1  A RuCbipy)^ c^AA' which c o r r e s p o n d s t o r a t e R^,  ACRubipy)^  (A)  A RuCbipy)^  (B)  i s d e f i n e d i n t h i s case a s :  I| moles o f A R u C b i p y ) ^ produced AA cj>^  | | from A R u ( b i p y ) ^  moles of hv absorbed by A RuCbipy)*" " 1  i s d e f i n e d s i m i l a r l y f o r r e a c t i o n (B) . R  R  l " 2  «AA  = *  The r a t e s and  ' ' tfi's  are related:  ^  (  I  A A  2  )  (3)  A  where 1^ and 1^ a r e the i n t e n s i t i e s of l i g h t absorbed by the two  isomers.  The r a t e of f o r m a t i o n and d e s t r u c t i o n of each isomer can be deduced a s :  .  S i n c e <|> ^ must by symmetry e q u a l  ^  r  - *  4  A 4  I*  (5,  ct^  dARuCbipy)^  =  dARu(bip )^  m  y  ^  +  ^  (  I  ( I  A  A  _ A r  _  }  l A )  ( f i )  ( ? )  Due t o t h e n a t u r e of t h e phenomena, o n l y the d i f f e r e n c e i n c o n c e n t r a t i o n of A and A isomers i s measured i n CD s p e c t r o s c o p y .  The q u a n t i t y of i n t e r e s t  - 31 is  then: d(ARu(bipyK  - ARu(bipy)„ )  , A  A  1^ and 1^ a r e d e f i n e d i n a m i x t u r e as:  3-A  [ARu(bipy)^ ] l a  =  ( g ) 1  [ARu(bipy)^"] +  tARuCbipy)^ "] -H-  where l a i s the t o t a l l i g h t absorbed ing  by b o t h R u ( b i p y ) ^  isomers.  Substitut-  i n (8) g i v e s : d [ARu(bipy)  3  ] - [ARu(bipy)  ]  3  <fr, 2Ia( [ A R u ( b i p y K  =  ] - [ARu(bipyK  A  dt  [ARu(bipy)  So as t o a c e r t a i n <j>^^ from t h e observed  ] +  3  [ARu(bipy)  ] 3  time dependence t h e above e x p r e s s i o n  (10) i s i n t e g r a t e d t o g i v e :  ([ARu(bipy)t*l - [ A R u ( b i p y ) ^ ] )  £ n  4  ( [ A R u ( b i p y ) ^ " ] - [ARu(bipy)3  In  t  ])  ?^AA^  =  [ARu(bipy)^'] +  Q  (11) f  [ARu(bipy) ~ ] 3  our i n i t i a l c o n d i t i o n s we have a t t = 0: [AR"(bipy)£j [ARutbipy)^] +  o  =  ( 1 2 )  H  [ARu(bipy) '] 3  and +  [ARu(bipy)^ ] [ARu(bipy) ^"] + 3  =  x  ( 1 3 )  +  [ARu(bipy)^ ]  Thus t h e i n i t i a l CD a b s o r p t i o n a t 470 nm, A^ - A^, i s taken as ( [ A R u ( b i p y ) I |  [ARu(bipy)  3  | j  ] ) ^ . S u c c e s s i v e v a l u e s of ( [ A R u ( b i p y )  3  3  ]•  | |  ] - [ARu(bipy)  3  ])  f c  are  then s i m p l y t h e s u c c e s s i v e CD a b s o r p t i o n v a l u e s a f t e r i r r a d i a t i o n time t , i . e . (A^ - A ) . . R  J  (J>^ was c a l c u l a t e d from t h e s l o p e o f :  i n -^L ( A  L -  ^ - t vs. t  Vo  - 32 (or l a t i f l a changed during a run).  Total ruthenium species present was  calculated using the volume of the c e l l and the isotropic extinction coefI| f i c i e n t for Ru(bipy) at 450 nm. 3  m  =  The slope i s then: H»AA 21a A  where V = .0030 l i t r e s , Einsteins/sec,  /E  450 450  k  V  the volume of the c e l l .  i . e . moles hv/sec.  Ia = absorbed intensity i n  - 33 APPENDIX B - Watts e t . a l . Analysis Table IV t/°C  K/T  3.0  3.62x10  23.0  3.38x10  40.0  3.19x10  r/sec  rac -3 -3 -3  £n^-  ^sec T  .0000521  7.48x10  .000288  6.62x10  .000933  5.27x10  -7 -7 -7  T  69.7  4.24  435  6.07  1.77xl0  J  7.47  x is calculated using the equation: x(T) = [ k  l r  + k  l q  + k  2 q  e  AE  LF/kT]  1  taken from reference 9. k„ i s the rate constant of r a d i a t i v e decay for the lowest excited lr and k  n  state,  i s the rate constant for non-radiative decay from the same state.  iq k  2 q  i s the Arrhenius factor for non-radiative decay from a ligand f i e l d state  A E _ i n energy above the lowest excited state, T  k and T are the Boltzmann con-  stant and the temperature i n K respectively. P l o t t i n g £n — vs. — where A / T = k, we find E , = 15.0 kcal/mole and the x t 4 4 13 -1 Arrhenius factor A^ = 4.78 x 10 sec . The small discrepancy i n E ^ values i s due to a systematic error i n the T ' S calculated.  - 34 REFERENCES 1.  J.D. M i l l e r and R.H. P r i n c e , J . Chem. Soc. ( A ) , 1048 (1966).  2.  G.B. P o r t e r and H.L. S c h l M f e r , B e r . Bun. P h y s i c . Chem., 68, 316.  3.  G.A. Crosby, W.G. P e r k i n and D.M. K l a s s e n , J . Chem. Phys., 43, 1498.  4.  D.M. K l a s s e n and G.A. Crosby, J . Chem. Phys., 48, 1853 (1968).  5.  V. B a l z a n i , L. Moggi, M.F. M a n f r i n , F. B o l l e t t a and G.S. Lawrence, C o o r d i n a t i o n Chem. Rev., 15, 321 (1975).  6.  F. Zuloaga and M. Kasha, P h o t o c h e m i s t r y and P h o t o b i o l o g y , 7, 549 (1968).  7.  J.N. Demas and G.A. Crosby, J . o f M o l e c u l a s S p e c t r o s c o p y , 26, 72 (1968).  8.  J . Van Houten and R.J. W a t t s , J . Am. Chem. S o c , 98, 16, 4853 (1976).  9.  R . J . W a t t s , J.S. H a r r i n g t o n and J . Van Houten, Advances i n C h e m i s t r y S e r i e s , V o l . 168, P. 57 (1978).  10.  S. M a r k i e w i c z , M.S. Chan, R.H. S p a r k s , C.A. Evans and J.R. B o l t o n , I n t e r n a t i o n a l Conference on t h e P h o t o c h e m i c a l C o n v e r s i o n and S t o r a g e of S o l a r Energy, 24-28 August, Book o f A b s t r a c t s , P. E7 (1976).  11.  G. S p r i n t s c h n i k , H.W. S p r i n t s c h n i k , P.p. K i r s h and D.G. W h i t t e n , J . Am. Chem. S o c , 98, 8, 2337 (1977).  12.  C. C r e u t z and N. S u t i n , I n o r g . Chem. 15, 2, 499 (1976).  13.  J.N. Demas and J.W. A d d i n g t o n , J . Am. Chem. S o c , 98, 19, 5800 (1976).  14.  C . J . L i n and N. S u t i n , J . Phys. Chem., 80, 2, 97 (1976).  15.  P. N a t a r a j a n and J . F . E n d i c o t t , J . Am. Chem. S o c , 9416, 5909 (1972).  16.  K. Takuma, Y. Shuto and T. Matsuo, Chem. L e t t . P. 983 (1978).  17.  J.S. W i n t e r l e , D.S. K l i g e r and G.S. Hammond, J . Am. Chem. S o c , 98, 12, 3719 (1976).  18.  H.D. Gafney and A.W. Adamson, J . Am. Chem. S o c , 94, 23, 8238 (1972).  19.  J.N. Demas and A.W. Adamson, J . Am. Chem. S o c , 93, 7, 1800 (1971).  20.  M. G l e r i a , F. M i n t o , G. B e g g i a t o and P. B o r t o l u s , J . Chem. Soc. Chem. Comm., P. 285 (1978).  21.  P.E. Hoggard and G.B. P o r t e r , J . Am. Chem. S o c , 100, 5, 1457 (1978).  22.  F.H. B u r s t a l l , J . Chem. S o c , 34, P. 173 (1936).  23.  W.W.  B r a n d t , F.P. Dwyer and E.C. G y a r f a s , Chem. Rev. 54, 954 (1954).  - 35 24.  F.P. Dwyer and E.C. G y a r f a s , J . P r o c . Roy. S o c , New South Wales, 83 (1949).  25.  