Donor-acceptor systems have unique properties that make them ideal candidates for solar energy harvesting through mimicry of natural photosynthesis. This dissertation is focused on unraveling those unique properties in various types of donor-acceptor systems. The systems investigated are categorized as closely linked, push-pull, supramolecular, and multi-unit. As part of the study, photosynthetic analogues based on BF2-chelated dipyrromethene (BODIPY), porphyrin, phthalocyanine, truxene, ferrocene, quinone, phenothiazine (PTZ), perylenediimide (PDI), fullerene (C60), dicyanoquinodimethane (DCNQ), tetracyanobutadiene (TCBD), and triphenylamine (TPA) are investigated. The effects of proximity between donor-acceptor entities, their geometrical orientation relative to each other, push-pull character of substituents, and competitive energy and electron transfer are examined. In all systems, primary events of photosynthesis are observed, that is absorption and energy transfer and/or electron transfer is witnessed. Ultrafast transient absorption spectroscopy is utilized to characterize the photo-induced events, while other methods such as steady-state luminescence, cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and computational calculations are used to aid in the characterization of the donor-acceptor systems, in particular their applicability as solar energy harvesters.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第25311号 / 工博第5270号 / 新制||工||2002(附属図書館) / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 杉野目 道紀, 教授 中尾 佳亮, 教授 石田 直樹 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

The vapor phase photochemistry of the three isomeric cyanopyridines and the three methylpyridines was studied by irradiating their vapors at 254 nm. It was found that direct irradiation of any one cyanopyridine isomer resulted in the formation of the other two isomers of cyanopyridine or methylpyridines respectively. The reactivity of each isomer was found to be different. This was suggested to be based on the stability of their azaprefulvene intermediates formed during interconversion. The phototransposition of these molecules was suggested to result from 2,6-bonding, nitrogen migration around the five sides of cyclopentenyl ring followed by rearomatization. This mechanism was found to be consistent with the results of deuterium labeling studies of cyanopyridines These result suggest that cyanopyridines undergo phototransposition via the intermediacy of azaprefulvenes instead of Dewar-pyridine and azaprismane. Thus, photochemical studies showed that the six trideuteriopyridine isomers constitute two separate photochemical triads. Each triad consists of three isomers that are photointerconverting upon irradiation at 254 nm in the vapor phase. Similary, it was found that the three isomeric tetradeuteriopyridine isomers also constitute a photochemical triad and are interconverting upon irradiation at 254 nm in the vapor phase. These phototranspositions are best explained by the cyclization, nitrogen migration, and rearomatization mechanism. These results are in contrast to the long-held belief that pyridine is photostable in the vapor phase. Instead, unlabeled pyridine undergoes a hidden phototransposition leading back to itself.

A series of 2,5-diarylidene-cyclopentanones (ndbcp), their protonated cations (ndbcp-H+), and a substituted compound, 2,5-bis-[3-(4-dimethylamino-phenyl)-allylidene-cyclopentanone (2dbma) have been synthesized. Their electronic absorption and fluorescence spectra have been measured. The absorption spectra have been assigned with the aid of INDO/S calculations. Molecular structures used for the INDO/S calculations were computed with the PM3 Hamiltonian. Polarized excitation spectra have been measured for 2dbcp and 3dbcp at 77 K in ethanol/methanol glass and used as an aid for the assignments of electronic transitions. Absorption and fluorescence spectra have been measured in solvents of varying polarity for all compounds synthesized. The influence of hydrogen bonding on the excitation spectra of compounds has been investigated. Solvent induced shifts in the absorption and fluorescence spectra of 3dbcp and 2dbma in combination with the PM3 calculated ground state dipole moment have been used to determine the excited state dipole moment of these compounds. Fluorescence quantum yields have been obtained to analyze the changes in the nonradiative rate of decay from S1. The protonated cations have been prepared in acids of different strength. The influence of acid strength on the excitation and emission spectra has been analyzed by gradually diluting acid solution. Evidence for excited state proton transfer in weak acids has been obtained for 2dbcp and 3dbcp. Brief photochemical studies of 1dbcp and 1dbcp-H+ have been carried out and analyzed by HPLC.

