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Energy transfer and complex formation in systems of aromatic hydrocarbons Moodie, Margaret Marion 1953

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ENERGY TRANSFER AMD COMPLEX FORMATION IN SYSTEMS OF AROMATIC HYDROCARBONS by MARGARET MARION MOODIE A THESIS SUMTTTED IN PARTIAL FUO'IIMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE .in the Department of Chemistry THE UNIVERSITY OF BRITISH COLUMBIA APRIL, 1953 We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF SCIENCE. 3SEEKSY TRANSFER AND COMPLEX FORMATION IN SYSTEMS OF AROMATIC.HYDRO CARBONS : The transfer of energy from one species of hydrocar-bon to another has been observed. The conditions under which such transfer occurs indicate that one aromatic hydrocarbon may be absorbed onto crystals of the other forming a surface complex with a binding energy of a few hundred calories. Transfer of energy occurs readily between the components of this complex but not between molecules of different hydrocarbons when both are i& solution. However, evidence for resonance transfer of energy between pairs of molecules of the same substance when both are in solid solution has been found. Studies of a large number of hydrocarbons have fai l e d to reveal any single electronic property of the molecule which determines i t s a b i l i t y to form complexes of the type found. The techniques developed were applied to a preliminary study of the rate of disappearance of carcinogenic hydrocarbons applied to the skin of mice. Also included are literature surveys on the known interactions of polycyclic hydrocarbons, the mode of reaction of carcinogenic hydrocarbons with l i v i n g c e l l s , and the spec-t r a l properties of chlorophyll. AOKNOMEDCiMENTS I want to express my sincere appreciation and thanks to my research supervisor, Dr. C. Reid, for his advice and assis-tance i n this research. I also wish to acknowledge my indebtedness to other sources: To the National Research Council of Canada for a hursary and a studentship To the National Cancer Institute of Canada, the National Research Council of Canada, and the President's Committee on Research of the University of Br i t i s h Columbia for grants with which equipment and supplies have been purchased. To Miss M. Nakashima and the Department of Anatomy, Univer-sity of Br i t i s h Columbia for assistance i n the care and painting of mice. To Dr. R. B. Kerr, Department of Medicine, University of Br i t i s h Columbia, who procured samples of human cancer tissue. To Professor E. Clar, University of Glasgow, for a sample of pentacene. To Dr. A. W. Johnson, University of Cambridge; for samples of coronene and perylene To Dr. R, N. Jones, National Research Council, Ottawa, for samples of acenaphthene9, 10-dibromo-anthracene, 9,10-di-(3-naphthyl anthracene, 9,10-diphenyl-anthraeene, 19-ethyl 1,2-benzanthracene, and 3 4,5,8,9,10-hexahydropyrene. To Dr. M. S. Newman, Ohio State University, for samples of 1,2-benzanthracene, i t s twelve mono-methyl deriv-atives, benzolc)phenanthrene, and i t s six mono-methyl derivatives. To Dr. R. B. Sandiin, University of Alberta, for a sample of 9,10-dimethyl anthracene. and To the Anatomy Department, University of Washington, for the use of a densitometer. TABLE OF CONTENTS FOR TEXT PAftF.  INTRODUCTION I.SHORT-RANGE FORCES -complexes 1.Examples of TT -complexes 1 2 .Theory of TT -complexes 2 B. Complexes of molecules containing atoms with un-shared electron p a i r s — 3 C. Complexes i n systems where quenching occurs 3 D. Complexes associated with spectral changes and photo-chemical reactions 4 E. Energy transfer involving short-range forces 5 II.LONG-RANGE FORCES A. ENergy transfer by means of electrons in conduction bands 6 B. Energy transfer involving long-range dipole-dipole forces 6 C. Possible overlap of transfer mechanisms 7 III. PROBLEM TO BE CONSIDERED A. Object of the experiments to be performed 7 B. Results of i n i t i a l work 9 ESTPERIMENTAL METHOD I. ARRANGEMENT OF APPARATUS 9 II. SOLVENTS • 10 III. SUSPENSIONS •• 10 IV. ABSORPTION STUDIES 13 V. PURITY OF MATERIAL 13 RESULTS I. SYSTEMS WITH TOO COMPONENTS IN SOLUTION A. Systems studied— 14 B. Efficiency of transfer process 17 C. Results with more concentrated solutions 17 II.SYSTEMS WITH ONE COMPONENT IN SOLUTION AND THE OTHER AS A SUSIENSION, THE LATTER ABSORBING RADIATION OF LOWER ENERGY THAN THE FOSMER 18 New emission bands 1. Systems of anthracene solution and naphthacene suspension ; 21 2. Systems of other hydrocarbons i n solution with naphthacene suspension 21 3. Systems of a hydrocarbon i n solution with anth-racene suspension 22 B. Solvent Effects 22 C. Fluorescence of energy donor 28 D. New absorption bands 29 E. Studies at -700C., at 20°C, and witn dry crystals- 29 III. SYSTEMS WITH ONE COMPONENT UsT SOLUTION AND THE OTHER AS A SUSPENSION, THE FORMER ABSORBING. RADIATION OF LOWER ENERGY THAN THE LATTER : 32 A. New amission and alifiorption bands • 32 B. Efficiency of the process 42 C. Effect of solvent and temperature 42 D. Dry crystals • 42 IV. SYSTEMS CONTAINING ONLY ONE AROMATIC HYDROCARBON COMPONENT A.' Systems containing anthracene— 46 B. One-component systems of other hydrocarbons 47 DISCUSSION I. SY TEMS WITH THO HYDROCARBONS IN SOLUTION 70 I I . INTERACTION MECHANISM FOR HYDRO C1AHBON'SOLUTION-SUSPENSION SYSTEMS — • 71 A. Influence of solvent '• 71 B. Possible "energy transfer" mechanisms 71 C. Evidence for a non-radiative process 72 D. Evidence for complex formation 77 HI.IMPORTANCE OF MICRO-CRYSTALS • 78 IV. ENERGY TRANSFER IN SOLUTION BETWEEN IDENTICAL MOLECULES A. Evidence for energy transfer between identical molecules 79 1, Systems with one hydrocarbon 2. Systems with two hydrocarbons B. Solvent effect 79 C. Significance of these observations 80 1. In solid systems 2. In l i q u i d solution V. MECHANISM OF TRANSFER FROM SUSPENSIONS OF ONE HYDROCARBON TO SOLUTIONS OF, ANQOEBER A. Transfer process i n suspensions • 82 B. Transfer process i n dry crystals 82 C. Reason for increased transfer efficiency 83 VI. CORRELATION OF COMPLEX FORMATION AND HYDROCARBON PROPERTIES , 83 A. Systems with transfer from molecules i n solution to micro-crystals 1. Systems with two different hydrocarbons 83 2. One-component systems- 85 B. Systems with transfer from micro-crystals to molecules i n solution 86 VII. GENERAL CONCLUSIONS 88 VIII. TRIPLET STATES 88 EC. PROPOSALS FOR CONTINUATION OF THE WORK - 89 APPLICATION OF RESULTS OBTAINED I. GENERAL APPLICATIONS 90 II. APPLICATION TO THE PROBLEM OF CARCINOGENESIS A. Experimental work: with human tumor tissue 91 B. Experimental work with mice 1. Methods of painting mice and extracting tissue 92 2. Results obtained 93 BIBLIOGRAPHY GENERAL REFERENCES ON AROMATIC HYDROCARBONS, COMPLEX FORMATION, AND ENERGY TRANSFER 97 REFERENCES ON ABSORPTION, EMISSION, COMPLEX FORMATION, AND PHOTO-CHEMICAL REACTIONS IN CHLOROPHYLL AND RELATED COMPOUNDS 106 REFERENCES ON ATTEMPTS TO ELUCISATE THE MODE OF REACTION OF CARCINOGENIC HYDRO CARBONS 109 APPENDICES APPENDIX 1- PURIFICATION OF MATERIALS USED I. Solvents used i n making glasses- 113 II . Aromatic hydrocarbons 113 APPENDIX 2-SYNTHESIS OF ANTHRACENE AND OF 2-METHYL ANTHRACENE I. Synthesis of anthracene A. Preparation of o-benzoyl benzoic acid 115 B. Preparation of anthraquinone : • 116 •C. Reduction of anthraquinone to anthracene- • — — 116 D. Other preparation methods • 117 II. Preparation of 2-methyl anthracene 117 APPENDIX 3- UNREPORTED TRIPLET LEVELS IN CERTAIN AROMATIC HYDRO CARBONS 118 APPENDIX 4-LITERATURE SURVEY ON MODE OF ACTION OF CARCIN-OGENIC HYDROCARBONS I. Activity of various compounds 120 II. Metabolism of compounds 120 A. Methods employed 120 B. Metabolic products and pathway 121 C. Effects on tissue 123 D. Studies of human cancer 123 III. Factors which influence the potency of carcinogenic hydrocarbons A. Solvent effects 124 B. Radiation effects 125 C. Mixtures of hydrocarbons 125 D. Addition of sulphur compounds 125 IV. Special reactions of hydrocarbons 125 V. Theories proposed to account for the carcinogenicity of certain aromatic hydrocarbons • 127 APPENDIX 5/LITERATURE SURVEY ON ABSORPTION AND EMISSION SPECTRA, PHOTO -CHEMICAL REACTIONS, COMPLEX FORMATION, AND ENERGY TRANSFER IN SYSTEMS CONTAINING CBLOROPHYLL I. Spectral properties of chlorophyll A. Cnloroplast pigments 130 B. Absorption, fluorescence, and phosphorescence bands— '• 130 C. Effect of solvent 130 D. Effect of temperature 131 E. Effect of state of aggregation 131 E. Photo-bleaching phenomena 132 II. Reactions of chlorophyll A. Chlorophyll as a sensitizer 132 B. Quenching i n systems containing chlorophyll 133 C. Chlorophyll complexes 135 III. Energy transfer phenomena in chlorophyll systems 136 IV. Possible photosynthesis mechanisms 137 TABLE OF CONTENTS FOR TABLES PAGE TABLE i . Occurrence and non-occurrence of energy trans-fer in systems which contain one component in solution and the other as a suspension 27 TABLE 2. Position, energy, and shift of the center of the highest energy emission band of the component in solution in systems where there i s energy transfer from the component i n suspension 41 TATW- 5. Absorption and emission band maxima for transfer systems containing naphthacene solution 43 TABLE_4. Properties of the emission of suspensions of a single aromatic hydrocarbon •— 50 TABLE 5. The shift of the naphthacene solution band com-pared with the carcinogenic activity of the suspension component 87 TABLE 6. Unreported t r i p l e t emissions and the emission bands of the respective trinitro-benzene complexes 119 TABLE OF CONTENTS FOR FIGURES PAGE FIGURE 1 - Diagram of apparatus-— 11 FIGURE 3 - Photograph of apparatus 12 FIGURE 5 - Emission of anthracene-naphthacene system r — 16 FIGURE 4 - Emission of a terphenyl-diphenylhexatrine solution system 19 FIGURE 5 - Emission from systems of naphthacene suspension and a solution of a second hydrocarbon which absorbs higher energy radiation 24 FIGURE 6 - Emission from systems of anthracene suspension and a solution of a second hydrocarbon which absorbs higher energy radiation — 26 FIGURE 7 - Absorption of anthracene solution-naphthacene suspension system 30 FIGURE 8 - Emission from systems containing naphthacene solution and a suspension of a second ^hydrocarbon which absorbs at higher energies— 34 FIGURE 9 - Emission from systems containing a solution of anthracene, 2-methyl anthracene, or phenanth-rene and a suspension of a second hydrocarbon which absorbed only at higher energies 36 FIGURE 10- Emission from systems containing a solution of a 1,2-benzanthracene derivative and a suspens-ion of naphthalene or terphenyl 38 FIGURE LL- Emission from systems containing a solution of benzo(c)phenanthrene, one of i t s methyl deriv-atives, diphenylhexatriene, or trans-stilbene and a suspension of naphthalene or terphenyl— 40 FIGURE 12- New absdption bands of an anthracene suspension-naphthacene solution system 44 FIGURE 13- Self transfer i n anthracene 48 FIGURE 14- Self transfer in chrysene 51 FIGURE 15- Emission from one-component hydrocarbon systems- 53 FIGURE 16- " n tt « rt u 5 5 FIGURE 17- " « • II tt tt tt 5 7 FIGURE 18- " " " " " rt — 59 PAGE FIGURE 19 - Emission from one-component hydrocarbon systems- 61 FIGURE 20 - " » " " " « 63 FIGURE 21 - " " " " " - 65 FIGURE 22 - « M t. it « " - 67 FIGURE 25 - " " « " '» " - 69 FIGURE 24 - P o t e n t i a l energy curves f o r ground and excited states of a molecule 73 FIGURE 25 - Ef f e c t of the state of aggregation of the receiving substance on transfer ' 74 FIGURE 26 - Transmission measurements of naphthacene 75 FIGURE 27 - Rate of disappearance of hydrocarbon painted on the skin of mice 94 ENERGY TRANSFER AND COMPLEX FORMATION HT SYSTEMS OF  AROMATIC HYDROCARBONS. INTRODUCTION Various observers nave reported the occurrence of processes which involve the apparent inter - and intra-molecular migration of energy and which must play an important role in many biological and chemical phenomena. 19,33,57,59-61,81,180 The transferred energy may be dissipated as heat by the appector molecule, re-emitted as li g h t , or used to promote a chemical reaction. Most of the work in this f i e l d has been concerned with the second of these processes which may be detected by observing the flourescence of the acceptor molecule. The Black* ening of a s i l v e r halide grain by a process involving primary energy absorption by a sensitizer dye typifies the third mech-anism. I. SHORT -RANGE FORCES  A.TT - complexes 1. Examples of TT-Complexes Interactions between molecules may involve either short-range or long-range forces. Much of the knowledge sbout short-range ( i . e . 1 to 10 A.) forces has resulted from studies of'fT- complexes. These may be defined as compounds containing a covalent or co-ordin-ate link i n which the donor mofcecule or atom carries TT - elect-/"* 41 42 rons rather than unshared *° electrons. ' Although many of these TT - complexes exist only i n minute concentrations as 42 l Q S transient intermediates in certain organic reactions, ' there are some complexes of sufficient s t a b i l i t y to allow a study of their properties to be made. For example, the appearance of a new ultra-violet absorption band and the variation of i t s intensity with changes in concentration permit the calculation of equilibrium constants for the complexes which form between iodine, bromine, chlorine, iodide chloride, sulphur d i o x i d e , 6 ' 7 ' 1 3 ' 1 4 , 8 4 ' 8 5 ' 1 0 2 oxalyl c h l o r i d e , 1 5 8 or silver i o n 5 ' 1 0 3 and aromatic hydrocarbons such o as benzene, toluene, xylene, etc. At 77 K. there i s similar evid-ence for a 1:1 addition compound between iodine and olefins such 62 as propene or 1,3-butadiene. The best known "TT -complexes are the brightly coloured crystalline picrates anqUtrinitro-benzene derivatives of arom-ati c hydrocarbons and h e t e r o c y c l i c s . 1 3 9 ' 1 5 2 ' 1 8 9 QtherTT-complexes also form between aniline and nitro aromatic hydrocarbons 1 1 1, 125 between heterocyclics and nitro-phenols , and between nitro-45 naphthol and li q u i d ammonia. Aromatic hydrocarbons also form • 39 molecular compounds with sterols i n mixed surface films, with p urines, 1 8 6 and with hydrogen f l o u r i d e . 1 0 5 S t i l l other examples of 1T -complexes are the-^efatradiol-sulphuric acid complex, 1 1 6 the complexes of nucleic acid with a c r i f l a v i n e , 1 4 0 141 auramine-0 or streptomycin and the complex of riboflavin 163 with the enzyme lysozyme. Complex formation i s probably of 173 fundamental importance in photosynthesis and in the action of carcinogenic compounds. 4,28 2. Theory of ff -complexes. A theoretical formulation of the structure of these - 3 -"fT" J 1 R Q A~\ AO ii - complexes has been built up by i'leiss, Dewar, ' 29 1"^ 5 Braekmann, and Mulliken. ° The mechanism involved i s an essentially "Lewis acid-base" interaction involving a quantum mechanical reasonance between a "no-bond" structure an d a struc-ture with a bond between the two atoms or molecules. Strong absorption bands belonging to the complex as a whole are pre-dicted. The theory also makes a distinction between dispersion forces and charge-transfer forces. More recently Shuler ^ 9 proposed a free-electron model for TT -molecular complexes whicn predicts results agreeing with experiment and with Mulliken^s L.C.A.O.-type theory. For the simple complexes of the benzene-iodine type, the wave-lengths of the charge transfer spectra show an excellent correlation with the ionization potentials of the electron donor, and the intensities of the transitions are markedly 123 dependent on the electron acceptor component. B. Complexes of molecules containing atoms with unshared electron pairs There are complexes in which an unshared pair of electrons act in a manner similar to the Tf -electrons i n the complexes already described. New absorption bands and equilibrium constants have been found for iodine-n-butyl alcohol or other complexes. Conductance measurements have verified the existence of complexes between aluminum bromide and acetic anhydride, 174-177 acetone, ammonia, dimethyl ether, methanol, or trimethylamine. C. Complexes in systems where quenching occurs Often there i s quenching or a marked decrease i n the - 4 -flourescence yield of a substance on increasing i t s concentrat-124 ion or on adding a small amount of a second, substance. For example, the flourescence of many anthraquinones i s quenched by Qfi oxygen; ° that of many aromatic hydrocarbons by oxygen, sulphur dioxide, carbon tetrachloride, p-bromo-aniline, 1 7' 1 8' 2 1' 2 3' 2 6' 101,131,188 ethyl i o d i d e , 1 0 0 or caffeine i o n ; 1 8 7 and that of 3-70 amino phthallmide or sodium salicylate by organic dyes. As the quenching process i s entirely reversible, no true chemical action must take place. Theories involving deactivating eollise 69 io$s or classical electrodynamic forces have been propesed. o However, complex formation involving van der Waal's forces ( i . e . dipole attractions and dispersion forces) seems to provide the most readily accepted explanation, especially i n systems where 157 181 183 184 quenching shows a negative temperature coefficient. , The failure to find new absorption bands i n some of the quenched systems may be explained on the suggestion that the complex i s formed between an excited molecule and a quenching molecule, 4 7 or on the possibility that the bands l i e in spectral regions which have not been examoned. Evans has just reported that many compounds combine with oxygen to give complexes 49 which absorb i n the region near 2300 A. D. Complexes associated with spectral changes and photo-" ' chemical reactions Short-range forces, involving the possible formation of loose molecular complexes, are probably important i n systems of aromatic hydrocarbons or certain dyes where a change of solvent shifts the solution absorption h a n d s . 