摘要:

AbstractThe photochemistry of xanthone complexed with cyclodextrins (α‐, β‐ and γ‐CD) in the solid state has been examined by diffuse reflectance laser flash photolysis. The first half‐life for xanthone triplet decreases as the size of the CD cavity increases; long‐lived ketyl radicals are observed in the cases of β‐ and γ‐CD. These changes in photobehavior are attributed to the restrictions on the mobility of included xanthone imposed b

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb01977.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe wavelength dependent fluorescence spectra and bi‐exponential fluorescence decays oftrans‐6‐styrylquinoxaline (6‐StQx) indicate that two conformers exist in equilibrium in solution. When comparing the conformationally restricted analogues (5Me‐6‐StQx and 7Me‐6‐StQx) with 6‐StQx, the short‐wavelength absorbing conformer of 6‐StQx can be assigned to conformer(A) and the long‐wavelength absorbing component to conformer(B). The temperature effects on the fluorescence lifetime indicate that the short‐lived conformer(A) is the more stable conformer in non‐polar solvents, while the long‐lived conformer(B) is the stable component in polar solvents. The results of semiempir‐ical AMI and CNDO/S CI calculations on both the ground and excited states are consistent with the conclusio

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb01978.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe photochemistry of 1,2,3‐indanetrione (1) has been examined in solution at room temperature by steady state and laser flash photolysis. The triplet state of 1 (T = 6.5 μs, δmux, = 360 and 570 nm, in dry acetonitrile) reacts preferentiallyviaan a‐cleavage process followed by a considerably slower loss of carbon monoxide. Triplet 1 shows a remarkably fast hydrogen abstraction rate constant when in the presence of 1,4‐cyclohexadiene (kr= 1.4 times 106M−1s−1) in spite of its low excitation energy (ET= 42 kcal/mol). This behavior can be explained by assuming that the vicinal carbonyls coplanar to the ketyl radical play an important role in its st

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb01979.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe 9,10‐dicyanoanthracene (DCA)‐sensitized photooxygenation of biphenyl derivatives in the presence of Mg(CIO4)2in acetonitrile produces benzoic acid and its derivatives in high yields. In the absence of Mg(CIO4)2, the rates for the consumption of biphenyl derivatives decrease by a factor of 0.5‐0.8, compared with those in the presence of Mg(CIO4)2. In these cases, however, both biphenyls and DCA are oxygenated to give benzoic acids and anthraquinone, respectively, indicating that the addition of Mg(CIO4)2retards the photooxygenation of DCA. With 4‐methylbiphenyl, the photooxygenation proceeds efficiently without added Mg(CIO4)2, and benzene rings and methyl groups are competitively oxygenated to give benzoic acid, 4‐methylbenzoic acid, 4‐phenylbenzoic acid, and 4‐phenylbenzaldehyde. The addition of Mg(CIO4)2facilitates the oxidation of benzene rings, giving benzoic acid and 4‐methylbenzoic acid as major products. These photooxygenations are initiated by a one‐electron transfer from biphenyls to the excited singlet DCA and proceedviathe radical cations of biphenyls and the rad

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb01980.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe degree of polarization around the water pool generated in aerosol‐ OT/hexane/water reversed micelle solutions was studied by monitoring the depolarization of solubilized probe fluorescence. The 5(E)‐styryI‐1, 3‐dimethyl uracil (SDU) used in this study was moderately polar and proved to be solubilized between the interface and hydrocarbon phases in reversed micelle solution by a fluorescence quenching study with hydrophilic and hydrophobic quenchers. The degree of polarization monitored by SDU was parallel with that obtained from the fluorescence depolarization study of hydrophylic probes solubilized in the water pool and interface. A dramatic increase in microviscosity was observed when ω value beca

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb01981.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe photochemistry (Type I and II) of the phototoxic textile dye Disperse Blue 35 (DB‐35) and its purified components has been studied using electron spin resonance in conjunction with spin trapping technique and the direct detection of singlet oxygen (1O2) luminescence. The main components of DB‐35 (which is synthesized by the successive nitration, reduction and methylation of 1,8‐dihydroxy‐anthraquinone) were separated by HPLC and identified by mass spectrometry and 2‐D NMR as 4,5‐diamino‐1,8‐dihydroxyanthraquinone (4,5‐DDHAQ; 62% of total dye) and 2,7‐diamino‐1,8‐dihydroxyanthraquinone (2,7‐DDHAQ; 31% of total dye). Minor components included 2,5‐diamino‐1,8‐dihydroxyanthraquinone (2,5‐DDHAQ) and a monomethylated derivative of either 4,5‐DDHAQ or 2,7‐DDHAQ. Irradiation (624 nm) of 4,5‐DDHAQ and 2,7‐DDHAQ in dimethylsulfoxide resulted in the generation of superoxide which was trapped by 5,5‐dimethyl‐l‐pyrroline‐N‐oxide (DMPO). Visible light irradiation of the components in ethanol generated1O2with the yields decreasing in the following order: 4,5‐DDHAQ>2,5‐DDHAQ>2,7‐DDHAQ. These findings indicate that upon irradiation by visible light DB‐35 can generate active oxygen species which may be res