Os compostos carbonílicos no estado triplete (CCT) são considerados espécies reativas de oxigênio uma vez que possuem comportamento químico semelhante ao de radicais alcoxil. Quando formadas em sistemas biológicos, estas espécies podem estar envolvidas tanto em processos benéficos quanto deletérios ao organismo, como é o caso da lipoperoxidação, onde CCT não só são gerados como também iniciam ou amplificam o processo. Visando estudar a capacidade de dienos conjugados de suprimir a energia triplete de tais compostos, de forma a diminuir seus efeitos deletérios, determinou-se as constantes de supressão, para quatro diferentes dienos, de acetona triplete gerada pela da termólise do tetrametil-1 ,2- dioxetano e pelo sistema enzimático isobutanal/ \"horseradish peroxidase\"/O2 Todos os dienos apresentaram constantes de supressão de ordem difusional. Foi analisada também a forma pela qual os dienos suprimem a acetona triplete e concluiu-se que tanto dienos com hidrogênios alílicos (2,4-hexadienoato e seu éster etílico), potencialmente abstraíveis, quanto dienos sem estes hidrogênios (2 ,4-pentadienoato e seu éster metílico), suprimem a acetona por um processo físico de transferência de energia, que leva à sua fotoisomerização cis,trans. A reatividade destes dienos frente a espécies reativas de oxigênio comumente formadas em sistemas de lipoperoxidação, como o oxigênio singlete, radicais hidroxil, peroxil e superóxido, foi também testada, mostrando que nenhum dos dienos apresenta atividade sequestradora destas espécies. Experimentos preliminares de lipoperoxidação em sistemas biomiméticos (mitocôndrias e microssomos isolados de fígado de rato), mostraram que o trans, trans-2,4-hexadienoato de etila é capaz de inibir o inchamento mitocondrial induzido por benzofenona triplete e de suprimir a quimiluminescência de microssomos induzida por Fe2+/ ascorbato. Concluiu-se assim que dienos conjugados, contendo ou não hidrogênios alílicos, podem ser usados como supressores específicos de compostos carbonílicos triplete em sistemas biológicos e contribuir para o esclarecimento dos mecanismos de reação destes processos. / Triplet carbonyls can be named reactive oxygen species once they behave chemically as alkyloxyl radicals and therefore can potentially drive beneficial and deleterious processes in biological systems. In the case of lipid peroxidation, these species have been found not only to be reaction products but also to amplify the radical chain by hydrogen abstraction of polyunsatured lipid molecules. With the aim of finding efficient and reliable chemical probes for triplet carbonyls, we studied here the quenching properties of conjugated dienes, namely 2,4-hexadienoate and 2,4- pentadienoate anions and corresponding alkyl esters, upon triplet acetone generated either chemically (thermolysis of tetramethyl-1 ,2-dioxetane) or enzymically (aerobic oxidation of isobutanal/horseradish peroxidase). As expected, the quenching rate constants were found to be diffusion controlled, although those for the pentadienoate derivatives were 3-fold lower than those measured for the hexadienoates. Therefore, independently of the presence of allylic hydrogens in the diene probe, the triplet acetone quenching occurred by a physical process followed by cis,trans-isomerization, without hydrogen abstraction from the quencher. The reactivity of the studied dienes towards oxygen reactive species known to be formed during lipid peroxidation, such as singlet oxygen, and peroxyl, hydroxyl and superoxide radicals, was also investigated to assure they would not interfere with the radical lipoperoxidation chain. Indeed, none of the dienes showed antioxidant activity on classical model systems. Preliminary experiments with model systems widely used to study lipid peroxidation showed that the trans, trans-ethyl sorbate can inhibit the mitochondrial swelling induced by enzymically formed triplet benzophenone and to quench the chemiluminescence of microsome preparations challenged with iron/ascorbate. This is in agreement with reported work showing that the lipid peroxidation chain associated with mitochondria permeabilization and polyunsaturated fatty acid peroxidation is amplified by intermediate triplet carbonyl products. Altogether our data indicate that conjugated dienes can be used as specific quenchers of triplet carbonyls formed in biological systems without reacting with other reactive intermediates.

Oxidation of organic species, in particular dicarboxylic and humic acids, was investigated in ice. Products were analyzed by Proton Transfer Reaction Mass Spectrometry, ion and gas chromatography, and a Total Organic Carbon analyzer. Photolysis of succinic acid with H2O2, an OH precursor, produced malonic acid and malic acid, illustrating that diacids are subject to photochemical degradation in ice. First-order decay rate constants were an order of magnitude higher at room temperature (~23 °C) than in ice (-20 °C). A smaller difference was observed for malonic acid, a more soluble diacid, suggesting that partial segregation of H2O2 and succinic acid during freezing played an important role in the kinetics. VOCs, likely to be aldehydes and ketones, were produced from ice containing humic acid through heterogeneous ozonolysis and photooxidation which was enhanced by NO3-, an OH precursor. VOCs also formed from ice made from deionized water, likely through oxidation of organic contaminants.

Oxidation of organic species, in particular dicarboxylic and humic acids, was investigated in ice. Products were analyzed by Proton Transfer Reaction Mass Spectrometry, ion and gas chromatography, and a Total Organic Carbon analyzer. Photolysis of succinic acid with H2O2, an OH precursor, produced malonic acid and malic acid, illustrating that diacids are subject to photochemical degradation in ice. First-order decay rate constants were an order of magnitude higher at room temperature (~23 °C) than in ice (-20 °C). A smaller difference was observed for malonic acid, a more soluble diacid, suggesting that partial segregation of H2O2 and succinic acid during freezing played an important role in the kinetics. VOCs, likely to be aldehydes and ketones, were produced from ice containing humic acid through heterogeneous ozonolysis and photooxidation which was enhanced by NO3-, an OH precursor. VOCs also formed from ice made from deionized water, likely through oxidation of organic contaminants.