9 ' 1 1 ' 3 6 ' 1 0 4 ' 1 1 2 > 1 2 2 » 1 6 1 - 5 -Molecular complexes are possible intermediates in certain photo-50,51 inactiviation, pao oxidation e f f e c t s . 2 0 ' 2 7 ,51 44 l f i n 1Q4. inactiviation, ' paotosensititization, , X D U ' " L y o , - L y * or photo-E, Energy transfer involving short-range forces The energy transfer mechanism 5 7 , 6 0 which w i l l be considered f i r s t must involve short-range forces as i t occurs only i n systems where there i s a possible overlap of the orbitals of adjacent molecules. The energy exchange may occur between a pair of molecules, or i t may involve a succession of such exchanges. The occurrence of the latter process in a periodic system i s often referred to as "exciton movement". This term, •,has however, been used rather loosely to describe phenomena of various kinds since i t s introduction by Frenkel. ' Phenomena which have been attributed to a transfer mechanism of this kind are found i n (1) Polymers of pseudo-cyanines 8 6> 8 9> 9 0> 1 2 6> l e 4> 1 9 3 (2) Inorganic phosphors in which no free electrons 1 5 or holes seem to be produced (3) Crystals of aromatic hydrocarbons such as naph-thalene and anthracene containing traces of anthracene or naphthacene impurity respect-a b l e , 22, 24, 25, 71, 110, 117, 118,130,^ (4) Solutions of flourescent hydrocarbons in plastics such as p o l y s t y r e n e 3 4 ' 1 0 8 ) 1 6 2 and in liquids such as xylene 66,92-94,109,154,155, which show successive short-range transfers under X-ray irradiation. This group has been studied - 6 -extensively as possible s c i n t i l l a t i o n counters. II. LOHG-RANGE FORCES In systems where short-range forces are precluded, weaker long-range forces may play a part. The other two methods of energy transfer which have been, studied imvolve predominantly long-range" ( i . e . 10 to 200 A.) forces. 38.40.57,60,88,129 A. Energy transfer by means of electrons i n conduction bands. One method of long-range energy transfer i s by means of electrons which are excited into a conduction band and which are subsequently trapped, usually by an impurity m o l e c u l e . 4 6 ' 4 8 ' 5 8 , 72 91 ' ' Most solid inorganic phosphors provide examples of this mechanism. B. Energy transfer involving long-range dipole-dipole forces The third transfer process, which involves long-range dipole-dipole interaction, was f i r s t observed in vapour-phase mixtures of mercury and thallium, aniline and indogo, and ben-zene and aniline i n each/pair of which the fluorescence of the f i r s t substance i s quenched and that of the second i s increased. 33,55,57,60,95, gg c e j l t i y , energy transfer from naphthalene vapour to acridine vapour was reported.1'''2 Quantitative investigations have shown that, in the gas phase and probably also in solution, such transfers occur at distances much greater than the usual 143 c o l l i s i o n diameter. Eorster has suggested that transfer bet-ween trypaflavin and rhodamine-B i n solution may occur over - 7 -distances of the order of 60 A. and that this i s in good agree-ment with the calculated distance assuming that only dipole-54-57 dipole interactions are involved. Galanin also reports a 6 8 similar transfer of energy from anthracene to acridine orange. C. Possible overlap of transfer mechanisms Some examples of observed energy transfer cannot definitely be assigned to one of these three classes, while i n other cases a combination of mechanisms i s responsible for the phenomenon. Whether there i s a real distinction between the f i r s t two transfer processes mentioned i s now uncertain. The second process i s always accompanied by photo-conductivity; and although i t i s not usually considered that the kinds of molecule taking part in the f i r s t process are photo-conducting, recent work, especially with anthracene and certain dyes suggests that they may be. 2» 1 2» 1 36,178,179 Measurements of ultrasonic absorption and velocity i n ois andjtrains dichloroethylene vapours indicate that short-range, but not long-range, forces are able to change the transition probability between translational and vibrational energy states. III. PROBLEM TO BE CONSIDERED A. Object of the experiments to be performed In view of the calculations and experiments of Forster 5 4 ~ 5 7 a n d Galanin 6 8 which suggest that long-range energy transfer processes should occur in solution, the behaviour under irradiation of pairs of aromatic hydrocarbons i n solution i s of interest. - 8 -In the discussion of short-range forces i t is noted that energy-transfer can occur i f the solvent itself is an absorber as in the case of (1) the hydrocarbon solutions irradiated with X-rays 34,66,92-94,108,109,154,155,162 and (2) the hydrocarbon crystals containing a small amount of a second hydrocarbon and irradiated ^ t . ultra-violet l i ^ t . " . ^ ^ ; ^ . ^ . ^ . The experiments to be described are designed to in-vestigate systems in which the solvent has energy levels too high for i t to be excited by the radiation used. It is clear at the outset that in such solutions transfer of energy does not occur with an efficiency at a l l comparable to that of the process occurring in crystals. Thus anthracene crystals, con-taminated with sufficient naphthacene (1 part in 10 ) to show strongly the characteristic naphthacene green emission, 1 5' 1 1 7' 1 1 8 fluoresce only in the bljte when dissolved and show no trace of naphthacene emission even after quite long exposure times. In order to examine this qualitative observation more carefully, use has been made of solutions of pairs of hydrocarbons in inert solvents which form glassy solids at - 180°C. Under these conditions collision quenching is elim-inated and fluorescence yields are high. Transfer of electronic energy during collisions is also prevented, and thus i t is possible to estimate the average distance between molecules of the two components assuming a random distribution. - 9 -B. Results of i n i t i a l work « 132 133 The i n i t i a l work on this subject ' showed that under these conditions, no evidence for long-range inter-molee-ular transfer of energy between molecules of anthracene and o naphthacene i n an alcohol-ether-isopentane solvent at -180 C. can be found. In heterogeneous systems where the naphthacene i s present i n micro-crystalline form and the anthracene i s dissolved i n the glassy matrix, highly efficient transfer of energy from the dissolved to the solid component i s observed. The extension of this work to other two-component hydrocarbon systems i n a variety of solvents, and to one-component systems w i l l now be 134 described. EXIERBffiNTAL METHOD. I..ARRANGEMBKT Oi1 APPARATUS The aromatic hydrocarbons were dissolved or suspended in solvents of varying polarity which formed clear glasses when cooled i n liq u i d nitrogen contained in an unsilvered Dev/ar vessel. The resulting systems were irradiated with monochromatic light 98 from a General E l e c t r i c AH 6 mercury arc with auitable f i l t e r s . The fluorescence from the solution and any scattered mercury light were photographed using an E2 Hilger quartz prism spect-rograph. The resulting plates were scanned with a Kipp and Zonen densitometer equipped with a paper recorder. During the f i n a l year of work the use of plates was eliminated, and traces were obtained directly by use of the Hilger Scanning Unit and Recorder which was attached directly to the spectrograph (figures - 10 -1 and 2) . Many of the hydrocarbons showed a long-lived phos-phorescence with a half-life of one to ten seconds in addition -8 43 97 99 to the usual fluorescence with a 10 second half-life. 114,115,120,121,151 TO obtain a phosphorescence spectrum comple-tely free from fluorescence and scattered mercury light, the Dewer flask in the arrangement described previously was placed inside an empty can with a hole cut in one side; and the can was rotated so that the hole faced the incident mercury arc beam at one instant, and allowed any long-lived emission to enter the spectrograph s l i t a short time later. II. SOLVENTS The solvents used, in order of decreasing polarity, were (1) eight parts of methanol, one of ethanol, and one of iso-propanol; (2). EPA or five parts of ethery five of isopentane, 115 and two of ethanol; (3) one part of ether to five of iso-pentane; (4) one part each of ether and methyl cyclohexane to four of isopentane; (5) one part of isopentane and four of methyl cyclohexane; and (6) one part of methyl cyclohexane to four of isopentane. III. SUSPENSIONS Suspensions were made by rapid cooling of supersatur-ated solutions or, when high concentrations were required, by mechanical dispersion. As reproducibility in particle size and density was difficult to attain, small variations from experiment to experiment were inevitable. - 11 -FIGURE 1-DIAGRAM OF APPARATUS« Transformer for AHG mercury arc Scanning Unit containing-•Photo-multiplier 2 . S l i t adjustment 3.MoJ;or drive & sele c t i o n of traversing speed 4»Wave-length marker 5•Fatiguing lamp Recorder Unit containing 1. H.T.battery c i r c u i t 2. Photo-multiplier c i r c u i t 3 . Galvanometer c i r c u i t 4 . S e n s i t i v i t y control 5 . Wave-length marker c i r c u i t 6. Drum camera with casette holding photographic paper - 1 2 -FIGURE S- Photograph of apparatus " ^ Fan to prevent the condensation of moisture on the dewar •^Box containing AH* arc & f i l t e r s •--jJDewar containing sample i n l i q u i d nitrogen vHilger E 2 spectro-graph •^Scanner and attached photocell -^Transformer for AH* arc r - ^ B a l l i s t i c galvano-meter ..^  Light to shine on mirror attached to galvanometer •>Case containing batteries and amplifier •^Casette containing photographic paper on which trace i s recorded For studies at -70 C. the coolant was a mixture of ether and isopentane cooled with l i q u i d mitrogen. (Dry ice baths gave cloudy, fluorescent coolants unsuitable for our purposes.) Suspensions at - 70°C. and at 20°C. were stirred continuously during the exposure time to prevent settling out. IV. ABSORPTION STUDIES Because of the d i f f i c u l t y i n obtaining low temperature measurements with a standard Beckmann Spectrophotometer, the rather qualitative absorption studies were made by passing a light beam from a tungsten filament lamp through the sample and into the spectrograph. V. PURITT OF MATERIAL As in a l l fluorescence work, high purity of both solvents and solutes was essential since impurities might act as acceptors of energy absorbed by the major components. The solvents were r e d i s t i l l e d frequently 8 > 1 4 6 and sometimes chromatographed. 1 9 6 The hydrocarbons were f i n a l l y purified by chromatographing through an alumina column with a benzene-petroleum ether mixture as solvent. Complete details of the purification process are given i n Appendix 1. It w i l l be shown later that i t i s almost impossible to obtain hydrocarbons completely free of minute traces of other hydrocarbons. - 14 -RESULTS I. SYSTEMS WITH TW COMPONENTS IN SOLUTION  A. Systems studied In any of the six solvents already l i s t e d and at temperatures of both - 180°C, and 20°C. there i s no observable interaction between the molecules of two different aromatic hydrocarbons when both substances are i n true solution. Thus in Figure 3 (a),w(b), and (c) the fluorescence of a system con-taining both anthracene and naphthcene i s just the sum of that of the individual components. To arrive at this conclusion several hundred exposures under different conditions of solvent polarity, temperature, and hydrocarbon concentration were made with the following pairs of hydrocarnons: naphthacene with acenaphthene, anthracene, 9,10-dibromo-anthracene, 9,10-di-chloro-anthracene, 9,10-dimethyl anthracene, 9,10-diphenyl anthracene, 2-methyl anthracene, 1,2-benzanth-racene and i t s twftlve mono-methyl derivatives, 9,10-dimethyl-l,2-benzanthracene, benzo(c)phenanthrene, and i t s six mono-methyl derivatives, benzene, chrysene, coronene, 1,2,5,6-dibenzanthracene, diphenylhexatriene, fluoranthene, fluorene, 3,3,4,8,9,10-hexahydrowpyrene, naphthalene, - 15 -FIGURE 5- Emission of anthracene-naphthacene system irrad-iated with Hg 3650 A. The solvent used i n a l l cases i s EPA. (In a l l emission spectra traces the ordinate D represents optical density, while the abscissa gives the wave-length in milli-microns} Dashed curves show anthracene emission; solid and clotted curves show naphthacene emission. F i r s t column, naphthacene in solution (a) naphthacene alone at -180°C. (b) same naphthacene concentration as (a) with added anthracene, also in solution at -180°C. (c) as (b) at 20°C. Second column, naphthacene i n suspension (d) naphthacene alone at -180°C. (e) same naphthacene concentration as (d) with added anthracene in solution, also at 9 180° C. Upper dotted curve shows the effect of a three-fold increase in anthracene concentration, the naphthacene concentration remaining unchanged. (f.) naphthacene suspension containing anthracene i n solution at 20°C. Third column, anthracene in suspension (g) anthracene alone at -180°C (h) same anthracene concentration as (g) with naph-thacene in solution to give a naphthacene-anthracene ratio of 1: 10 5 at - 180°C. (i) anthracene suspension and naphthacene in solution at 20°C. 2-naphthol, pentacene, perylene, phenanthrene, terphenyl, toluene, or trans-stilbene anthracene with acenaphthene, benzene, fluorene, 3,4,5,8,9,10 hexahydropyrene, naphthalene, 2-naphthol, pentacene, terphenyl, or toluene naphthalene or terphenyl with 1,2, benzanthracene and i t s twelve mono-methyl derivatives, 9,10 dimethyl-1,2,-benzanthracene, benzo(c)phenanthrene and i t s six mono-methyl derivatives, chrysene, 1,2,5,6 -dibenzanthracene, diphenyl-hexatriene, or fluoranthene B. Efficiency of transfer process It i s estimated that a systematic ten to twenty percent increase in intensity would have been detected, and in systems consisting of a tenfold excess of "donor" over "recei-ver" molecules this could be achieved with a transfer e f f i c -iency of only one to two percent. Concentration ratios of donor to receiver as high as 1000:1 s t i l l showed no detectable effect, so that "less than five percent" i s a very concervative estimate of the efficiency of the transfer process in solution under the conditions of our experiments. C. Results with more concentrated solutions It was f e l t that these negative results might arise - 18 -from the limitation of concentration imposed by the rather low solu b i l i t y of the aromatic hydrocarbons in the solvents used. Of the six solvents l i s t e d previously, EPA dissolves the'largest quantities of hydrocarbons; but i n i t the approximate -4 concentrations attainable at -180°C are only 3.56 x 10 moles per l i t e r for anthracene, 1,18 x IO" 4 moles per l i t e r for -5 chrysene, and 1.54 x 10 moles per l i t e r for naphthacene. (These are the highest concentrations at which no separation of solid was visible on cooling to -180°C. with cross illumination. Usually the appearance of visible turbidity and the observation of a characteristic emission of the "solid" could be correlated.) A xylene solution containing terphenyl and diphenyl--2 hexatriene at concentrations of 1.30 x 10 moles per l i t e r and 4.31 x 10~5 moles per l i t e r respectively, on irradiation at 20° C. with, either Hg 2536 A. or Hg 3130 A. showed that the fluor-escence of the combined system was equivalent to the sum of that from the systems containing only one dissolved component (Figure 4). Kallmann and Furst fi6,94 have reported, however, that on irrad-iation with X-rays the system containing both terphenyl and diphenylhexatriene shows only a fluorescene which i s char-acteristic of diphenylhexatriene and which i s of greater inten-sity than that from a system containing only diphenylhexatriene. II. SgSTEMS WITH ONE COMPONENT UJ SOLUTION AND THE OTHER AS  A SUSPENSION, THE LATTER ABSORBING- RADIATION OF L01EER ENERGY THAN THE FORMER - 19 -FIGURE 4- Emission of a terphenyl-diphenylhexatriene solution system i n xylene at 20°C. and irradiated with Hg 3130 A. Broken curve shows terphenyl emission and the solid curve diphenylhexatriene emission. -2 (a) Terphenyl solution of 1.30 x 10 moles per l i t e r and -5 diphenylhexatriene solution of 4.31 x 10 moles per l i t e r i n separate systems (b) Terphenyl and diphenylhexatriene at the above concentrations in the same system - 21 -There i s definite evidence of energy transfer in systems containing a micro-crystalline suspension of one of the hydrocarbons. This section i s concerned only with systems where .the micro-crystalline component absorbs radiation of a lower energy than that absorbed by the component in solution, A. Hew emission bands 1. Systems of anthracene solution and naphthacene suspension At -180°C. the addition of an anthracene solution to a suspension of naphthacene produces a new rather broad and intense emission band at 5530 A. (Figure 3 (d) and (e) ) whose intensity i s proportional to the anthracene concentration. Irradiation of this system with each of Hg 3125 A., Hg 3650 A., Hg 3125 and 3650 A., and Hg 4040 and 4358 A. effects no change i n the relative intensities of the bands beyond 4700 A. even ' ..though the Hg 4040 and 4358 A. radiation i s not ab-sorbed by the anthracene in solution, Increasing amounts of suspended naphthacene give the expected increase in the fluor-escence intensity of both the naphthacene system and the anth-racene-naphthacene system. However, a comparison of the fluorS escence intensity of the naphthacene suspension system with the intensity of the 5330 A. band obtained on adding anthracene solution shows that, for a given anthracene concentration, the resulting increase in intensity i s greater for the more dilute naphthacene suspensions. 