Kinetics of the heterogeneous electron transfer reaction of triplet pyrene in micelles to Br2− radicals in aqueous solution

✍ Scribed by A. J. Frank; M. Grätzel; A. Henglein; E. Janata

• Publisher: John Wiley and Sons
• Year: 1976
• Tongue: English
• Weight: 454 KB
• Volume: 8
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550080604

✦ Synopsis

A combined flash photolysis and pulse radiolysis experiment was carried out to produce triplet pyrene (P) molecules in micelles of cetyltrimethylammonium bromide and Brtin the surrounding aqueous medium. The reaction 3Pmie + Bryaq + PA,c + 2 Brwas followed by optical absorption measurements in the 10-8-10-4-sec range. This reaction possesses a "fast" and a "slow" component wit.h respective rate constants of 2.3 X lo6 sec-l and 1 X 109.M-1 . sec-l.

The fast component is related to the probability of a Brqradical meeting a triplet pyrene containing micelle on the first encounter (only lSyc of the micelles contained a triplet. molecule). Reactions involving more than one Brqradical-micelle encounter are ascribed to the slow component. The presence of two components reflects the fact, that the residence time of a Brlradical in the vicinit,y 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 energet.ics of this electron transfer reaction are also presented.