The aim of the investigation described in this work is to gain a better understanding of the processes involved in the oxidation of organic compounds by photolytic ozonation in a laboratory scale reactor. The results and discussions are presented in Chapter III. This chapter contains four parts. In the first part, mass transfer efficiency and the calculation of the mass transfer coefficient, KLa, as well as the ozone decomposition rate constant, KD, are presented and compared with those obtained by other investigators. The second part deals with the kinetics of the photolysis of 2,2',4,4',6,6'-hexachlorobiphenyl both in purified and natural lake water. Mathematical expressions and a discussion of the possible reaction processes involved are given. Kinetic models of ozonation and photolytic ozonation in purified and natural lake water are developed and discussed in part three. Rate constants are calculated from experimental data and used to predict values of substrate destruction with a mathematical model. The fourth part of this chapter deals with the identification of products from the photolysis, ozonation and photolytic ozonation of 2,2'4,4',6,6'-hexachlorobiphenyl. The products are isolated and identified using combined gas chromatography and mass spectroscopy, and reaction mechanisms are suggested.

Os compostos carbonílicos no estado triplete (CCT) são considerados espécies reativas de oxigênio uma vez que possuem comportamento químico semelhante ao de radicais alcoxil. Quando formadas em sistemas biológicos, estas espécies podem estar envolvidas tanto em processos benéficos quanto deletérios ao organismo, como é o caso da lipoperoxidação, onde CCT não só são gerados como também iniciam ou amplificam o processo. Visando estudar a capacidade de dienos conjugados de suprimir a energia triplete de tais compostos, de forma a diminuir seus efeitos deletérios, determinou-se as constantes de supressão, para quatro diferentes dienos, de acetona triplete gerada pela da termólise do tetrametil-1 ,2- dioxetano e pelo sistema enzimático isobutanal/ \"horseradish peroxidase\"/O2 Todos os dienos apresentaram constantes de supressão de ordem difusional. Foi analisada também a forma pela qual os dienos suprimem a acetona triplete e concluiu-se que tanto dienos com hidrogênios alílicos (2,4-hexadienoato e seu éster etílico), potencialmente abstraíveis, quanto dienos sem estes hidrogênios (2 ,4-pentadienoato e seu éster metílico), suprimem a acetona por um processo físico de transferência de energia, que leva à sua fotoisomerização cis,trans. A reatividade destes dienos frente a espécies reativas de oxigênio comumente formadas em sistemas de lipoperoxidação, como o oxigênio singlete, radicais hidroxil, peroxil e superóxido, foi também testada, mostrando que nenhum dos dienos apresenta atividade sequestradora destas espécies. Experimentos preliminares de lipoperoxidação em sistemas biomiméticos (mitocôndrias e microssomos isolados de fígado de rato), mostraram que o trans, trans-2,4-hexadienoato de etila é capaz de inibir o inchamento mitocondrial induzido por benzofenona triplete e de suprimir a quimiluminescência de microssomos induzida por Fe2+/ ascorbato. Concluiu-se assim que dienos conjugados, contendo ou não hidrogênios alílicos, podem ser usados como supressores específicos de compostos carbonílicos triplete em sistemas biológicos e contribuir para o esclarecimento dos mecanismos de reação destes processos. / Triplet carbonyls can be named reactive oxygen species once they behave chemically as alkyloxyl radicals and therefore can potentially drive beneficial and deleterious processes in biological systems. In the case of lipid peroxidation, these species have been found not only to be reaction products but also to amplify the radical chain by hydrogen abstraction of polyunsatured lipid molecules. With the aim of finding efficient and reliable chemical probes for triplet carbonyls, we studied here the quenching properties of conjugated dienes, namely 2,4-hexadienoate and 2,4- pentadienoate anions and corresponding alkyl esters, upon triplet acetone generated either chemically (thermolysis of tetramethyl-1 ,2-dioxetane) or enzymically (aerobic oxidation of isobutanal/horseradish peroxidase). As expected, the quenching rate constants were found to be diffusion controlled, although those for the pentadienoate derivatives were 3-fold lower than those measured for the hexadienoates. Therefore, independently of the presence of allylic hydrogens in the diene probe, the triplet acetone quenching occurred by a physical process followed by cis,trans-isomerization, without hydrogen abstraction from the quencher. The reactivity of the studied dienes towards oxygen reactive species known to be formed during lipid peroxidation, such as singlet oxygen, and peroxyl, hydroxyl and superoxide radicals, was also investigated to assure they would not interfere with the radical lipoperoxidation chain. Indeed, none of the dienes showed antioxidant activity on classical model systems. Preliminary experiments with model systems widely used to study lipid peroxidation showed that the trans, trans-ethyl sorbate can inhibit the mitochondrial swelling induced by enzymically formed triplet benzophenone and to quench the chemiluminescence of microsome preparations challenged with iron/ascorbate. This is in agreement with reported work showing that the lipid peroxidation chain associated with mitochondria permeabilization and polyunsaturated fatty acid peroxidation is amplified by intermediate triplet carbonyl products. Altogether our data indicate that conjugated dienes can be used as specific quenchers of triplet carbonyls formed in biological systems without reacting with other reactive intermediates.

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