2. Systems of other hydrocarbons i n solution with naphthacene suspension The results of studies made with systems containing \ - 22 -other hydrocarbon pairs are presented i n Figures 5 and 6 and i n Table 1. It w i l l be seen that i n the chrysene solution-naphtha-cene suspension system the band centre i s shifted to 5440 A.; while with 1,2,5,6-dibenzanthracene solution the band occurs at 5500 A. Special, mention should be made of the phenanthrene sol-ution- naphthacene suspension system (Figure 5 (e) and (f) ) where i t w i l l be observed that the new emission band occurs in the region of the phenanthrene t r i p l e t emission. (Further discussion of the t r i p l e t emission w i l l be flound i n Appendix 3.) Although the total intensity increase i s not as great as in the other systems, the new emission band i s distinct from any of the phenanthrene bands. 3. Systems of a hydrocarbon in solution with anthra- cene suspension In systems containing anthracene suspension, the addition of solutions of naphthalehe, 2-naphthol, or terphenyl effects an intensity increase i n the 4140 A. band which i s char-acteristic of anthracene suspension in non-polar solvents (figure 6 (a) to (d) However, i n polar solvents the 4140 A. band i s distinct from the emission of the anthracene suspension alone (Figure 6 (e) and (f) ). In Part IV of the Results w i l l be found a f u l l discussion of the solvent effect on anthracene suspension emission. B. Solvent Effects The occurrence or non-occurrence of this new emission band depends on the polarity of the solvent, In systems with anthracene in solution and naphthacene suspension the band I - 23 -FIGURE 5. - Emission from systems of naphthacene suspension 1 1 b and a solution of a second hydrocarbon, which absorbs higher energy radiation, in methyl cyelohexane-isopen-tane solvent at 180°C. A l l traces have the same expos-ure time. Solid curves show naphthacene emission, while broken curves show emission of the hydrocarbon in solution. • (a) naphthacene suspension alone (b) same naphthacene concentration as (a) with added 2-methyl anthracene i n solution (c) same naphthacene concentration as (a) with added chrysene in solution (d) same naphthacene concentration as (a) with added 1,2,5,6-dibenzanthracene i n solution (e) same naphthacene concentration as (a) with added phenanthrene in solution (f) phenanthrene solution alone at the same concen-tration as (e) (g) same naphthacene concentration as (a) with added 1,2-benzanthracene in solution (h) same naphthacene concentration as (a) with 10-methyl-l,2,-benzanthracene in solution . - 24 -5 (a) (b) 1* / 1 • A \ \ • / \ i i i i 1 i i ""i ,\ 1 i i i 111 111 / N ^ i f o o ' • •so 5 O 0 S S O < " 0 O (c) i :. \ I I I \ to.i* \ i i i V 1 i i -*—rY^ii i 111.i 1111 V i f O O 4 5 0 s o o s s o too (d). A \ 1 • o 1 1' ' > I \ 1 ' 1 1 o \ | i i I i 1 V I>T t-^PTi I i I i i t Ii I V *i»oe t-so soo sso boo (6) 4 <l » * ' ' A * /• ! '•" ' 1 Y ' / 4 ' 4 I \ 1 • x i \ 1 i i i 1 i i i i 1 i i i i Ii i i i 11/"*— WOO * 5 0 i * SOO ^ 5 O ( e O O " » Cf) 1 11 l ' > i ' i ! i » , i , 1 '• i': :i? .". ', i i ; • • ' • i i ' • i ' 4 J , 1 i V P I V / • 1 \ I V V I I I I I 1 I i I 1 1 1 1 1 1 1 I I lU. IfOO i t s o 9oo 5So too ' i ' »' ' / \ _i i i i 1 i . I T 4 M i 111111K*!^. Woo w s o s o o sso faoo /. (h) i !. 1 ' 1 • 1 >. 1 1 ' • , ' • • ' , 1 A i i i i 1 i 4 - r * 7 r i i i 111111 KlSv SOO sso t o o !*oo U.SO 5oo s s o too A (nrya) FIGURE 5. - 25 -FIGURE 6- Emission from systems of anthracene suspension and a solution of a second hydrocarbon, which absorbs higher energy r a d i a t i o n at -180°C. Traces (a) to (d) are i n methyl cyclohexane-isopentane solvent and have the same exposure times. Traces (e) and (f) are i n EPA and have the exposure times. (a) anthracene suspension alone (b) same anthracene concentration as (a) with added naphthalene i n solution (c) same anthracene concentration as (a) with added 2-naphthol i n solution (d) same anthracene concentration as (a) with added terphenyl i n solution (e) anthracene suspension alone (f) same anthracene concentration as (e) with added 2-naphthol i n solution - 27 «-TABLE 1. Occurrence and non-occurrence of "energy transfer" at -180°C. in systems which contain one component in solution and the other as a suspension. The latter absorbs radiation of lower energy than the former. COMPONENT IN SUSPENSION COMPONENT IN SOLUTION OBSERVED "ENERGY TRANSFER" rfAVE-LENGTH of New EMISSION BAND j SOLVENTS IN WHICH COMPLEXES FORM. Naphthacene lAcenaphthene " ]Anthracene " |2-mjethyl anthracene 1 no yes yes 5330 A 5320 A. • Isopentane-methyl cyclohexane, 1 ether-isopentane, EPA t ' , . | Isopentane-methyl cyclohexane, | ether-isopentane, EPA 1 II II II II II It tt It tt 11 II II It t i II If II 11 t l tl tt II 11 It II t i H it it n t l ti t l t i ti II i l it It anthaacene 2-methyl anthracene 9,10-dibromo-anthracene 9,30-di- <& -naphthyl- " 9,10-di-phenyl- " 1,2-benzanthracene t i i i ti t i i i tt n n t i n tt tt t i it t i it ti t i it it i i I! II II It It t l II II t l II II II II II i9,10-dibromo-anthracene 19,10-di-^-naphthyl-anthracene 19,10-dichloro-anthracene \9,10-diphenyl anthracene \9,lO-demethyl-anthracene |1,2-benzanthracene fl * methyl 1,2-benzanthracene 121 " II « 13 SS 6 •1 ?8 9 ID CIO ethylv i i it it it it it it t i it tt t i i i it it tt ti it tt it t i n tt it t i it ti n it i i II it it tt 9,10 dimethyl 1,2-benzanthracene JBenzene jbenzo(c)phenanthrene >1 methyl benzo(c)phenanthrene 12 « ?3 II it U " " )5 " 6 " " it it ti it ti ;20-methyl cholanthrene ;chrysene jcoronene i1,2,5,6-dibenzanthracene idiphenylhexatriene Jfluoranthene jfluorene •3,4,5,8,9,10-hexahydropyrene /naphthalene |2-naphthol jperylene \phenanthrene pyrene . iterphenyl tetralin Itrans-stilbene lacenaphthene Jfluorene j 3,4,5,8,9,10-hexahydropyrene ;naphthalene j2-naphthol \ teiphenyl )naphthalene1 I " : ; it 1» methyl 1,2-benzanthracene 2«. 3' 4» 3 4 50 6 7 8 9 10 10 ethyl 9,10-dimethyl 1,2-benzanthracene it tt it it it tt it t i t i i i n ti t i it Chrysene Coronene 1,2,5,6-dibenzanthracene it ti diphenylhexatriene tt n it n ti |2-naphthol jnaphthalene \anthracene vfluorene !- 2-naphthol I anthracene f fluorene I naphthalene 'I 2-naphthol 'l terphenyl I trans-stilbene no no no no mo no no no no no no no no no no no no no no no no no no no no no no no no yes no yes no no no no no no no yes no no no no no no no yes yes yes no no no no no no no no no no No no no NO no no no no no no no no no no no no no no no no ! 5440 A. j 55PO A. 5380 A, 4140 A. it | Isopentame-methyl cyclohexane, | ether-isopentane I I Isopentane-methyl cyclohexane, I ether-isopentane | Isopentane-methyl cyclohexane, f ether-isopentane, EPA, )EPA, ether-isopentane, )isopentane-methyl cyclohexane ) fluoranthene II phenanthrene I naphthalene ! terphenyl |. naphthalene no no no - 28 -appears with the same intensity in both EPA and methyl cyclo-hexane-isopentane solvents. However, din the more polar alcohol glass the fluorescence i s just the sum of that from the separate components. Similarly, only i n the less polar methyl cyclohex-ane-isopentane glasses i s there any appreciable interaction in systems containing chrysene or 1,2,5,6-dibenzanthracene in sol-ution and naphthacene suspension. That these effects are not simply due to solubility changes was established by using an amount of the crystalline hydrocarbon well in excess of i t s solubility in any of the solvents and a constant amount of the dissolved hydrocarbon i n each case. No energy transfer could be detected in any of the glassy solvents used for many systems such as those containing naphthacene suspension and solutions of 9,10-dibromo-anthracene, 1,2-benzanthracene (Figure 5 (g) ), or pyrene. That this i s not due to a lower solubility of these hydrocarbons i s shown as follows. If to 7.0 mis. of ether-isopentane solvent containing 1 mg. of naphthacene suspension is added 0.02 mg. of anthracene, the new emission band definitely appears at -180°C. If 0.15 mg. of either 1,2-benzanthracene or 10-methyl-l,2,-benzanth-racene i s added, there i s no change in the typical naphthacene emission (Figure 5 (g) and (h) ). C. Fluorescence of energy donor Although no, really quantitative measurements were made, i t was noted that whenever energy transfer occurred there was usually a significent decrease in the fluorescence intensity of the component in solution and that very l i t t ^ e p f i f - 29 -any, intensity decrease occurred when there was no energy transfer. No quantitative determination of the minimum amount of anthracene needed to make the 5330 A. band visible was poss-ible, for when the new emission band becomes weaker, i t is obscured by the normal naphthacene suspension emission. D. New absorption bands. Absorption studies at -180°C were made both on the various two hydrocarbohssystems and on the separate components. Under conditions where transfer occurs, a new absopption band appears at 4030 A. for the anthracene solution-naphthacene suspension system and the strong absorption maximum at 5330 A., characteristic of solid naphthacene, disappears (Figure 7). The band at 4030 A. resembles the "charge-transfer" bands which 6,7,123 have been found for the benzene-iodine type of complex 135 and which have been discussed by Mulliken. The new absorption bands for the corresponding chrysene or 1,2,5,6-dibenzanthracene systems are toooweak or lie at too short a wave-length to be detected by the method used. However, the 5330 A. naphthacene band does diminish consider-ably in intensity. E. Studies at -70°C.t at 20°G., and with dry crystals Some systems showing energy transfer were studied in liquid solvents at -70oc> w n e r e t h e phenomenon occurred with a lower efficiency, and at 20°C where the energy transfer was no longer apparent (Figure 3 (c) and (f) ). Another point of interest which will be discussed FIGURE 7 - Absorption of anthracene solution-naphthacene. .suspension transfer • - - • o system at - 180 C. (a) a combined anthracene solution-naphthacene suspension i n EPA showing the new absorption band at 4030 A. - 32 -later i s that no change in the omission of dry naphthacene crystals was observed on the addition of five percent anthracene. III. SYSTEMS WITH ONE COMMENT IN SOLUTION AMD THE OTHER AS  A SUSPENSION, THE FORMER ABSORBING RADIATION OF  LOWER ENERGY THAN THE LATTER. A, New emission and absorption bands The effect of adding to a hydrocarbon suspension a solution of a second hydrocarbon which absorbs radiation of lower energy i s observed in Figures 2 (g), (h); 8,9,10 and 11. For example, the addition of naphthacene solution to a suspen-sion of anthracene, 1,2-benzanthracene, or chrysene at -180°C. causes the naphthacene emission bands to be greatly enhanced i n intensity and to be shifted to longer wave-lengths. (Figures l(s)>(h) and 8) The bands retain the characteristics of the emission from "isolated molecules". Shifts have also been observed for the emission bands of solutions of other hydrocarbons such as anthracene, 1,2-benzanthracene and i t s methyl derivatives, benzo(c)phenan© threne and i t s derivatives, diphenylhexatriene, and phenanthrene (Figures 9,10 and 11). The amount of shift depends both on the hydrocarbon i n solution and on the one in suspension. In Table 2 i s given the positions in A. and the energy in cm."1 of the peak of the highest energy emission band of the solution component i n a large number of these systems. In the last column' of the table i s given the amount by which the highest energy band of the hydrocarbon in solution i s shifted i n the various suspensions. - 33 -FIGURE 8-Emission from systems containing naphthacene solution and a suspension of a second hydrocarbon which ( absorbs at higher energies, in methyl eyclohexane-isopen-tane solvent at - 180°C. Solid curves show naphthacene emission; broken curves show emission from the suspension component. Traces (b) to (t) have the same exposure times while that for trace (a) i s four times as long. (a) naphthacene solution alone (b) to (t) same naphthacene concentration as (a) with the addition of a suspension of (b) acenaphthene (c) 2-methyl anthracene (d) benzene (e) 1,2,-benzanthracene (f) 4T methyl 1,2,-benzanthracene (g) 6 methyl 1,3-benzanthracene (h) 10 methyl l,2,benzanthracene (i) 9,10 dimethyl 1,2-benzanthracene (j) benzo (c) phenanthrene (k.) 3 methyl benzo(c) phenanthrene (1) 6 methyl benzo(c)phenanthrene (m) chrysene (n) diphenylhexatriene (c) naphthalene (p) 2-naphthol (a.) phenanthrene (s) toluene (r) terphenyl (t) trans-stilbene - 34 -FIGURE 8 - 3 5 -FIGURE 9 - Emission from systems containing a solution of anthracene, 2-methyl anthracene, or phenanthrene and a suspension of a second hydrocarbon which absorbs only at higher energies i n a methyl cyclohexane-isopentane solvent at -180°C. A l l traces have the same exposure time. (a) anthracene solution alone (b) to (a) same anthracene concentration as (a) with an added suspension of (b) acenaphthene (c) benzene (d) fluorene (e) naphthalene (f) 2-naphthol (g) terphenyl (h) toluene (i) 2-methyl anthracene solution alone (j) same 2-methyl anthracene concentration as (i) with added naphthalene i n suspension (k) phenanthrene solution alone (1) same phenanthrene concentration as (k) with added naphthalene i n suspension - 37 -FIGUBB 10 - Emission from systems containing a solution of 1,2-benzanthracene or one of i t s alkyl derivatives and a suspension of naphthalene or terphenyl. The solvent i s methyl cyclohexanefrisopentane and the temperature o is - 180 C. A l l traces have the same exposure time. (a) 1,2-benzanthracene solution alone (b) same 1,2-benzanthracene concentration as (a) with added naphthalene i n suspension (c) same 1,2-benzanthracene concentration as (a) with added terphenyl i n suspension (d) 4* methyl 1,2-benzanthracene solution alone (e) as (d) with added naphthalene in suspension (f) as (d) with added terphenyl i n suspension ( 3 ) 6 methyl 1,2-benzanthracene solution alone (h) as (g) with added naphthalene i n suspension (i ) as (g) with added terphenyl in suspension (j) 10 methyl 1,2-benzanthracene solution alone (k) as (j) with added naphthalene in suspension (1) as (j) with added terphenyl in suspension (m) 9,10 dimethyl 1,2-benzanthracene solution alone (n) as (m) with added naphthalene i n suspension (o) as (m) with added terphenyl i n suspension 39 -FISOEE 11 - Emission from systems containing a solution of benzo(e)phenanthrene, one of i t s methyl derivatives, diphenylhexatriene, or trans-stilbene and a suspension of naphthalene or terphenyl. The solvent i s methyl cyclo-hexane-isopentane and the temperature i s - 180°C. The groups of traces (a) to ( i ) , (j) to (1), and (m) to Oo) each have identical exposure times for their members. (a) benzo(c)phenanthrene solution alone (b) same benzo(c)phenanthrene concentration as (a) . with added naphthalene in suspension (c) same benzolc)phenanthrene concentration as (a) with added terphenyl i n suspension (d) 3 methyl benzo(c)phenanthrene solution alone (e) as (d) with added naphthalene i n suspension (f) as (d) with added terphenyl i n suspension (g) 6 methyl benzo(c)phenanthrene solution alone (a) as (g) with added naphthalene in suspension (i ) as lg) with added terphenyl i n suspension CJ) diphenylhexatriene alone i n solution (k) as (j) with added naphthalene i n suspension (1) as (j) with added terphenyl i n suspension (m) trans-stilbene alone i n solution (a) as (m) with added naphthalene i n suspension (o) as (m) with added terphenyl i n suspension - 40 -D D D (b)1 . . I . . . . 1 \ . r \ / . . i , . . \ . . . A **• so A ( e ) * • • . t » IX» 1 1 . . 1 . 1 I \ 4-00 1*. s o A ( h ) . . 1 . . . . 1 A. U.OO t»CO _ i 1 i—1 1 1 11 11 1 1*00 l»SO WOO **•»€> »00 *WO O „ 1 . . . . 1 . .• , » 1 . , J 1 1  ... .. 1 . . . . 1 1 i l l —. . .1 • . . . 1 1. . Coo "no 5oo too -.to 3 " o »»o w o »•.'••> ° A ( m ) ) v \ «l 1 • . 1 1 1 l \ 1 A ( r * il 1 » 1 1 • I • .V A ( 0 ) ISO t o o ISO » o o » lo » o o FIGURE 11 TABLE 2 - Position, energy, and shift of the center of the highest energy emission band of the component in solution in energy, transfer systems where the hydrocarbon.in solution absorbs radiation of lower energy than does the component in suspension. The values were obtained in methyl cyclohexane-isopentane solvent at - 180°C. CUMPOWjiNlT IN SOLUTION COMPONENT AS SUSPENSION HIGHEST SNERGY EMISSION BAND OF SGKJTION . COMPONENT JAnthracene 2-methyl anthracene ft 1,2-benzanthracene Acenaphthene Benzene Fluorene Naphthalene 2-Naphthol Terphenyl Toluene | Naphthalene Naphthalene Terphenyl • POSITION in A. , ENERGY -1 in cm SHIFT -1 in cm 3790 26358 3845 26041 317 3853 25952 •'. 407 V -3925 25478 880 3900 25641 717 3880 25773 585 4010 24938 1420 3830 26109 249 -3860 25907 4000 ] 25000 907 3875 25806 3918 25523 283 3990 25063 743 1' methyl-1,2-benzanthracene 2' methyl-1,2-benzanthracene 5« methyl-1,2-benzanthracene I Naphthalene | Terphenyl Naphthalene Terphenyl ' Naphthalene ? Terphenyl 3892 3960 4040 3880 3940 4100 3860 3905 3980 [ 25694 1 25252 j 24752 | 25773 25380 24390 i |25907 i 25608 j25126 441 942 393 1383 ( i 299 f 781 4' methyl-1,2-benzanthracene 3 methyl-1,2-benzanthracene 4 methyl-1,2-benzanthracene .; Naphthalene \ Terphenyl Naphthalene Terphenyl Naphthalene Terphenyl 3880 3920 4020 3890 3918 3990 3860 3900 3985 I 25773 I25510 I 24876 J j25707 25523 j25063 |25907 125641 !25094 i 263 1 897 184 644 366 813 5 methyl-1,2-benzanthracene n ft | Naphthalene Terphenyl 3860 3900 4010 \ 25907 I 25641 I24938 266 969 6 methyl-1,2-benzanthracene tt Naphthalene Terphenyl 3860 3955 3965 ? 25907 )25284 125220 • 623 I 687 7 methyl-1,2-benzanthracene tt Naphthalene Terphenyl 3890 3955 4020 I25707 1 124876 £23 \ 831 8 methyl-1,2-benzanthracene tt i Naphthalene | Terphenyl 3875 3925 4000 25806 ! 25478 125000 328 806 9 naethyl-1,2-benzanthracene tt It 10 methyl-1,2-benzanthracene TO Naphthalene Terphenyl Naphthalene Terphenyl 3950 4020 4080 3900 3955 4025 25316 24876 24510 25641 25284 24844 ; 440 l 806 \ 357 j 797 10 ethyl-1,2-benzanthracene « 9,10 dimethyl-1,2-benzanthracene ft « benzol c)phenanthrene tt 1 methyl benzolc)phenanthrene « 2 method benzolc)phenanthrene re 3 methyl banzol c)pMasanthrene ft « Naphthalene Terphenyl Naphthalene Terphenyl 2-naphthol Naphthalene Terphenyl Naphthalene Naphthalene Terphenyl Naphthalene Terphenyl 3900 3945 3995 (25641 j25348 325031 •t \ 293 } 610 4030 [24814 4090 ] 24450 4120 | 24272 No transfer of energy 3750 3795 3785 3935 3975 3780 3820 3790 3770 3890 3800 26667 26350 26420 25413 25168 I 26455 \ 26178 I 26385 t! I I 26525 | 25707 i 26316 364 542 317 247 245 I \ \ 277 I 70 ; 818 I 209 4 methyl benzol c)phenanthrene i Naphthalene Terphenyl 3800 3920 3820 i 26316 ) 25510 ! 26178 806 138 5 methyl benzolc)phenanthrene IS tt 6 methyl benzolc)phenanthrene Naphthalene Terphenyl Naphthalene Terphenyl 3780 3810 3815 3800 3835 3820 \ 26455 1 26247 : 26212 ; 26316 \ 26075 f 26178 I 208 • 243 241 138 Diphenylhexatriene Naphthacene Naphthalene 2-napthol Terphenyl 4010 4128 24938 24255 No transfer of energy 4040 \ 24752 Acenaphthene Anthracene 2-methyl anthracene 9,10-dichloro anthracene 1,2-benzanthracene 9,10 dimethyl-1,2-benzanthreicene • ? 4820 10-ethyl 1,2-benzanthracene 1« methyl " 4750 4822 4970 4960 4840 4890 4840 4880 4900 'i 21053 { 20735 ] 20121 } 20161 j 20661 » 20450 i } 20747 | 20661 1 20492 \ 20408 713 186 318 932 892 392 603 306 392 561 645 ft tt tt tt tt tt tt tt phenanthrene tt Trans-stilbene n tt 5 6 7 8 9 10 ti ft re it tt it tt tt tt tt M tt tt tt tt tt n it n tt tt it 4897 4865 4895 4840 » tt n re tt 4900 48S5 ! 4850 coronene 1,2,6,6-dibenzanthracene diphenylhexatriene fluorane naphthalene 2-naphthol pyrene terphenyl toluene trans-stilbene naphthalene naphthalene terphenyl i 4830 4830 benzene benzolc)phenanthrene 1 methyl benzolc)phenanthrene 4822 2 " ' c3 « " 4 tt re 5 « " 6 " " methyl cholanthrene chrysene I 4822 4835 4810 4830 4840 4840 4860 20419 20555 20429 80661 §0S61 20408 20339 805.55 80&9J 20619 20704 20704 20735 20735 20682 20790 20704 20661 20661 20576 no transfer of energy) 4900 j 20408 \ 5040 | 19841 1 no transfer of energy? 4970 { 20121 I 4830 | 20704 j no transfer of energyj 4950 20202 j 4818 20757 I 4870 20534 ! 634 498 624 398 686 498 434 349 349 318 318 371 263 349 392 392 477 3460 3520 3510 3640 3650 28902 28410 28490 27472 27397 645 1212 932 349 851 296 519 492 1018 1093 42 -Hew absorption bands corresponding to the new emission bands have also been observed (Table 5 and Figure 12). B. Efficiency off the Process Quantitative measurements have shown that one part 9 7 of naphthacene i n 3 z 10 parts of anthracene or i n 1.2 x 10 parts of chrysene can be detected i n this way. In some systems where the hydrocarbon i a solution was not a polyacene, the efficiency of the process was somewhat less. At t h i s point, i t i s interesting to note that no measurable fluorescence could be obtained, either from pure pentacene or from pentacene as a crystalline receiver molecule in systems of the type discussed under Results I I . ,However, a b r i l l i a n t red emission was obtained by adding pentacene solution to suspensions of anthracine, chrysene, or, 1,2,5,6-dibenzanthracene. C. Effect of solvent and temperature Changing from the methyl cyclohexane-isopentane solvent to EPA had no significent effect on the occurrence of this process i n a dozen of the systems chosen at random from those studied. The emissions are a l l "short-lived*. T r i a l s at -70°C. and at 20°C. were carried out and i t was shown that even at the latt e r temperature, the shifted solution bands may retain up to twenty percent of their low temperature intensity (Figure 2 ( i ) ). i D. Dry crystals. Dry crystals of hydrocarbons contaminated by small - 43 -TABLE 5- Absorption and emission band maxima for transfer systems containing naphthacene solution and a second hydrocarbon i n suspension at - 180°C. i n EPA Naphthacene solution with Absorption Band maxima in A. Emmission Band maxima in A. Alone Anthracene suspension Chrysene suspension 1,2,5,6-dibenzanthra-cene suspension 4210,4460,4750 4590,4940 4850 4690,4890 4750,5130,5550 4970,5350,5780 4860,5190,5620 4900,5270,5660 EIGrUHS 12 - New absorption bands of an anthracene suspen-sion-naphthacene solution system. (a) anthracene suspension and naphthacene solution in EPA st - 180°C. - 45 7 The new bands are. marked (3) and (4), while (1) and (3) the normal naphthacene solution bands. - 46 -amounts of a second hydrocarbon show emission bands similar to 1 . 4 - v u < * v ,, 16,22,24,25,71,110,117, those which have just been discussed. 118,130,144,145,159,186 _ . ^ .. „ However, in crystals of anthracene the minimum detectable concentration of naphthacene i s about 1 part in 10 , even although a photon multiplier technique more sens-i t i v e than the photographic method available to us was used. Thus the higher quantum yie l d of naphthacene emission i n the suspension system indicates again the presence of an efficient solution-solid energy transfer process. The polyacenes are exceptional among hydrocarbons i n behaving i n this manner. Anthracene also shows up i n trace quantities i n naphthalene or phenanthrene crystals. On the other hand, traces of non-polyacene hydrocarbons in crystals do not usually give as large a fluorescence increase. Another point of interest i s that i f the contamin-5 ating naphthacene concentration rises above 1 part i n 10 parts of anthracene crystals, the band at 5330 A., characteristic of a 117 118 solid naphthacene transfer system appears. » It seems that here the naphthacene molecules are no longer isolated from each other, but are beginning to form aggregates within the anthracene crystal. IV.SYSTEMS CONTAINING- ONLY ONE AROMATIC HYDROCA1B0N COMPONENT In some systems there i s evidence of an energy trans-fe r process from molecules i n solution to suspended particles of the same hydrocarbon (Figures 13-23). A. Systems containing anthracene Figure 13 shows the emission characteristic of dry - 47 -anthracene crystals compared with that of suspensions of anth-o racene alone i n solvents of decreasing polarity at - 180 C. In the most polar solvent (Figure 13 (b) ) the series of sharp bands with a high energy limit at 3770 A., characteristic of anthracene solution, are apparent and mask the weaker emission from the suspended solid. As the polarity decreases, these bands decrease in intensity and are replaced by a new type of emission in the region of the emission bands of the dry solid which are much more diffuse than the la t t e r . In solutions i n the non-polar solvents, without suspended solid, the characteristic solution bands reappear and the emission spectrum looks essentially l i k e Figure 13 (b). In the non-polar suspension i t appears that energy which would have been emitted as "solution bands" has been transferred to the solid.. The diffuseness of the emission may be attributed to variable interaction energy between the dis-solved molecules and the crystal. B. One-component systems of other hydrocarbons An exactly analogous phenomenon, where the suspension emission differs from both the solution and dry solid emissions, i s found i n systems containing 9,10-d,imethyl-l,2-benzanthracene (Figure 16 ( j ) - ( l ) ), benzo(c)phenanthrene (Figure 20 (d)-(f) ), chrysene (Figure 14), or 1,2 5,6-dibenzanthracene (Figure 22 (d)-(f) ). In some cases such as 1,2-benzanthracene (Figure 16 (g)-(i) ), methyl 1,2-benzanthracene (Figure 18 (a)-(c) ), or naphthacene (Figure 23.(a)-(c) ) the emission from the FIGURE 13- Self trans-fer i n anthracene (a) Emission from dry anthracene cry-stals at - 180°C. (b) Solution of anth-racene containing excess suspended anthracene cry-stals i n 12 ml. of isopentane-methyl cyclohexane with 0.6 ml. of ethanol added to increase the sol-vent polarity (£) as (b) with only 0.1 ml. of ethanol (d) as (b) with no added ethanol The nsolution"bands have,disappeared and have been replaced by a : . continuum different -fro-m the emission of dry crystals or solutions. The "Solution" bands reappeared i n (d) when the suspended solid was removed. 380 4 0 0 450 500 ; , , - 4 9 -suspension i s similar i n position and form to that from the dry-crystal except that the highest energy band may have a slightly greater relative intensity i n the suspension. As the emission from the hydrocarbons i n solution and that from the dry crystal-l i n e material have comparable intensities; and as only emission characteristic of suspension i s obtained from systems containing so l i t t l e suspended material that i t cannot readily be seen, i t seems that this pehnomenon i s analogous to the energy transfer process already described for anthracene. In a l l the solvents used, suspensions of hydrocarbons such as 9,10 diphenyl anthracene (Figure 16 (a)-(c) ), coronene (Figure 22 (a)-(c) ), or pyrene (Figure 23 (d)-(f) ) show emission bands identical to those of the solution along with a weak emission from the suspended substance. Thus, in these systems there i s no apparent energy transfer from the molecules in solution to the suspended material. The results of these studies are summarized 14 Table 4 and traces of the fluorescence from the various solutions, suspensions, and dry crystals are given i n Figures 14 to 23. Emission bands characteristic of the solution were shown by suspensions of a l l the hydrocarbons, except possibly 2-methyl anthracene, i n a more "polar" solvent containing 0.5 ml. of ethanol i n 6.0 ml. of methyl cyclohexane-isopentane. At 20°C. energy transfer phenomena of t h i s type were found to cease entirely. Studies on the emission of one-compenent systems of hydrocarbons such as naphthalene, terphenyl, or acenapbthene whose emission l i e s in the region of 3200 to 3500 A . were not TABLE 4 - Rroperties of tfa® emission of suspensions of a single aromatic hydrocarbon in methyl cyclohexane-isopehtane solvent at - 180°C. Systems marked wit& a * are those whose solution, suspension, ^ and dry crystals have emission of the same form.  Hydrocarbons i n whose suspensions energy transfer i s found Suspension emission differs from that of the crystals Anthracene 9,10 dibromo-anthracene 9,10 dichloro-anthracene 9,10 dimethyl~an thrac ene 1'methyl-1,2-benzanthracene 2 »methyl~l,2-benzanthracene 3 methyl-1,2-benzanthracene 4 methyl-1,2-benzanthracene 5 methyl-1,2-benzanthracene 9 methyl-1,2-benzanthracene 10 methyl-l,2-benzanthracene 10 ethyl-1,2-benzanthracene 9,10 dimethyl-1,2-benzanthracene benzo(c)phenanthrene 2 methyl-benzo(c)phenanthrene 4 me thyl-b enz o(c)phenanthrene 5 methyl-benzo(c)phenanthrene 6 methyl-benzo(c)phenanthrene chrysene 1,2,5,6-dibenzanthracene diphenylhexatriene trans-stilbene Suspension emission i s similar to that of the crystals 2-methyl anthracene 1,2-benzanthracene 3 ?methyl-ls2-benzanthracene 4'methyl-1,2-benzanthracene 7 methyl-1,2-benzanthracene 3 methyl-benzo(c)phenanthrene | naphthacene Hydrocarbons i n whose suspensions no energy transfer i s found * 9,10, d i - 0> -naphthyl anthracene 9,10 diphenyl anthracene * 6 methyl-1,2-benzanthracene 8 methyl-l,2-benzanthracene j*' 1 methyl-benzo(c)phenanthrene C | coronene J* fluoresithene \ pyrene I " . . 51 -l O o I . O M-OO 1 A A 3feO 3S»0 **-00 C b ) U-50 FIGURE 14 - Self trans-,f fer in chrysene (a) emission from dry chrysene crystals at - 180°C. (b) emission of a chry-sene suspension i n methyl cyclohexane-isopentane. The spec-trum shows a trend towards the contin-uum found for anth© racene under similar conditions. The "solution" bands are also missing, (c) emission of chry-sene i n methyl cyclohexane-i sopen-tane solution - 52 -FIGURE 15 - Emission from one-component hydrocarbon systems at - 180°C. A l l solutions and suspensions are in methyl cyclohexane-isopentane solvent. 9,10 dibromo-anthraeene i n (a) solution (b) suspension (c) dry crystals 9,10 dichloro-anthracene i n (d) solution (e) suspension (f) dry crystals 9,10 dimethyl-anthracene i n (g) solution (h) suspension (i) dry crystals 9,10 di-^-naphthyl-anthracene in (j) solution (k) suspension (1) dry crystals I. J) D D o a b 1 1 i i i 1 I i i r 1 I I I 1 c. 5 M-OO W-SO S O O A d R • i / . i i i i > i 11\i 111 M-OO 4-50 500 e i 1 i i^-i i 1 i i i i 1 i i t i Hoo 4.S"0 SOO f i I i i ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ > 4 -00 4-SO 5 0 0 9 , y i , , . , i , . . \ i . 111 if OO - 4 S O 5 0 0 h . • 1 i y i i 1 i i i i 1 i i 11 4 - 0 0 U-SO SOO I 1 1 • 1 U-oo M-5o 5 o o j ' ^ ^ ^ ^ ^ ^ ^ ^ S v ^ ^ ^ ^ 1 1 1 1 l»-0 0 4-SO SOO K UOO M-BO SOO 1 1W50 'VSO SOO ' • " O 0 **-SO S O O 'fOO " S O S O O FIGURE 15 - 54 -FIGURE 16 - Emission from one-component hydrocarbon systems at - 180°C. A l l solutions and suspensions are in methyl cyclohexane-isopentane solvent. 9,10 diphenyl anthracene in (a) solution (b) suspension (c) dry crystals 2 methyl anthracene in (d) solution (e) suspension (f) dry crystals 1,2,benzanthracene i n (g) solution (h) suspension (i) dry crystals 9,10-dimethyl 1,2-benzanthracene in (j) solution (k) suspension (1) dry crystals / FIGURE 16 - 56 -FIGURE 17 - Emission, from one-component hydrocarbon systems at - 180°C. A l l solutions and suspensions are in methyl cyclohexane-isopentane solvent. 10-ethyl 1,2-benzanthracene i n (a) solution (b) suspension (c) dry crystals 1 T methyl 1,2-benzanthracene i n (d) solution (e) suspension (f) dry crystals 2* methyl 1,2-benzanthracene in (g) solution (h) suspension (i) dry crystals 3' methyl 1,2-benzanthracene in (j) solution (tc) suspension (1) dry crystals - 58 -FIGURE 18 - Emission from one-component hydrocarbon systems at - 180°C. A l l solutions and suspensions are in methyl cyclohexane-isopentane solvent. 4' methyl 1,2-benzanthracene in (a) solution (b) suspension (c) dry crystals 3 mpthyl 1,2-benzanthracene in (d) solution (e) suspension (f) dry crystals 4 methyl, 1,2-benzanthracene in flg) solution (h) suspension (i ) dry crystals 5 methyl 1,2-benzanthracene (j) solution (k) suspension (1) dry crystals - 60 -FIGURE 19 - Emission from one-component hydrocarbon sustems at - 180°C. A l l solutions and suspensions are in methyl cyclohexane-isopentane solvent. 6 methyl 1,2-benzanthracene i n (a) solution (b) suspension (c) dry crystals 7 methyl 1,2-benzanthracene i n (d) solution (e) suspension (f) dry crystals 8 methyl 1,2-benzanthracene i n (g) solution (h) suspension (i) dry crystals 9 methyl 1,2-benzanthracene (j) solution (k) suspension (1) dry crystals - 62 -FIGURE 20 - Emission from one-component hydrocarbon systems at - 180°C. A l l solutions and suspensions are i n methyl cyclohexane-isopentane solvent. 10 methyl 1,2-benzanthracene in (a) solution (b) suspension (c) dry crystals beazo(c) phenanthrene in (d) solution (e) suspension \f) dry crystals 1 methyl benzo(c) phenanthrene (g) solution (h) suspension (i) dry crystals 2 methyl benzo(c)phenanthrene in (j) solution (k) suspension (1) dry crystals - 64 -FIGURE 21 - Emission from one-component hydrocarbon systems at - 180°C. A l l solutions and suspensions are in methyl cyclohexane-isopentane solvent. 3 methyl benzo(c)phenanthrene in (a) solution (b) suspension (c) dry crystals 4 methyl henzo(c)phenanthrene i n (d) solution (e) suspension (f) dry crystals 5 methyl benzo(c)phenanthrene in (g) solution (h) suspension (i) dry crystals 6 methyl benzo(c)phenanthrene in (j) solution (k.) suspension (1) dry crystals - 66 -FIGURE 22 - Emission from one-component hydrocarbon systems at - 180°C. A l l solutions and suspensions are i n methyl cyclohexane-isopentane solvent, coronene in (a) solution (b) suspension (c) dry crystals 1,2,5,6 dibenzanthracene i n (d) solution (e) suspension (f) dry crystals diphenylhexatriene in (g) solution (h) suspension (i) dry crystals fluoranthene in (j) solution (k) suspension (1) dry crystals - 67 -D o D i a k. , , . / b \ t • • . • 1 • .Vi c —1 1 ,1 1 ^^^^^^^ > 'tee WO S o o 1 A d W 1 , , , , 1 i T V i 1 i i i w HOO / 1 . . • I»SO 5oo Ik • 1 i i i i 1 i i i i UOO 1+50 SOO A , A , , i .1 i i i i 1 i i i J _ D M-OO M-TO SOO ^ i # 1 • i l I I i i l l l H O C 4-50 Soo hi 1 , / 1 i 1 i i i i 1 i i i i U-oo U-So Soo I 3 14-00 '••so s o o J 31 i A i i i i_J i_j • . 1 i i i i wo i+so s oo K i x i — i — i — i i i i •' i ' ' ' i UOO U-SO 500 1 1 IfOO i+so Soo l+OO U S O S O O U-OO 1+SO S O O FIGURE 22. - 68 -FIGURE 25. - Emission from one-component hydrocarbon systems at - 180°C. A l l solutions and suspensions are in methyl cyclohexane-isopentane solvent, naphthacene in (a) solution (b) suspension (c) dry crystals pyrene in (d) solution (e) suspension (f) dry crystals trans-stilbene i n (g) solution (h) suspension (i) dry crystals - 69 -- 70 -carried out as i t was impossible to obtain an intense and absolutely monochromatic Hg 3130 A. as an irradiating source. DISCUSSION I. SYSTEMS WITH TWO HYDROCARBONS IN SOLUTION Our failure to detect any appreciable energy transfer in the systems containing only dissolved molecules does not contradict the work of Forster. It has already been noted that the very low solubility of aromatic hydrocarbons at -180°C. in the solvents used severely limited the concentrations with which we could work. In EPA the approximate concentrations attainable at - 180°C. are for anthracene 3.56 x 10 moles per l i t e r , for -4 chrysene 1.18 x 10 moles per l i t e r , and for naphthacene 1.54 -5 X 10 moles per l i t e r . Thus in an anthracene-solution -naphthacene solution system the average distance between the solute molecules i s 165 A., while i n a chrysene-naphtnacene system the average distance i s 232 A. These, distances are considerably greater than the maximum of 60 A. over which Forster found interaction between molecules of trypaflavin 54-57 and rhodamine B. However, we have shown that on ultra-violet irrad-—2 iation of ta xylene solution of terphenyl (1.30 x 10 moles per' -5 l i t e r ) and diphenylhexatriene (4.31 x 10 moles per l i t e r ) at 20°C. there i s no evidence of energy transfer. Forster reports indirect evidence of a definite energy transfer i n a methanol-—3 HCI solution of trypaflavin (1.0 x 10 moles per l i t e r ) and -4 rhodamine B (4.0 x 10 moles per l i t e r ) Inder similar irrad-iation conditions. Thus i t appears that there i s a much more - 71 -efficient energy transfer in solution between aromatic molecules with polar substituents than between different aromatic hydro-carbons . II. INTERACTION MECHANISM FOR HYDROCARBON SOLUTION-SUSPENSION SYSTEMS . A. Influence of solvent The possible interaction mechanisms for the systems in which energy transfer has been found, w i l l now be considered. Although the solvent influences the transfer process, i t remains throughout in i t s ground state as the incident radiation (max-imum energy used was 40,000 cm"1 ) i s insufficient to excite i t . B. Possible, "energy transfer"mechanisms Thus the possible mechanisms are: 1. Reabsorption of the energy donor's emission by the acceptor substance. 