Kinetics and mechanism of photoinduced charge separations in the presence of surfactants

Abstract

Photoinduced electron transfer from a sensitizer to an electron acceptor has been investigated in water and in the presence of either negatively charged dihexadecyl phosphate, DHP, or positively charged dioctadecyldimethylammonium chloride, DODAC, surfactant vesicles by steady-state photolysis, fluorescence quenching, and nanosecond laser flash photolysis. Four different substrate-surfactant vesicle organizations have been used. In System I, Ru(byp)(,3)('2+) was attached to the outer and MV('2+) was placed onto the inner surfaces of DHP vesicles. In System II, MV('2+) was attached to the outer and Ru(byp)(,3)('2+) to the inner surfaces of DHP vesicles. In System III, Ru(byp)(,3)('2+) and MV('2+) were localized on the outer surfaces of DHP vesicles. In System IV, both Ru(byp)(,3)('2+) and MV('2+) were localized on the inner surfaces of DHP vesicles. Extremely efficient electron transfers have been observed on the surfaces of surfactant vesicles in Systems III and IV. Electron transfer from excited Ru(byp)(,3)('2+) to MV('2+) across bilayers of vesicles in the presence of externally added EDTA in System I resulted in the formation of reduced methylviologen, MV('+) with a quantum efficiency of 2.4 x 10('-2). Inclusion of PtO(,2) in vesicles interiors in System I lead to hydrogen evolution. Various mechanisms underlying photochemical reactions have been proposed using experimental rate parameters, calculated energetics, and detailed balancing procedures.