A. G a f n i and I.Z. S t e i n b e r g , I s r e a l J . o f Chem. 15, P. 102-105 (1977).  26.  P . J . G i o r d a n o , C R . Bock, M.S. W r i g h t o n , L.V. I n t e r r a n t e and R.F.K. W i l l i a m s , J . Am. Chem. S o c , 99, 9, 3187 (1977).  27.  M.S. W r i g h t o n and J . Morkham, J . Phys. Chem., 77, 26, 3042 (1973).  28.  P.P. Z a r n e g a r , C R . Bock and D.G. W h i t t e n , J . Am. Chem. S o c , 95, 13, 4357 (1973).  29.  Webster's 3 r d I n t e r n a t i o n a l D i c t i o n a r y o f t h e E n g l i s h Language, u n a b r i d g e d , M e r r i a n Co. S p r i n g f i e l d , M a s s a c h u s e t t s (1971)  30.  P r o g r e s s i n I n o r g a n i c C h e m i s t r y V o l . 17, I n o r g a n i c R e a c t i o n Mechanisms, I n t e r s c i e n c e P u b l i s h e r s , New Y o r k (1972), Ed. J.O. Edwards, P. 391, N. Serpone and D.G. B i c k l e y .  31.  G.A. Lawrence and D.R. S t r a n k s , I n o r g . Chem. 16, 4, 929 (1977).  32.  J . C B a i l a r , J r . , J . I n o r g . N u c l . Chem., 8, 165 (1958).  33.  P. Ray and N.K. D u t t , J . I n d i a n Chem. S o c , 20, 81 (1943).  34.  C S . S p r i n g e r , J r . , and R.C  35.  D.L. K e p e r t , I n o r g . Chem., 13, 1 1 , 2758 (1974).  36.  M.S. Henry, J . Am. Chem. S o c , 99, 18, 6138 (1977).  37.  F.M. Van Meter and H.M. Neumann, J . Am. Chem. S o c , 98, 6, 1388 (1976).  38.  N.A.P. Kane-Maguire and C.H. L a n g f o r d , J . Am. Chem. S o c , 94, 6, 2125 (1972).  39.  N.A.P. Kane-Maguire and C.H. L a n g f o r d , I n o r g . Chem., 15, 2, 464 (1976).  40.  M. Yamamoto and Y. Yamamoto, I n o r g . N u c l . Chem. L e t t . , 10, 1 1 , 691 (1976).  41.  N.A.P. Kane-Maguire, J.E. P h i f e r and C.G. Joney, I n o r g . Chem., 1 5 , 3, 593 (1976).  42.  B.E. B r y a n t and W.C. F e r n e l i u s , I n o r g . Syn., V o l . 5, P. 188.  43.  J.N. Demas and C M . F l y n n , J r . , A n a l y t i c a l C h e m i s t r y , V o l . 48, //2, P. 353, Feb. 1976.  44.  J . C C a l v e r t and J.N. P i t t s , J r . , P h o t o c h e m i s t r y , J . W i l e y and Sons, I n c , New Y o r k (1966), P. 783.  45.  A. J u r i s , M.T. G a n d o l f i , M.F. M a n f r i n and V. B a l z a n i , J . Am. Chem. Soc. 98, 4, 1047 (1976).  S i e v e r s , I n o r g . Chem., 6, 852 (1967).  - 36 -  46.  D. M e y e r s t e i n , J . R a b a n i , M.S. Matheson and D. M e i s e l , J . Phys. Chem., 82, 17, 1879 (1978).  47.  M. I r i e , T. Y o r o z u and K. H a y a s h i , J . Am. Chem. S o c , 100, 7, 2236 (1978).  48.  I . Jonas and B. Norden, I n o r g . N u c l . Chem. L e t t . , 12, 43 (1976).  49.  A . J . M c C a f f e r y , S.F. Mason and B.J. Norman, J . Chem. Soc. A, P. 1428 (1969).  50.  N.A.P. Kane-Maguire, R.M. T o l l i s o n and D.E. R i c h a r d s o n , I n o r g . Chem., 15, 2, 500 (1976).  51.  W.K. Chan, K. N a k a n i s k i , T.G. Ebrey and B. H o n i g , J . Am. Chem. S o c , 96, 11, 3642 (1974).  52.  Z. S e s t a k and S. Demeter, P h o t o s y n t h e t i c a 1 0 ( 2 ) :  53.  S.F. Mason, R.D. Peacock and T. P r o s p e r i , J . Chem. S o c , D a l t o n , P. 702 (1977).  182 (1976).  

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