The photoyields of methylviologen cation radical in frozen TiO2 and SnO2 colloids and dihexadecyl phosphate (DHP) anionic vesicles containing RU(bpy)(3)(2+) and methylviologen as electron donor and acceptor are compared. The net yield of charge separation through direct photoelectron transfer from the electron donor to the electron acceptor in DHP vesicles is much lower than that through photoelectron and hole generation inside colloidal semiconductors with their subsequent trapping by the electron acceptor and the electron donor or that through electron transfer from the donor to the acceptor mediated by the semiconductor colloid. In contrast to the electron spin resonance (ESR) detection of methylviologen cation radical, RU(bpy)(3)(3+) cation radical was not detected by ESR in the above systems.