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Kinetics of the heterogeneous electron transfer reaction of triplet pyrene in micelles to Br 2 − radicals in aqueous solution
Author(s) -
Frank A. J.,
Grätzel M.,
Henglein A.,
Janata E.
Publication year - 1976
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550080604
Subject(s) - chemistry , micelle , radiolysis , flash photolysis , photochemistry , reaction rate constant , radical , solvated electron , kinetics , aqueous solution , pyrene , bromide , electron transfer , cationic polymerization , organic chemistry , physics , quantum mechanics
A combined flash photolysis and pulse radiolysis experiment was carried out to produce triplet pyrene (P) molecules in micelles of cetyltrimethylammonium bromide and Br 2 − in the surrounding aqueous medium. The reaction 3 P mic + Br → P mic ++ 2 Br − was followed by optical absorption measurements in the 10 −8 −10 −4 –sec range. This reaction possesses a “fast” and a “slow” component with respective rate constants of 2.3 × 10 6 sec −1 and 1 × 10 9 M −1 · sec −1 . The fast component is related to the probability of a Br 2 − radical meeting a triplet pyrene containing micelle on the first encounter (only 16% of the micelles contained a triplet molecule). Reactions involving more than one Br 2 − radical–micelle encounter are ascribed to the slow component. The presence of two components reflects the fact that the residence time of a Br 2 − radical in the vicinity of a cationic micelle is substantially longer than the diffusion time of the radical between micelles. Thus the conditions met in micellar chemistry differ dramatically from those in ordinary solution kinetics where the encounter time is generally much shorter than the time between encounters. Some considerations on the energetics of this electron transfer reaction are also presented.