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb01982.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractZinc complexes of both 20‐trifiuoroacetoxy‐ and 20‐chloro‐pheophorbide‐a methyl ester yield the same isolable 20‐oxonia‐pheophorbide (2b) on irradiation with visible light in methylene chloride for 90 and 10 min, respectively. In the case of the 20‐chloro derivative, the yield amounts to40–50% along with 30% of starting material. Zinc complexes of 20‐trifluoroacetyl‐ and 20‐chloro‐pyropheophorbide‐a methyl ester behave likewise. In aqueous solution, the expected dihydro‐biliverdin derivatives 2 are obtained among other products, some of them display a strong red fluorescence. In the presence of nucleophiles the oxoniachlorin macrocycle is readily cleaved, yielding the corresponding linear tetrapyrroles. Particularly, reaction with cyanide ions leads to biline derivatives, which could serve as intermediates for the synthesis of natural occurring luciferins from bioluminescent plankton. The possible role of some of the above mentioned reactions in connection with chloro

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb01983.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have studied the photochemical quantum yields of singlet oxygen production (using the RNO bleaching method) and superoxide production (using the EPR‐spin trapping method and the SOD‐inhibitable ferricytochromecreduction spectral assay) of kynurenine (Ky),N‐formylkynurenine (NFK), 3‐hydroxykynurenine (3HK), kynurenic acid (KUA), and the flavins, riboflavin (RF) and flavin mononucleotide (FMN). Such a study of the photodynamic efficiencies is important since these compounds appear endogenously in the eye. The singlet oxygen quantum yields of the flavins and KUA are high, while Ky and 3HK generate no detectable amounts of singlet oxygen. The superoxide quantum yields of the sensitizers are low compared to their singlet oxygen, and Ky and 3HK produce no detectable amounts of superoxide. The production of the superoxide radical is enhanced in the presence of electron donor molecules such as EDTA and NADH. These results suggest that the production of oxyradicals in the lens may be modulated by the presence of endogenous electron donor molecules such as the coenzymes NADH and NADPH, which are present in significant amounts in some lenses. They also suggest that Ky and 3HK, which are known to be present in aged lenses, might play a protective rather than a deleterious role in

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb01984.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe quantum yields of singlet oxygen formation (ØΔ) by the quenching of triplet states of organic sensitizers are measured at various concentrations of the sensitizers by using the time‐resolved thermal lens method. Above a certain concentration, ØΔis independent of the sensitizer concentration. Below the threshold, ØΔgradually decreases as the concentration of the sensitizer decreases. The extrapolation of ØΔto zero concentration indicates that singlet oxygen formation is not necessarily dominant in the quenching process even for the3ππ* state

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb01985.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe S0(ground singlet‐state) Raman spectra of theall‐trans, 9‐cis, 13‐cis, 9,9‐cis, 9, 13‐cis,9,13′‐cisand13,13′‐cisisomers of canthaxanthin as well as the T1(lowest‐excited triplet‐state) Raman spectra of theall‐trans, 9‐cis,13‐cis and 9,13‐cis isomers were recorded. In order to reveal the effect of the carbonyl groups at both ends on the carbon‐carbon conjugated system in‐between (in both the S0and T, states), the carbon‐carbon stretching frequencies were compared between isomeric canthaxanthin and p‐carotene: in the S0state, the C=C stretching frequencies of canthaxanthin were lower by3–10 cm−1than those of β‐carotene, indicating increased conjugation in the former. In the T, state, the “C=C” stretching frequencies of canthaxanthin were lower by12–15 cm−1, indicating a large decrease in the “C=C” bond order in the central part of canthaxanthin. Further, the relations of the C=C (S0) and “C=C” (T1) stretching frequenciesvsthe number of carbon‐carbon double‐bonds were examined for the above two and additional five carotenoids. The result indicated that the terminal carbonyl groups of canthaxanthin are incorporated in the carbon‐carbon conjugated system in the T, state, but that they are almost independent of it in the S0state. Both observations support the idea that the “triplet‐excited

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb01986.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY