Photochemical electron transfer in micellar systems and across surfactant vesicle bilayers promoted by esters of 2,1,3-benzothiadiazole-4,7-dicarboxylic acid

Abstract

The dibutyl (BTDB) and diethyl (BTDE) esters of 2,1,3-benzothiadiazole-4,7-dicarboxylic acid have been prepared (BTDB for the first time) and used in the transfer of electrons from morpholine ethene sulfonic acid (MESH) to 1,5-anthraquinone disulfonate (AQDS) in cetyltrimethylammonium bromide (CTAB) micelles, or across vesicle bilayers prepared from dioctadecyldimethylammonium bromide (DODAB). BTDB and BTDE act as light absorbers and then accept an electron directly from MES^– before passing it to AQDS. Kinetic studies indicate that the rate determining step in micelles is the electron transfer from BTDB^–˙ to AQDS, whilst in the vesicle system, at low concentration it is either the same step or diffusion of BTDB^–˙ across the vesicle bilayer. At higher concentrations, the rate of electron transfer across the vesicle is independent of all [reagents] except H⁺, so we tentatively conclude that the rate determining step is charge compensating diffusion of H⁺ across the bilayer.