2_. Transfer from one component of a molecular complex to another component 3. Long-range dipole-dipole interactions of the type predicted by Forster 4. "Resonance transfer" of energy between identical molecules, before the excited molecule loses i t s vibrational energy. It w i l l be noted that the interaction term in For-54-57 ster's expression for the probability of energy transfer i s zero unless the emission band of the donor overlaps the absorption band of the acceptor. This i s a consequence of the -assumption that the energy transfer process, like the emission - 72 -of radiation, i s slow compared with the rate at which vibrational energy is lost, so that both processes occur from the lowest vibrational level i n the excited electronic state (Figure 24). Since this i s hot the case i n process 4, the latter must be considered separately from type 3. Furthermore, since complex formation may involve orbital overlap, or even electron transfer, the mechanism for type 2_ may be quite different -f»eiiithat involved in any long-range process. C. Evidence for a non-radiative process In the three types of system i n which energy transfer has been found, the emission region of one component overlaps, at least i n part, the absorption of the second component. Thus, the possibility of energy transfer by means of a reabsorption of the energy donor's emission must not be overlooked. However, that this mechanism i s unimportant i s shown by the following observations. 1. Equal weights of anthracene and naphthacene were dissolved i n EPA and i n methyl cyclohexane-isopentane-ethanol so that at - 180°C. the anthracene remained i n solution i n both solvents, while the naphthacene formed a suspension i n the second solvent but remained in solution i n the EPA. Transfer was detectable only when micro-crystalline naphthacene was present (Figure 25). This, and the observation that naphthacene solution and dry crystals have almost identical absorption coef-fi c i e n t s in the region of the anthracene solution emission (wavelengths up to 4800 A.) (Figure 26) indicates that transfer does not occur by the reabsorption of anthracene emission by - 73 -FIGURE 24- Potential energy curves for ground and excited states of a molecule. K represents the energy available for transfer i f the process i s more rapid than v i b r a t i o n a l deactivation and i s i d e n t i c a l with the absorbed energy. J represents the energy available for processes slower than v i b r a t i o n a l deactivation such as emission of rad i a t i o n . ENERGY T —-> FIGURE 25. - Effect of the state of aggregation of the receiving substance on transfer efficiency at - 1 8 0 ° C . (a) anthracene and naphtha-cene in solution in EPA (b) amounts of anthracene and naphthacene ident-i c a l with those in (a) methyl eyclohexane-isopentane-ethanol sol-vent. The anthracene i s again i n solution while the naphthacene i s i n a micro-crystalline sus-pension. The exposure time i s the same as that of (a) . (c) as (b) with the expos-ure time reduced twenty-fold. • Broken lines indicate anthracene emission; solid lines naphthacene emission - 75 -FIGURE 26 - Transmission measurements of naphthacene. Solid line-sublimed on glass; broken line-in 1-bromo-naphthalene. naphthacene microcrystals. 2_. Further evidence for a non-radiative process comes from the observation that the transfer does not produce the aame intensity increase in a l l the vibrational bands of the acceptor molecule. (a) Transfer from various hydrocarbons in sol-ution to naphthacene suspension produces an intensity increase in what appears to be a slightly shifted- 0-0 band. (b) Transfer to anthracene suspension produces the greatest intensity increase in the highest energy suspension band. (c) In systmms containing various hydrocarbon suspensions and a solution of a hydrocarbon which absorbs lower energy radiation, the transferred energy is emitted in a set of banfis displaced by up to 200 A. from the normal hydrocarbon solution emission. (d) In many of the systems in which energy is transferred from molecules in solution to microcrystals of the same substance, the resulting emission shows slight shifts in band positions or slight differences in the rel-ative band intensities when comparisons with the emission of dry solid are made. The emission of the donor substance usually suffers the same intensity decrease in a l l the vibrational bands, rather than a decrease only in the region where i t overlaps the absorp-tion bands of the acceptor substance. - 77 -3.Substances such as anthracene and 1,2-benzanth-racene have almost Identical regions of emission. A solution of the former gives rise to an efficient energy transfer to naph-thacene suspension, while with a solution of the latter hydro-carbon there is no analogous transfer. 4. The occurrence of transfer depends on the sol-vent even u".though there are no marked differences in the hydrocarbon absorption in the solvents that were used. 5. Additional absorption bands appear in the trans-fer system. 6_. The great decrease in transfer efficiency at 20°C. is not comparable with the relatively small change in the absorption coefficients in going from - 180°C to 20°C. Thus i t appears that the observed energy transfer processes do not proceed by a simple absorption, emission, reabsorption, re-emission process. D. Evidence for complex formation 1. Varying the solvent polarity does not change the interaction energy in a continuous manner. As the solvent polarity falls, the interaction between molecules in solution of anthracene, chrysene, or 1,2,5,6-dibenzanthracene and the naphthacene micro-crystals shows a sudden appearance after which i t remains approximately constant. 2_. New absorption bands appear in the transfer systems. Thus the formation of a molecular complex, and conse-quent short-range interation are suggested. If the solvent - 78 -molecules are more polar than the inductively polarized hydro-carbon molecules, preferential adsorption of solvent on the crystal surface occurs, and hydrocarbon complex formation i s prevented. A similar type of complex is formed in systems where there i s apparent energy transfer from micro-crystals of one hydrocarbon to dissolved molecules of a second compound. III. MPORTAKTCB OF MICRO-CRYSTALS The increased efficiency of micro-crystals over sin-gle molecules as one component of a transfer system i s presum-ably due to "aflsorption" ( i . e . the binding force between the single molecule and the cyrstal i s greater than that between two single molecules). The lack of single molecule transfer indicates that the inter-molecular attractive forces are so weak that even at - 180°C. they are largely overcome by thermal agitation. This suggests that the energy of such single-pair attraction cannot be much greater than 50 calories/mole. However, since transfer i n systems with micro-crystals i s s t i l l readily discernable at 200°E., the "adsorption force" between the interacting molecules and micro-crystals must be at least 500 calories.per mole. In view of the behaviour of hydrocarbon-aromatic 152 nitro compound complexes i n solution, i t seems probable that at lower temperatures than those available to us, complexes between hydrocarbon molecules in solution might be stable, and. transfer would be observable. IV. ENERGY TRANSFER IN SOLUTION BETWEEN IDENTICAL MOLECULES A. Evidence for energy transfer bwtween identical molecules - 7 9 -1. Systems with, one hydrocarbon Since solution fluorescence disappears in transfer systems containing only a suspension of one hydrocarbon, there must be a succession of energy transfers from one molecule in solution to another with a f i n a l transfer So the microcrystal. As the emission band of the transfer system i s not always exact-l y identical with that of the dry crystals 3 or with the sum of that from dry crystals and solution, the last step probably involves the formation of a type of complex in which there is an oriented surface layer of molecules not packed in the same way as in the crystals. 2. Systems with two hydrocarbons In systems with energy transfer from hydrocarbon "A" in solution to micro-crystals of a second compound "BM, the decreased emission intensity of the component in solution and the very intense emission from the complex suggest that energy passes from one "A" molecule to another in solution. Finally the energy i s passed to an "A" molecule which is adsorbed onto a micro-crystal of "B" to give a complex of the type already described. As the emission of dry naphthacene crystals i s unchang-ed by the addition of five percent anthracene, the new emission bands obtained in such systams are properties of the adsorption complex. B. Solvent Effect It has already been shown that transfer from anth-racene in solution to micro-crystals of naphthacene occurs with an apparently equal efficiency i n EPA and in methyl cyclohexane-... :: ... . „• .: ,: - 80 -.. , . . ... isopent&ne, while transfer-from, anthracene in solution to anthracene microrcrystals occursv.onjy i n the latter solvent. This indicates that an increasingly polar solvent eliminates the transfer process by becoming preferentially adsorbed to the crystal surface rather than by eliminating the "resonance transfer" of energy between identical molecules in solution. C. Significance of these observations 1. In solid systems Energy transfer i n solution thus occurs quite readily between identical bydrocarbon molecules, while under similar conditions no transfer between different hydrocarbon molecules i s observable. This leads-"to the important conclusion that strong overlap of the emission region of the donor molecule and the absorption region of the acceptor molecule i s not essential. Therefore "resonance transfer" of energy between identical molecules, before the excited molecules loses i t s vibrational energy i s more important than long-range dipole-dipole inter-actions under the conditions of our experiments. Thus, for these systems, Forster?* expression for 134 the probability of energy transfer should be modified. The results obtained show that the transfer process may be flast enough to compete with vibrational deactivation, which may be quite slow in the solid state at - '180°C. Reference to Figure 24 shows that here we have process "K" rather than process " J " which Forster predicted. 2. In l i q u i d solution - 81 -Systems at - 70°C. show only energy transfer of the type found for systems at -.180°, even though at the higher tem-perature the solvent i s li q u i d , thus making the loss of vibrat-ional energy i n the excited state more probable (Figure 24} ' The following argument provides an explanation as to why the transfer occurs from one molecule to an identical mole-cule rather than to a second kind of molecule with an excited state of lower energy. For any excited molecule the highest transfer prob-a b i l i t y i s to i t s nearest neighbor which, in turn, w i l l transfer the energy to i t s nearest neighbour. This leads to excitons diffusing along concentration gradients u n t i l the energy i s thrown between a pair of molecules that are closer to each other than to any of their nearest neighbours. The modern theory of liquids postulates that i n solutions there i s a series of semi-ordered areas where incipient crystallization begins. An exciton "buries" i t s e l f i n such an area which tends to exclude molecules of a second substance, B, unless they actually form a complex. As the nearest B molecule i s far away there i s only a small probability of energy transfer to i% before the molecule of the f i r s t substance emits i t s energy as radiation. The only definite eheck on this theory i s that the solution spectra should become different from that of isolated molecules at average intermolecular distances. Compounds such as anthracene show a continuous lowering of the energy of their absop^stion and emission bands in going from vapour to solution to dry c r y s t a l s . 8 7 ' 1 0 7 ' 1 6 6 - 82 -Y. MECHANISM OF TRANSFER FROM SUSPENSIONS OF ONE HYDROCARBON TO SOLUTIONS OF ANOTHER A. Transfer process in suspensions. Although, energy transfer from a suspension of one hydrocarbon "C" to dissolved molecules of a second "D" definitely involves the formation of an "adsorption complex", the details of the process diff e r slightly from those fur the other types of systems which are discussed i n the preceding section. 1. The occurrence of this "C" to "D" transfer process does not depend on solvent polarity. 2_. In methyl cyclohexane-isopentane solvents this transfer of energy i s usually accompanied by a considerable decrease in the fluorescence intensity of "C" which i t s e l f i s usually subject to a "self-transfer" phenomenon. 3_. In EPA where the "self transfer" for "C" no lon-ger occurs, there i s usually a smaller decrease in the fluor-escence of "C" in "C" to "D" transfer systems. Thus in this process the transferred energy i s that which i s either absorbed directly by the micro-crystals, or i s transfered to them by a "self-transfer process". B. Transfer process i n dry crystals. Under "Results", page 42, i t i s noted that dry cry-stals of "C" containing "D" impurity show the same emission bands as these transfer systems, but that in the latter case much smaller amounts of naphthacene can be detected. The transfer process occurring in the impurity cry-stals may. be explained i f the matrix and impurity are assumed to form a type of conducting system. In the solid state the - 83 -orbitals of the excited electrons slightly overlap those of the adjacent molecules. Thus excitation energy absorbed by any part-icular molecule can be passed along by a process analogous to the flow of an electric current by the displacement of electrons. Finally the energy would be dissipated as radiation. If an im-purity molecule is present, i t can accept energy from the matrix molecules, and emit i t as light. The interaction of the impurity molecule electron orbitals with the matrix orbitals leads to a shift of electronic energy levels, and a consequent shift of both absorption and emission energy levels. C t | Reason for increased transfer efficiency One possible explanation for the increased transfer efficiency in our suspension systems i s that the impurity cry-stals formed on rapidly cooling the system to -180°C. are less perfectly formed so that there i s a possibility, on excitation, of a greater overlap between the orbitals of the matrix and impurity molecules than there i s in the large, slowly formed crystals which are used in the studies 'of dry crystals. VI. CORRELATION OF COMPLEX FORMATION AND HYDROCARBON PROPERTIES . Once the occurrence of these energy transfer processes was established, an examination of a great many hydrocarbon systems was made in order to try to determine the properties necessary for the process to take place. A. Systems with transfer from molecules i n solution to micro-cyrstals 1. Systems with two different hydrocarbons In systems where there i s energy transfer from dis-- 84 -solved molecules to micro-crystals of a second hydrocarbon, complex formation is apparently dependent on the magnitude of the dipole induced i n the hydro-carbon molecule compared to the dipole of the solvent. Consequently, i t should be possible to arrange hydrocarbon molecules in order of decreasing ease of polarizability of theirTT-electron system on the basis of transfer efficiency. 30-32 37 64 An extensive literature search was made ' ' ' 65,77,79,148-150,156,182 . ... . . . , . . ' ' ' ' ' and the values of bond orders and free valences calculated by the methods of molecular orbitals, valence bond, and "e'tats de spin" were tabulated. However, no particular value of free valence associated with high adjacent bond orders could be correlated with the ease of complex formation. (a) The method of "etats de spin" gives a maxi-mum "indice de valence l i b r e " S 1 . 3 2 . ^ 2 0 f 0.472 surrounded by bonds with "indices de liasio n " of 0.478 and 0.272 for acenaph-thene at positions 2 and 4, chrysene at position 1, fluoranthene at position 4, naphthalene at position 1, perylene at position 1, phenanthrene at position 1, and pyrene at position 3. Of these phenanthrene complexes with naphthacene suspension i n both EPA and loss polar solvents; chrysene complexes with naphthacene only in the less polar solvents; and naphthalene complexes with anthracene suspension. The other compounds l i s t e d form no such complexes. (b_) Valence bond calculations give the 10 - posit-ion of both anthracene and 1,2-benzanthracene an "indice de valence" greater than 0.25 with adjacent "indices de liasio n " 37.148-150 of 0.60 to 0.80. * However, only the anthracene - 85 -complexes with, the naphthacene suspension. (cj The value of the maximum electron density at any atom of the highest occupiedTT-orbital of the ground state of the raolucule i s 0.387 for anthracene, 0.333 for benzene, 0.177 for benzo(c)phenanthrene, 0.297 for chrysene, +.295 for naphthacene, 0.362 for naphthalene, 0.240 for pery-lene, 0.344 for phenanthrene, and 0.272 for pyrene. Complexes stable in EDA are formed between molecules of anthracene or phenanthrene and naphthacene suspension. The complex with chry-sene molecules i s stable only in non-polar solvents, while no complex with naphthacene suspension i s obsrved for the other molecules which are l i s t e d . However, on the basis of this argu-ment we should expect a complex between molecules of naphthalene or benzene and micro-crystals of naphthacene. A complex i s formed between molecules of naphthalene and micro-crystals of anthracene. ThuSj no satisfactory explanation of the properties required for complex formation of this kind could be found. 