Kinetics of fast reactions of triplet states and radicals under photolysis of 4,4′-dimethylbenzophenone in the presence of 4-halophenols in micellar solutions of sodium dodecyl sulfate in magnetic field |
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Authors: | P P Levin N B Sul'timova O N Chaikovskaya |
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Institution: | (1) N. M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 4 ul. Kosygina, 119991 Moscow, Russian Federation;(2) Siberian Physical Technical Institute, Tomsk State University, 1 pl. Novosobornaya, 634050 Tomsk, Russian Federation |
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Abstract: | Quenching kinetics of the 4,4′-dimethylbenzophenone triplet state with para-substituted phenol derivatives RC6H4OH (R = H, F, Cl, Br, I) was studied by nanosecond laser photolysis in aqueous micellar solutions of sodium dodecyl sulfate.
The kinetic data were processed in the framework of a model with the Poisson distribution of phenols between micelles. The
partition constants of RC6H4OH between the aqueous and micellar phases and the rate constants of their escape from a micelle and quenching of the 4,4′-dimethylbenzophenone
triplet state with phenols in micelles were obtained. The quenching proceeds with high rate constants through hydrogen atom
transfer to form the ketyl and phenoxyl radicals (no radicals are formed in the case of 4-iodophenol), which then recombine
in a micelle or escape into the outer aqueous volume. The application of an external magnetic field retards radical pair recombination
in a micelle and increases the fraction of radicals escaped into the aqueous phase. The quantum yield of radical pairs decreases
2.5-fold, and the rate of their recombination in micelles increases 2.5-fold on going from 4-chloro- to 4-bromophenol. This
is caused by the acceleration of triplet radical pair recombination in the solvent cage.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1391–1396, June, 2005. |
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Keywords: | 4 4′ -dimethylbenzophenone 4-halophenol laser photolysis triplet states hydrogen atom transfer radical recombination heavy atom effect magnetic effect |
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