2. One-component systems Likewise, no theory could be devised to account f o B the occurrence and non-occurrence of energy transfer in systems of one hydrocarbon (Table 4). From the available data i t i s impossible to.decide whether the lack of apparent transfer i s due to a break-down of resonance transfer between the solution molecules, or to a lack of "adsorption1* complex formation. It should be mentioned that studies of this kind were complicated by the necessity of having absolutely pure hydrocarbons (Appendix - 86 -1), and thus the results for some compounds could not be recorded. B.Systems with transfer from micro-crystals to molecules in solution In systems of this kind i t seems l i k e l y that the amount in cm "Say which the solution bands are shifted would give a measure of the interaction in forming the complex between the dissolved and micro-crystalline components. However an examination of the results in Table 2 f a i l e d to reveal any relationship betwemthe shifts and elect-ron densities or bond orders of the molecules. The irregularities in the shifts are ill u s t r a t e d by the fact that the solution bands of benzo(c)phenanthrene, i t s mono-methyl derivatives, diphenylhexatriene, and naphthacene are a l l shifted more in naphthalene suspension than in terphenyl suspension. The solution bands of anthracene, 1,3-benzanthracene, i t s methyl derivatives, and trans-stilbene have a greater shift in the terphenyl suspen-sion. It was noted that there i s a f a i r l y good inverse relationship between, the shift of the naphthacene solution bands and the carcinogenic activity of the particular 1,2-benzanthracene forming the suspension (Table 5). In the table are also given the se l f - p o l a r i z a b i l i t i e s , which up to the present time have given the best theoretical correlation with biological a c t i v i t y of this series of compounds. The correlation between biological activity and the shift of the naphthacene bands i s poorer for the benxo( c)phen-anthrene series. This may be accounted for by the smaller d i f -TABLE. 5 - The shift of the highest energy naphthacene solution band at - 180°C. In suspensions of various hydrocarbons compared with the carcinogenic activity and self-polar-i z a b i l i t y values, at the particular substituent position COMPONENT IN SUSPENSION • 1APHTBACENE ACTIVITY SELF-SOLUTION POLARIZ-SAND SHUT ABILITY Ref .301, 332 1,2-benzanthracene e ,603 cm 1 0 9,10-dimethyl-i.2-benzanthrace ie 306 n .+ -L- _L_ 10-ethyl t i . ft 392 tt "T^  T -T-1' methyl IT ft 561 tt 0 .439 2 » " It w 645 tt 0 .410 3 ' '! tt i t 634 tt 0 .404 4* n ft i t 498 tt 0 .439 3. •» ft tt 624 tt +- .448 4 » ft tt 392 tt .447 5 " tt t i 392 tt .452 6 s tt 645 n •+ .409 7 «?, tt tt 686 n -t- .410 8 » ft tt 498 i t -+• .449 9 1 ft i t 561 i t ++ .496 10 ? tt tt 434 tt .514 Benzo ( c} phenanthrene 349 tt +-1 methyl benzo( c)phenanthrene 318 tt . - - • 2 " tt 318 tt -+- + 3 ? It 371 tt -t- + 4 •» tt 263 n - H + 5 «! It 349 tt + 6 M ft 392 « + + 20-methyl cholanthreije 392 n -t- + + + 1,2,5,6-dibenzanthracene 645 tt acenaphthene 318 ft 0 "Benzene 349 i t 0 chrysene 477 tt 0 terphenyl... 851 t i 0 toluene 296 i t 0 - 88 / ference in activity of the members of this series. However, any relationship.of this kind breaks down entirely when one compares hydrocarbons with different basic ring structures. VII. . GENERAL TOISLUSIONS For systems of aromatic hydrocarbons at -180°C. i t has been found that "resonance transfer" of energy between identical molecules in solution may occur, but that transfer between different molecules does not occur. "Adsorption comp-lexes" of hydrocarbon molecules on micro-crystals of the same or of a different hydrocarbon occur spiite often. These in many ways resemble the Tf -electron complexes which are discussed in the Introduction. However, no satisfactory theory can be advanced to relate the ease of complex formation and the properties of the hydrocarbon molecules. Several factors such as electron density, polarizability, and steric effects may be important. As a f i n a l step the va l i d i t y of Forster's work was checked by studying solutions of trypaflavin and rhodamine B at 54-57 20°C. The increased quenching iBf trypaflavin emission on adding greater concentrations of rhodamine B was observed. However, i t i s f e l t that Forster does not cite sufficient evid-ence to allow him to eliminate the possibility of complex for-mation between the dissolved components. VIII. TRIPLET STATES It should be mentioned that i n the studies on two-component hydrocarbon systems only changes in the fluorescence . „ . , 97,113,114,120,121 spectrum were studied. Previous workers ' ' ' ' - 89 -have shown that most aromatic hydrocarbons possess a fluorescence —8 with a h a l f - l i f e ^ o f approximately 10 seconds; and a phosphor-escence with a h a l f - l i f e of several seconds. In some cases the fluorescence and phosphorescence overlap, and usually the phos-phorescence i s much waaker. Thus, even.: •'...though no changes in the phosphorescence intensity were observed, a several-£o2Ld increase might, in some cases, have remained unobserved. As yet, there has not been sufficient time to make a detailed study of these possible int-ensity changes which would involve many exposures of several hours each, taken by the method described in "Expermental Method". However, a translation of a recent Russian paper1-7-1-reports sn increase in the naphthalene t r i p l e t emission at -180°G. on the addition of benzaldehyde, which absorbs lower energy radiation. It i s obvious that the workers were not aware of the possible importance of micro-crystals. When time permits, additional work w i l l be undertaken to see whether this pehnomenon occurs when the two substances are in true solution and whether i t occurs when both dissolved substances are hydrocarbons. -The t r i p l e t levels for some of the hydrocarbons studied which have not yet been reported in the literature are recorded i n Appendix 3. IX. PROPOSALS FOR C0NTII\1UATI0H OF THE WORK Succeeding work on this problem should aim to obtain . more quantitative results than were possible with the methods - 9 0 -used. Values of absolute quantum yield in the different systems 3 75 under varying conditions are essential ' It i s possible that the failure to find complexes i n many of the systems may be due to a quenching of emission which has been found to occur in 125 some systems containing heterocyclic molecules . Thus a means of obtaining accurate low-temperature absorptions would be most h e l p f u l . 1 1 9 * 1 7 0 Studies of possible complex formation in sys-tems containing hydrocarbons which absorb similar energy rad-iation would be useful in finding a more definite relationship between systems where the suspension component absorbs radiat-ion of lower energy than the component in solution and systems where the component in solution absorbs lower energy radiation than the suspension. As investigation of the possible photoconductivity in crystals of aromatic hydrocarbons 1 2' 1 7 8would help elucidate the function of the micro-crystals. .Lifetime and depolarization s t u d i e s 1 4 2 would aid in t&e understanding of resonance trasnfer in solution. The importance of t r i p l e t states in energy transfer mechanismi 0 6 , 1 7 1has been pointed out i n the previous section. APPLICATION OF RESULTS OBTAINED  I. GENERAL APPLICATIONS A wider recognistion of "dispersion force" complexes might help to explain a wide variety of phenomena, especially i n the biochemical f i e l d . The extreme d i f f i c u l t y encountered i n the preparation of hydrocarbons absolutely free of each other (Appendix 1) doubtless results from the formation of such com-plexes. Fluorescence quenching may also be satisfactorily - 91 -explained by such complex formation (Introduction, pages 3 and 4). In fact, many instances of apparent quenching may involved the formation of complexes which emit in the infra-red. There also arises the question as to whether or not energy transfer i n vapour pftase mixtures, such as benzene and aniline, (Introduction, page 6) and in the dye solutions studied by Forster (Introduction, pages 6 and 7) may involve complex formation and consequently intermolecular distances smaller than those calculated by simple concentration arguments, rather than the previously postulated long range dipole-dipole forces. II. APPLICATION TO THE PROBLEM OF CARCINOGENESIS Many of the polycyclic hydrocarbons mentioned in the previous sections are carcinogenic, and thus i t was f e l t that the techniques here developed might be applied to the dejection of very small amounts of carcinogenic compounds or their deriv-atives i n animal tissue. A detailed literature survey, involving almost one hundred references, of the work done in an attempt to elucidate the mode of reaction of carcinogen&fc hydrocarbons inside the body of an animal i s given in Appendix 4. ,A. Experimental work with human tumor tissue As many compounds show an increased fluorescence intensity at - 180°C, i t was f e l t that i t might be possible to detect a compound characteristic of tumor tissue. Samples of human tumor tissue and the corresponding normal tissue, removed in surgical operations, were examined. However, i t was found that the emission of any compound for which we were looking was - 92 -y obscured by the very bright fluorescence at 4000 to 5000 A. of the sedatives such as morphine, sodium pentathol, sodium nembutal, and sodium secconal which were administered prior to and during the operation; B. Experimental work with mice Thus i s was decided to try to follow the path of aromatic hydrocarbons painted on the skin of mice, and to see i f a simple means of detecting the metabolites was possible. Up to the present time, only one complete experiment and a few prelim-inary t r i a l s have been carried out. 1. Methods of "painting" mice and extracting tissue On two successive days eleven mice were painted with 0.2Dml. of a solution containing 0.75 grams of 1,2-benzanthra-cene in 100 mis. of benzene. Abscond group of mice were painted, with an equivalent amount of 9,10-dimethyl-l,2-benzanthracene. The benzene solution was applied dropwise to a clipped area of approximately 1.5 square centimeters on the lower dorsal surface of the mouse. One mouse from each group was sacrificed each day or every two days towards the end of the experiment. Weighed samples (0.10 to 0.30 grams) of the painted skin, the subcutaneous tissue below the painted area, and unpainted skin were extracted as follows. Each sample was placed in 3.0 mis. of water, heated just to boiling, and allowed to stand for forty-five minutes. The liq u i d was decanted and a second similar extraction was made. The combined extracts were evaporated just to dryness in an oven. Thr tissue was then placed i n 5.0 mis. of ether, heated to boiling - 93 -and allowed to stand for thir t y minutes. This was decanted, a second portion of ether was added, and the samples l e f t over-night. The following morning the samples were heated to boiling and the solution decanted. The combined ether extracts were also evaporated to dryness. To each of the residues was added 1.0 ml. of ether and 3.0 mis. of isopentane. The solution was then coiled to -180° and the fluorescence examined. The addition of one ml. of methyl cyclohexane saturated with naphthalene to the solvent gave a naphthalene suspension on coiling and consequenlty an energy transfer system of the type described in Results-, pages 32 to 46. 2. Results obtained Traces of the fluorescence from skin, subcutaneous tissue, and blood of an untreated mouse were taken. In both ether and water extracts there arises a broad, rather weak emission i n the region between 4800 to 5200 A. Fluorescence traces of the extracts of the treated mice were taken in the ether-isopentane solvent alone and in the solvent with naphtha-lene suspension. The graph in Figure 27 shows the intensity of the hydrocarbon emission per unit mass of tissue versus the number of days after the second painting. It was noted from work on systems of the pure hydrocarbons that both 1,2-benzanthracene and 9,10-dimethyl-1,2-benzanthracene solution systems show emission of the same intensity for identical amounts of material. Thus the 1,2-benzanthracene i s either more rapidly metabolized - 9 4 -id D w CO H u. 0 CO in I 3 o o h 2 D CC UI p-2 a o Z o I U J IO.O u. 0 r-W Z UI I-2 H FIGURE 27- Rate of disappearance of hydrocarbon painted on the skin of mice as measured by the inten-s i t y of fluorescence i n isopentar methyl cyclohexane solvent \ \ \ \ \ I O - D I ^ E T H Y L -U B E N Z R N T H R R C E N E L# I, 2 - B E N Z R N T H R R C E N E X N UMBER s O F DF»YS — * * — *» — - — r -» f i 7TlS.-<—r IO e-fiFTER S E C O N D P R I N T I N G 15" - 95 -or more effectively complexed to the tissue proteins than the more carcinogenic 9,10 dimethyl-derivative. During the f i r s t few days small amounts of hydrocarbon were detectable in water extracts of the skin and ether extracts of subcutaneous tissue. . , Although preliminary t r i a l s ^indicated that i t might be possible to follow the diffusion into the inner tissue, no evidence of such diffusion could be detected in the detailed experiment. The small amounts of hydrocarbon found on tbe unpainted skin areas of the mice result from a purely mechan-i c a l transfer. No fluorescing metabolites could be detected. However, these products may fluoresce in the region from 3100 to 3300 A. and thus they would be obscured by scattered Hg-arc radiation. No trace of hydrocarbons or of metabolism products could be founds in the blood. It should be noted in this respect that only a small percentage of the hydrocarbon i s converted to the phenolic derivatives (Appendix 4). The extraction of such compounds would also be more successful with, sodium hydroxide solution than with water. Checks on the reproducibility of our results were obtained by painting groups of six mice with 1,2-benzanthracene and sacrificing them at the same time. When the mice were sacri-ficed two days after the f i n a l painting, the hydrocarbon emission intensity varied from two to twelve of the arbitrary units shown on the graph in Figure 27. A uniform intensity of approximately two units was obtained when the mice were sacrificed on the sixth day. During the experiments i t was noted that the areas painted with the solutions of 1,2-benzanthracene appeared unaf-fected and the clipped hair grew back normally. The areas painted with 9,10-diaethyl-l,2-benzanthracene appeared very red and irr i t a t e d by the f i f t h day. The hair f e l l out, the blood vessels on the underside of the siiin seemed enlarged, and the skin was very bloody. After ten days the excessive bloodiness disappeared and the area became covered with tough scale-like scar tissue. Further work w i l l be done on the rates of disappearance of other carcinogenic and non-carcinogenic hydrocarbons. Other problems to be investigated include the effect of solvent or of the addition of a second hydrocarbon on the apparent rate of disappearance of hydrocarbon from tissue. 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Weigert, Cancer Res. 8_, 169 (1948) F.Weigert, G.Caleutt, and A.K.Powell, Brit.J.Cancer 1, 405 (1947) F.?feigert and J.C.Mottram, Cancer Res.. 6_, 97 (1946) F.Weigert and J.C.Mottram, Cancer Res. 6_, 109 (1946) H.Weil-Malherbe, Cancer Res. 4, 102 (1944) - 113 -APPENDIX 1.  PURIFICATION OF MATERIALS USED It i s obvious that high, purity of both solvents and solutes was essential since impurities might act as acceptors of energy absorbed by the major components. I. SOLVENTS USED PT MAKING GLASSES Most of the commercial solvents contained fluores-cent materials. Those solvents which were to be used i n low temperature glasses were f i r s t carefully dried. The ether was then d i s t i l l e d in a glass s t i l l i n the presence of iron wire and stored in a dark bottle with more iron wire to prevent peroxide formation. Isopentane was passed through a column of activated s i l i c a gel and d i s t i l l e d from the glass s t i l l . Methyl cyclohexane was treated repeatedly with port-146 ions of concentrated sulphuric acid, washed with, sodium bicar-bonate solution and with water, dried, and d i s t i l l e d . Methanol, ethanol. and isopropanol had to be redis-t i l l e d every five to seven days in order to remove the dimers or polymers which form continuously (8) and which shoxv a green phosphorescence. II. AROMATIC HYDRO CARBONS The commercial samples of polycyclic hydrocarbons a l l contained small amounts of other hydrocarbons which could be removed only by repeated chromatographic a d s o r p t i o n . 1 3 0 * 1 9 6 For chrysene and naphthacene the solvent used was a 1:4 mixture - 114 -of r e - d i s t i l l e d benzene-petroleum ether (boiling point 65-110°C.)» for the other hydrocarbons petroleum ether alone was used. The chromatograms were prepared i n glass tubes (40 x 3 cm.) with a stopcock at the lower end and a ground joint near the middle. A thick suspension of 100 mesh alumina (activated at 250°C. for twelve hours) in the solvent to be used, was poured into the tube which was already h a l f - f i l l e d with solvent. The alumina was allowed to settle and solvent was drawn through the column u n t i l i t appeared well-packed. One hundred to two hundred mgm. of hydrocarbon i n a minimum quantity of solvent were placed on the column and the chromatograph was developed with more solvent, The progress of the hydrocarbons was followed with ultra-violet l i g h t , irradiation times were kept to a mini-mum in order to reduce the possibility of hydrocarbon photoxid-ation. Tbe desired fraction was collected as i t passed from the column and the solvent was evaporated. Most impurities remained near the top of the column or descended more slowly than the desired hydrocarbon. Although a couple of chromatographs removed most of the impurity, eight or ten treatments were required to obtain almost pure material (e.g. anthracene free of napnthacene). The d i f f i c u l t y in removing the f i n a l traces of impurity hydrocarbons i s doubtlessly due to the formation of a complex of the type described in the body of the thesis. - 115 -APPENDIX 2. SYNTHESIS OF ANTHRACENE AND OP 2-METHYL ANTHRACENE It was seen found that anthracene from a l l commercial, sources showed i n i t s low temperature suspension emission the bands which were later attributed to naphthacene impurity. At f i r s t i t appeared possible that these bands might be anthracene i bands whose intensity was increased on the addition of naphtha-cene. However, in the anthracene whieh we carefully synthesized and purified, no trace of these bands was found. I.Synthesis of Anthracene 52 192 A. Preparation of o-benzoyl benzoic acid ' The prodedure used involved the coupling of phthalic anhydride and benzene in the presence of aluminun chloride to give o-benzoylbenzoic acid. This was dehydrated with concentrat-ed sulphuric acid to give anthraquinone which was then reduced. Fifteen grams of phthalic anhydride and seventy-five mis. of benzene were placed in a five hundred ml. round-bottomed flask equipped with a short condenser, the top of which was connected to an HCl trap. The flask and' i t s contents were coiled in an ice-bath and thirt y grams of anhydrous aluminum chloride was added. As soon as the action was proceeding smoothly, the mixture was shaken and refluxed on a steam-bath for one-half hour. The flask and i t s contents were cooled i n ice and the aluminum compound was decomposed by the careful addition of ice. Twenty mis. of concentrated hydrochloric acid and one hund-red mis. of water were added next. The excess benzene was removed - 116 -by steam d i s t i l l a t i o n , and the aqueous solution containing the aluminum chloride was decanted. The o i l y residue of benzoyl benzoic acid was washed with water. Traces of aluminum oxide or hydroxide were removed by dissolving the o i l y acid i n two hundred mis. of warm four percent sodium carbonate solution. The solution of the sodium salt of the acid was cooled in ice, stirred with one gram of activated charcoal, and f i l t e r e d . The o-benzoylbenzol& acid was precipitated as a monohydrate by the careful addition of HCl.. 52 76 192 B. Preparation of anthraquinone' ' ' The o-benzoylbenzoie aeid was heated with one hundred and twenty-five mis. of concentrated sulphuric acid at 100°C. The anthraquinitne formed was precipitated by pouring the hot solution onto five hundred grams of ice. After a short period of digestion, the preciputate was f i l t e r e d and washed with water and with dilute ammonia to remove traces of the starting mater-i a l s . The anthraquinone was recrystallized several times from glac i a l acetic acid. The f i n a l yield was 16.9 grams (81 % ) ; melting point - 285.5° corrected. n r, a 4.- » . 74,80,127,128,192, C. Reduction of anthraquinone to anthracene Twenty-five grams of zinc dust were allowed to stand for a few minutes i n an aqueous solution of 0.1. gm. of copper sulphate. The solution was decanted and to the activated metal were added four hundred mis. of 2 N sodium hydroxide, one hundred mis. of toluene, and ten grams of anthraquinone. The mixture was heated under reflux for seventy-six hours. The mixture was allowed to cool slightly. One hundred - 117 -mis. of benzene were added and the hydrocarbon layer was separ-ated from the zinc and the water layer. The hydrocarbon solution was concentrated to t h i r t y mis. and allowed to cool. Anthracene separated as colourless fluorescent plates (melting point 217°C); The yield was ninety percent. This anthracene was recrystallized twice from ethanol and then was chromatographed eight times. D. Other preparation methods. A high temperature treatment of anthraquinone with zinc chloride, sodium chloride, and zinc was also found to 35 produce anthracene. However, i t was f e l t that with a temperature of 280°C. there might be a large number of side reactions. Anthracene can also be prepared by heating a l i z a r i n with zinc d u s t . 7 3 ' 1 3 8 However, the preparation of pure anthra-quinone was f e l t to be simpler than the preparation of a l i z a r i n . 192 Other methods involve the use of halogen compounds 53 or a type of dione synthesis. II . PREPARATION Off 2-METHYL AMHRACENE 2-methyl anthracene was prepared by the basic reduct-ion of 2-methyl anthraquinone according to the method outlined for anthracene 0% Pages 116-117. The ninety-two percent yi e l d of f a i r l y pure material (melting-point 207°C.) was subjected to additional purification by chromatography. Attempts to prepare 1,4-dimethyl anthracene both by the basic reduction of the anthraquinone and by the preparation and subsequent reduction of the anthrone"^0 have f a i l e d . - 118 -APPENDIX 3. UNREPORTED TRIPLET LEVELS OF CERTAIN AROMATIC HYDROCARBONS In r i g i d media.many organic compounds containing multiple bonds, especially aromatic compounds, nave been found to possess a second emission band in addition to the usual 113-115 fluorescence band The second band-was-found-at longer-wave-lengths. In most cases i t had a lifetime of several seconds —6 —8 in contrast to the usual fluorescence lifetime of 10 to 10 second. 113 114 Lewis and Kasha ' interpreted these long-lived lower energy states as metastable t r i p l e t states of the molecule. Direct evidence for the t r i p l e t state was obtained by paramagnetic measurements which showed that each fluorescein molecule in the. t r i p l e t state possessed two unpaired electrons, a n d by a study of the effect of heavy atomic weight substituents on aromatic mole-97, 120 cules. ' Many polycyclic hydrocarhons and their derivations 113 120 121 show rather bright t r i p l e t emissions. The energies •"'»•••"" and l i f e t i m e s 4 3 ' 6 7 > 1 1 3 » 1 2 0 > 1 5 1 of the t r i p l e t s of a wide variety of aromatic molecules are recorded i n the literature. Adirovich 1 discussed t r i p l e t processes i n crystal 99 121 phosphors. More recent theories on the t r i p l e t state ' and theoretical calculations of the phosphorescence transitions of aromatic molecules 82., _155 may also be found. The addition compounds of aromatic nitro-compounds and many aromatic hydrocarbons have been found to show short-lived emission whichN i s very similar to that of the hydrocarbon t r i p l e t s . 1 5 2 - 119 -In Table 6 a r e g i V e n the previously unreported trip-l e t emissions of several hydrocarbons. The maxima of the resp-ective complexes with 1 ,3 ,5-trinitrobenzene are also given. TABLE 6 - Isopentane-methyl cyclochexane solvent at - 1 8 0 ° C . Hydroaarbon Triplet Emission in A-Emmission of trinitrobenzene complexes! in A-9,10-dimethyl-l,2-benzanthracene i 6450 ,7150 ,7900 6250 ,6800 ,7600 LO ethyl « « 6110 ,6590 ,7210 i L*-methyl n n 5890 ,6400 ,7040 5650 ,6150 ,6850 >! ft n tt 6010 ,6600 ,7220 5600 ,6100 ,6630 5' •? tt tt 5980 ,6570 ,7220 5700 ,6260 ,7000 t* " tt tt 6000 ,6580 ,7230 6850,7700 5 " tf tt 5 9 5 0 , 6 5 5 0 , 7 1 5 0 6000 ,6630 .7350 tt tt 5890 ,6530 ,7070 6450 ,7010 > « tt n 5990 ,6500 ,7100 6350 ,7200 > » tt it 6000 ,6560 ,7280 5550 ,6050 ,6550 ? • " n « 6030 ,6590 ,7200 6550 ,7170 ' j M tt . tt 5960 ,6480 ,7110 5860 ,6310 ,6550 3 « tt n 6150 ,6790 ,8800 5950 ,6430 ,7100 .0 M tt 'vi- 6130 ,6650 ,7500 7100 , >enzo(c)phenanthrene 5 0 4 0 , 5 4 2 0 ' 5150 ,5475 L methyl benzo( c)phenanthrene 5280 ,5630 I « tt ft 5060 ,5440 5230 ,5545 5 " tt tt 5060 ,5460 5280 ,5560 1 " w n 5070 ,5475 5370 ,5700 f D 2 n ft 5070 ,5476 5180 ,5520 3 V. « tt 5080 .5490 5260 ,5660 3,4,5,8,9,10-hexahydropyrene 5050 ,5100 naphthacene 5100 ,5550 ,6110 9 - 120 -APPENDIX 4 LIBERATORS SURVEY ON MODE OF ACTION OF CARCINOGENIC HYDROCARBONS During the last twenty years many research workers have devofled their time to various aspects of the cancer problem. A summary of their results would f i l l many volumes. Thus the survey given here w i l l include only work which attempts to elucidate the mode of reaction of carcinogenic hydrocarbons inside the body of an animal. I. ACTIVITY OE VARIOUS COMPOUNDS Dozens of polycyclic aromatic hydrocarbons, related substituted compounds, and photo-oxidation products have been synthesized and their carcinogenic ac t i v i t y determined by paint-ing them onto or by injecting them into mice, rats, and rabbits. 264,266,288,289,297,298,313 S j J a i l a r g t u d i e a ^ b e e n 280 3P7 out for polycyclic heterocyclic compounds. - '*"* Badger and Lewis have presented an account of the work on the chemical constitution and carcinogenic activity of certain azo-compounds. A comprehensive survey of a l l compounds, both inorganic and organic, which have been tested for carcinogenic activity has 303 been published by Hartwell. It has been found that even a change i n the position of a methyl group may significently alter the carcinogenic a c t i v i t y , 2 9 7 > 2 9 8 > 3 1 3 In evaluating the results one must remem-ber that various -animals and various tissues show different degrees of susceptibility to a given compound. 2 6 8 , 2 7 1' 3 1 9 II. METABOLISM OF COMPOUNDS  A. Methods employed - 121 -Quantitative studies of carcinogen metabolism have 270 342 *50Q led to the development of spectrographs and chemical 312 means of determining the amounts of hydrocarbon and related compounds in the tissues and excreta of treated animals. Detailed 270 methods for extracting the compounds have also been given. ' 342,347,349 B. Metabolic products and pathway The exact nature and relative amounts of the various metabAlic products have been shown to depend on the type of animal and the method by which the carcinogen was administered. Typical products were found to be 1,2,5,6-dibenzanthracene, 8- and 10-hydroxy-3,4-benzpyrene, and 3,4-benzpyrene-5,8- and 5,10- guinones. 2 6 9 > 2 7 2 > 284-287,295,310,311,316,331,348,350 1,2-dihydroxy-dihydro-naphthalene, -anthracene, or -phenanthrene and 9,10 dihydroxy-dihydro-phenanthrene have been identified as metabolic products of the respective non-carcinogenic hydrocar-267 bons in mice and rabbits. Carcinogenic hydrocarbons administered as food or injected intraperitoneal were largely excreted in the feces. Some was retained by the fore-stomach and a l i t t l e entered the b i l e . Hydrocarbons injected into the blood vessels quickly l e f t the blood. They and their derivatives were found i n the lungs, l i v e r , and adipose tissues. In some cases much of the hydrocarbon remained at the site of subcutaneous injection for periods up to two seeks. For several years, even the most carefully controlled experiments had been unable to account for a l l the hydrocarbon - 122 -which, was painted onto or injected into an animal. For example, when 1,2,5,6-dibenzanthracene i n olive o i l was injected subcut-aneously into rats, thirty-six percent of the hydrocarbon was found stored i n vesicles near the site of injection, four percent was found in the feces, and one percent was found as 4',8»-dihy-droxy-l,2,5,6-dibenzanthracene throughout the body and excreta. Recent work with hydrocarbons containing one or two 14 C atoms have shown that 5-hydroxy-l,2-naphthalic acid i s a 305 metabolite of 1,2,5,6-dibenzanthracene. Thus the polycyclic compounds appear to be broken down into simpler structures than was hitherto supposed. In these radioactive studies one hundred percent of the administered compound was accounted for. A quanti-tative measure of the hydrocarbon and of i t s various types of derivative was made in the different parts of the animal at definite t i m e s . 3 0 4 The studies with radioactive carcinogens also showed that even after prolonged extraction and saponification, some hydrocarbon derivative remained in the tissue residue. Conjugated proteins containing the 1,2-benzanthryl radical as the prosthetic group had already been prepared from the hydrocarbon isocyanates, 293 320 Just recently M i l l e r has found that the epidermis of li v i n g mice treated with benzene solutions of 3,4-benzpyrene contains fluorescent substances chemically bound to the protein fraction and apparently derived from the carcinogen. Alkaline hydrolysis of the protein irj. the presence of zinc dust released a neutral and an acidic compound. The epidermis of mice exposed to sunlight contained only forty percent as much fluorescent - 123 -material as the epidermis of mice kept in darkness. C. Effects on tissue Aromatic hydrocarbons painted on the skin appeared to damage the intracellular structure of the dermal mast ce l l s . 343 The rate of destruction of the sebaceous glands seemed to parallel the degree of activity found oh applying solutions of 283 different hydrocarbons to the skin of different animals. The rate of disappearance of hydrocarbon from the mouse following various modes of application and injection parallel the carcino-271 genie ac t i v i t y . The application of hydrocarbons to mouse skin was found to alter the c e l l permeability. Methyl cholanthrene on the f i r s t application entered the sebaceous glands, subcutaneous fat and l i p i d s ; while on successive applications i t went into 339 the c e l l cytoplasm. Successive applications of several different hydro-carbons were found to exert an additive carcinogenic effect, and thus an attempt was made to determine i f carcinogenesis was 317 an accumulation of abnormal protein within a c e l l . E v i d e n c e for the development of latent tumor cells was provided by Beren-274 blum and Shubik who found that croton o i l applied forty-three weeks after a single painting of the skin with 9,10-dimethy1-1,2-benzanthracene produced a tumor incidence similar to that occurring when the interval was three weeks or less. By i t s e l f croten o i l has no apparent carcinogenic activity. D. Studies of human cancer - 124 -Human tumor tissue and excreta from cancer patients have been studied extensively in an attempt to determine the 262,296,830 difference from their normal counterparts. In a few cases significant differences have been found, but in general no data capable of explaining the basic mechanism of carcino-genesis has been tbtained. A group of leukemia patients who were given intravenous injections of 3,4-benzpyrene showed a temporary decrease in the amount of protein i n the plasma. A phenolic metabolite was also 308 produced. III. 1ACT0BS WHICH mEMSMCB THE POTENCY OF CARCINOGENIC HYDROCARBONS A. Solvent effects A change of solvent may significantly alter the average induction period of tumor p r o d u c t i o n . 2 9 0 ' 2 9 4 ' 3 2 9 ' 3 4 1 For example, the addition of liq u i d paraffin to.ether or benzene solutions of 3,4-benzpyrene, and the use of acetone in place of benzene as a solvent for methyl-cholanthrene shortened the resp-ective induction periods by several weeks. At f i r s t i t was believed that methyl-cholanthrene 337 dissolved in anhydrous lanolin had no carcinogenic properties. Later work has shown that the carcinogenic properties reappear when the methyl-cholanthrene concentration becomes high, and i t was concluded that the "solvent effect" wasattributable to the effective concentration of hydrocarbon in the sebum of the skin. 273rreatment with "inactive" methyl-cholanthrene (dissolved in lanolin) greatly increased the sensitivity of the skin to a sub-sequent application of the "active"carcinogen (dissolved in - 125 -benzene. B. Radiation effects Mice painted with carcinogenic hydrocarbons developed fewer skin carcinomas when they were exposed to ultra-violet or visible light than when they were kept i n darkness. However, the development of leukemia seemed to be stimulated by this same r a d i a t i o n . 2 9 9 ' 3 2 3 C. Mixtures of hydrocarbons The addition of a non-carcinogenic or slightly car-cinogenic hydrocarbon to a solution of a carcinogen has i n sev-eral cases been found to prolong the mean latent period and to reduce the yield of induced t u m o r s . 2 8 1 ' 3 0 7 ' 3 1 4 ' 3 1 5 , 3 3 4 ' 3 4 0 ' 3 4 5 The activity of 9,10-dimethyl-l,2-benzanthracene i s reduced by 6,8-dimethyl-l,2-benzanthracene or by 1,2,5,6-dibenzoIluorene; that of methyl-cholanthrene by 1,2,5,6-dibenzofluorene; and that of 1,2,5,6-dibenzanthracene by 1,2,5,6-dibenzacridine. D. Addition of sulphur compounds The activity of hydrocarbons was also reduced byx the simultaneous application of 2,3-dimercapto-propanol. Momothiol 292 compounds were without effect on the carcinogenic activity. iy.SBSClAL REACTIONS OF HYDROCARBONS Another approach to the problem of carcinogenesis ' has been made through a study of certain reactions which involve carcinogens and which may be important in biological systems. The ultra-violet irradiation of 3,4-benzpyrene pro-- 126 -duced two substances capable of inhibiting urease activity. As one of these was hydrogen peroxide i t was concluded that 3,4-benzpyrene can act as a photosensitizing catalyst in the product-325 ion of hydrogen peroxide during ultra-violet irradiation. That the second inhibitory effect was due to the action of benz-pyrene on the urease sulfhydryl groups was shown by the a b i l i t y of cysteine to prevent the urease inactivation and by the treat-322 ment of urease samples with p-chloro-mercuribenzuate. Gutmann and Wood w presented evidence for the lack of formation of a mercapturie acid as a result of conjugation of cysteine and benzpyrene. The oxidation of 3,4-benzpyrene i n the presence of autoxidizing thiols was found to be. due to the formation of hydrogen peroxide. Aromatic hydricarbohs have been found to be oxidized in the dark by ascorbic acid through the action of the enediol group of the acid molecule. 3 4 4 A coupled oxidation was found to account for the apparent disappearance of carcinogenic hydrocar-bons placed in autoxidizing fatty a c i d s . 3 2 4 > 3 2 s The ac t i v i t y of 3,4-benzpyrene and of 1,2,5,6-dibenz-anthracene was found to be decreased by maleic and citraconic anhydrides, but not by malonic acid or other lower aliphatic aldehydes. It was also shown that the unsaturated fiompounds would combine with -SH groups. 2 9 1 Some agreement was found bet-ween carcinogenic activity and the a b i l i t y of the hydrocarbon to act as a catalyst on autoxidizing systems by increasing or de-creasing the rate of oxidation. For example, the autoxidation of - 127 -benzaldehyde was inhibited by a mixture of hydrocarbons and carotene in a solvent containing carbon tetrachloride. Benzoyl peroxide became oxidized i n the presence of one of a group of aromatic hydrocarbons. 3 1 9' 3 4 6 7. THEORIES PROPOSED TO ACCOUNT FOR THE CARCINOGENICITY OF  CERTAIN AROMATIC HYDROCARBONS It has been pointed out that carcinogenic activity i s not an " a l l or nothing" property of hydrocarbons. Recently Steiner and F a l k 3 4 0 have shown that the subcutaneous injection of 5.0 mgm. of the supposedly inactive chrysene or 1,2-benzanth-racene has the same effect as the injection of 0.02 mgm. of 1,2, 5,6-dibenzanthracene or 2©-methyl-cholanthrene. Ho relation has been found between absorption and emission band position or intensity and carcinogenic activity. 278,306,321,336,351 Carcinogenic and non-carcinogenic hydrocarbons have been found to have similar chemical reactivities anfi similar rates of photoxidation. 2 8 9 A mechanism of carcinogenic action involving a reaction with protein sulphur groups was proposed by Buu-Hoi. 2 7 9 The f i r s t attempt to find a relationship between the carcinogenic activity and electronic structure of aromatic hydro-carbons was made by Schmidt^ U , J who suggested that the IT-electrons were the origin of the activity. He regarded aromatic hydrocar-bons as made up of benzene and naphthalenic groups, between which were groups of two carbon atoms whose electrons were responsible for the activity. However, the agreement of this theory with experimental results was rather poor. - 128 -27 ^ Bergmann f e l t that a carcinogen in a l i v i n g c e l l was aasorbed by an acceptor possessing a definite surface area. Carcinogens possessed a limiting size and could be inactivated by substituents which prevented proper adsorption. In 1944 Fieser 3 0 0 advanced a theory of carcinogenesis which involved a select-ive adsorption of the carcinogen to the c e l l wall so that the c e l l permeability was affected. Metabolic attack was assumed to occur at the exposed surfaces rather than at the active centers, and thus the particular phenolic derivatives which had been found could be accounted for The charge on the K>region (the bond corresponding to the 9,10-phenanthrene bond) has been calculated for a large number of substituted polycyclic hydrocarbons and heterocyclics 332 333 by the "method of molecular diagrams". ' In a large number of cases excellent agreement is found between the physiological activity and the magnitude of the charge. However this theory does not explain the inactivity of compounds of 1,2-benzanth- ' racene with substituents on the angular ring, or the very slight activity of acenaphthanthracene. The rate of addition of osmium tetroxide to the K-region was found to give a better correlation than the values 263 calculated by A. and B. Pullman. Bond orders calculated by the molecular orbital method gave better agreement with the osmium tetroxide data. Carcinogenesis was f e l t to involve forces similar to those in the derivatives of aromatic hydrocarbons and nitro compounds. 276 Boyland discussed carcinogenesis i n terms of a planar molecule endowed with two carcinogenophores (groups - 129 -endowed with special chemical reactivity) which may be activated by auxocarcinogenie groups. The sel f - p o l a r i z a b i l i t i e s at a l l positions of the 1,2, -benzanthraeene molecule have been calculated and related to the 301 act i v i t y of the different mono-methyl derivatives. In many hydrocarbon molecules there i s a correlation between the biological activity and the difference between the calculated and magnetically measured electronic derealizations. 328 The most recent theory of carcinogenic action invol-ves the po s s i b i l i t y of reaction or complex formation between 261 277 the active molecule and the nucleoproteins. > " Boyland has shown how a l l carcinogens, (physical,inorganic,, and organic) can react i n some manner with desoxyribonucleic acid. Complex formation was the mode-of reaction attributed to polycyclic hydrocarbons. Thus, i n spite of the large body of knowledge that has been gathered!, the exact effect of carcinogenic hydrocarbons on l i v i n g organisms at present remains unknown. - 130 -APPENDIX 5 LITERATURE SURVEY ON ABSORPTION AND EMISSION SPECTRA; PHOTO CHEMICAL REACTIONS, COMPLEX FORMATION, AND ENERGY TRANSFER  IN SYSTEMS CONTAINIHG CHLOROPHYLL AND CLOSELY RELATED  COMPOUNDS. . . . I. SPECTRAL PROPERTIES OF CHLOROPHYLL A. Hhloroplast pigments A l l photosynthesizing plants and baeteria contain one or more of the ten known chlorophylls, which are green tetra-pyrrolic magnesic compounds. The chloroplasts may also contain one or more of the phycoblins and carotenoids. Phyeoblins are blue or red proteinaceous pigments which are insoluble i n organic solvents. Carotenoids include the yellow, orange, and red carotenes (polyene hydrocarbons) and xanthophylls (oxygen derivatives of 213 polyene hydrocarbons). B. Absorption, fluorescence, and phosphorescence bands The absorption and emission spectra of chlorophyll 203,207,209,213,236,237,239,240,259(infra_red b a u d s 226 } > o f related compounds such as magnesium phthalocyanin, magnesium p o r p h y r i n , 2 0 8 > 1 9 8 > 2 1 8 > 2 2 4 and alkyl chlorophyllides 2 2 4, and of the other chloroplast pigments 2 1 5 ' 2 5 8 have been studied exten-sively. A rather weak phosphorescence with a lifetime of one-fifth of a second has been found to begin from 7800 to 8000 A. and to extend into the infra-red. , x o C. Effect of solvent For chlorophyll, changes of solvent were found to affect the positions and relative intensities of both the absor-ption and emission b a n d s . 2 0 7 ' 2 1 3 , 2 2 2 , 2 2 5 , 2 5 9 Chlorophyll - 131 -dissolved in dry hydrocarbon solvents showed a fluorescence yield of percent; while that dissolved i n ethyl ether, acetone, methanol, ethanol, or a hydrocarbon containing a l i t t l e water showed a fluorescence yield of ten percent. This change was not due to solvent polarity, and the temperature coefficient indicated that dimerization in the dry hydrocarbons was u n l i k e l y . 2 1 1 * 2 1 3 Thus the ten percent yield was considered to be characteristic of solvated chlorophyll molecules which might involve hydrogen bonds. 2 3 3 D. Effect of temperature The spectral changes which occur with a change of 216 225 242 259 temperature were also recorded. ' ' Increased temperatures were found to decrease the fluorescence intansity and to shift the banidumaxima to lov/er wavelengths. E. Effect of state of aggregation In l i v i n g leaves and in isolated chloroplasts a fluorescence yield of only 0.005 to 0.15 percent was obtained. x A continuous shift to lower energies of both the fluorescence and absorption bands was observed i n passing from chlorophyll suspensions to a r t i f i c i a l l y prepared colloids to l i v i n g l e a v e s . 1 9 7 > 2 0 9 > 2 1 3 > 2 3 9 - 2 4 1 This and other evidence which w i l l be presented shortly, indicate that i n l i v i n g leaves there i s a type of complex between chlorophyll and the chloroplast protein. An energy-level diagram for chlorophyll has also been worked out, and i t appears that there may be one or more inter-nal conversions of energy before fluorescence occurs. 2 1 3 The - 132 -possibility of a relationship between the efficiency of photo-synthesis and the amount of chlorophyll fluorescence at different 25*5 exciting wave-lengths of radiation has been investigated. P. Photo-bleaching phenomena Chlorophyll solutions, in the absence of oxygen, i-jere often found to suffer a reversible photobleaching as a result of prolonged illumination with intense ultra-violet or visible light. 2 1 3» 2 3 5» 2 5 9 The reaction was reversed on removal of the light and the extent of the reaction paralleled the photo-chemical properties under similar conditions. That the rever-sible photobleaching occurred at -180°C. in rigid solvents indicated that it was not due to bimolecular transmutations, but that i t might arise from electron or proton transfer to the solvent. 2 2 9 The presence of minute traces of oxygen seemed to eliminate the reversible aspect of the photo-bleaching. II. ENACTIONS OP CHLOROPHYLL A. Chlorophyll as a sensitizer In some cases chlorophyll has been found to photo-sensitize oxidation-reduction reactions with a yield approaching one. Such reactions may occur with oxygen and with oxidizing 213 agents such as azo dyes. However, chlorophyll sensitized oxidants are specific in that they occur only i f certain reducing agents are present. For example, chlorophyll has been found to photo-231 catalyse the oxidation of phenylhydrazine by methyl red or o-dinitro-benzene and the oxidation of ascorbic acid with - 133 -o-dinitro-benzene. 2 2 0PyTuvic acid was found to take up carbon dioxide i n the presence of an irradiated chloroplast preparation 234 with certain enzymes also included. Chlorophyll was also 1 238 240 found to be capable of sensitizing photographic plates. ^°>* w A short refrigeration i n paraffin o i l at -13°C. or a freezing of longer duration i n liq u i d a i r was found to destroy 221 the a b i l i t y of plant cells to reduce silve r nitrate. Many of these reactions appeared to involve a transfer 238 of energy. It was also noted that the photo-chemically active state was not the directly excited singlet state, but an indir-213 231 ectly formed long-lived state. ' B. Quenching in systems containing chlorophyll As with many hydrocarbon systems, the fluorescence of chlorophyll was quenched, or suffered an intensity decrease^. when the concentration of the solution became high or when certain compounds were added to the solution. Fluorescence quenching was shown for solutions of a chlorophyll/and solutions of chlorophyll b when the concent--3 ration exceeded 2 x 10 moles per l i r e r . The temperature coef-f i c i e n t indicated that self-quenching resulted from a resonance exchange of energy (to be discussed more f u l l y later), rather than from a formation of non-fluorescent dimers or from 257 collisions of the second kind. ' At concentrations of 2 x IO" 4 moles per l i t e r , chloro-phyll b was found to sensitize the fluorescence, of chlorophyll a. This quenching of chlorophyll b by chlorophyll a was more efficient than either the self-quenching of chlorophyll a or -134 -that of chlorophyll b . 2 5 7 Anbxtensive search for compounds which quench and compounds which do not quench chlorophyll fluorescence has a 206,207,230,232 been made, Quenchers included many oxidizing agents and certain amino aromatic reducing agents. L i t t l e change in the chlorophyll absorption spectrum was observed with oxygen, quinone, or hydroquinone quenchers, while iodine and dinitro-benzene decreased the intensity of the absorption bands. There was some correlation between a compound's a b i l i t y to quench chlorophyll fluorescence and i t s a b i l i t y to inhibit 230 polymerization reactions. Other workers f e l t that oxygen might shorten the duration of the excited state of chlorophyll., 206 Photo-reactions xvere found to occur with osygen and with the non-quencheri. ascorbic acid, but no reaction occurred with the quenchers, quinone and hydroquinone. This absence of a r e l -ation between quenching and photo-reaction indicated that the latter might be determined by the long-lived t r i p l e t state of chlorophyll and the former by the excited singlet state with a -8 206 life-time of 10 seconds. Later work showed that quenching required the presence of both water and oxygen. Dry oxygen had no quenching effect, and i t has already b.een noted that water alone gives an increase 206 to the fluorescence intensity of chlorophyll. Magnesium phthalocyanine adsorbed on magnesium oxide showed increased flourescence in the presence of a l i t t l e oxygen and decreased fluorescence when the oxygen concentration was increased. It was f e l t that in the former case the osygen was adsorbed onto the magnesium, while in the latter case i t was - 135 -attached to the peripheral atoms. 2 1 9 C. Chlorophyll complexes On Page 131 i t was pointed out that changes i n the absorption and emission bands indicated that in a chloroplast the chlorophyll might be bound to the protein material. Solvent extractions have presented further evidence for a ehlorophyll-. „ H . j. . , , 200,213,228,238,240,241 protein link, and for a lipoid-protem link. Chlorophyll i n l i v i n g cells i s much less reactive than that in solution. The electrophoretic properties and isoelectric points of several a r t i c i c i a l l y prepared chlorophyll-protein complexes 210 have also been studied. Complexes have been found to form between chlorophyll art certain inorganic ions, such as those of copper and z i n c . 2 0 1 -' Some workers have f e l t that the quenching of fluorescence discussed on the previous page may be explained by complex formation. ' Additional support for this idea i s provided by the observation that minute traces of oxygen were able to 213 235 259 prevent reversible photo-bleaching. ' » Chlorophyll could be protected from oxidation by a i r or by hydrogen peroxide and f e r r i c hydroxide by mean3 of com-pounds such as nitrobenzene, nitro-naphthalene, or p-nitro-toluene which appeared to form complexes stoichiometrically. The addition of phenol, hydroquinone, or resorcinol to chloroC phyll in the ratio of one to two hundred and f i f t y chlorophyll 244 molecules similarly prevented the oxidation. It was supposed that this l a t t e r group of compounds complexed with the excited - 136 -chlorophyll molecules. 256 Recent work has suggested that chlorophyll and phenylhydrazine in the dark at room temperature in polar sol-vents form a molecular compound with binding insufficient to affect the absorption of the former, but sufficient to quench i t s fluorescence. The simultaneous activation and quenching of chlorophyll fluorescence i n non-polar solvents indicated two modes of addition. III. ENERGY TRANSFER PHENOMENA IN CBIX3R0PHYLL SYSTEMS The application of mathematics to describe the process 212 6f photosynthesis and the discussion of the possibility of energy transfer in li v i n g chloroplasts have long been subjects 54-57 of special interest to theoreticions. Forster has predicted a transfer of energy between chlorophyll molecules in solution over a distance of 80 A. It has been mentioned that at coneen--4 trations of 2 x 10 moles per l i t e r chlorophyll b can sensitize the fluorescence of chlorophyll a. This i s in rather good agree--4 ment with the concentration of 8 x 10 moles per l i t e r at which 257 Forster preducted such a transfer should occur. If energy transfer i s sloxv compared to vibrational deactivation the system should behave as a group of individual molecules, while i f the exchange is fast there i s a giant macro-molecule. 199,214 su^k systems, excitation energy absorbed at 213 9PA one spot might be u t i l i z e d at another. Some workers have shown evidence for the existence of a photosynthetic unit composed of several hundred chlorophyll molecules. There ±s also evidence for a long-lived intermediate state of chlorophyll which - 137 -204 238 257 plays an important role i n photosynthesis, ' ' The most definite example of energy transfer i n chlorophyll systems is that which occurs between chlorophyll and the other chloroplast pigments. The efficiency of photosynthesis has been found to be high in regions where i t appears, from studies of extracted pigments, that chlorophyll does not absorb. Thus i t has been postulated that energy absorbed by the carote enoids and by the phycoblins may be transferred to the chloro-205 213 phyll which can perform such steps as hydrogen transfer. ' ' 217 223 243 ' ' No energy transfer from carotenoids to chlorophyll has been found to occur in acetone s o l u t i o n s 2 0 5 so i t appears that such transfer requires the components to be either adsorbed or colloidal, 17. POSSIBLE PHOTOSYNTHESIS MECHANISMS. On the basis of the work described here and the work in other f i e l d s , several mechanisms for photosynthesis have been proposed. However, only $wo of the most plausible w i l l be noted. The f i r s t suggested that hydrogen donor supplied to the cells externally was converted by enzymatic dark processes to an energy acceptor which contacted a chlorophyll molecule. Light absorbed by the chlorophyll was transferred to the energy acceptor. This energized acceptor then reacted at another dark catalytic surface with carbon dioxide or a derived product. 2 1 3 In the second mechanism there was photochemical oxidation of water by an intermediate oxidant followed by an enzymatic liberation of molecular oxygen. Barbon dioxide was - 138 -enzymatically fixed and reduced by the product of the f i r s t 199 260 step. ' It was hoped that more information might ,)be obtained through a study of photo-catalysts such as FeCl^ i n the reduc-tion of thionine by alcohol. Thus, i t appears that a knowledge of energy transfer and complex formation in simpler systems might enable one to . further elucidate the mechanisms of photosynthesis. 

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