Photoinduced and redox-induced transmembrane processes with vesicle-stabilized colloidal cadmium sulfide and multicharged viologen derivatives

Colloidal cadmium sulfide (CdS) and methylviologen (MV²⁺) or new viologen derivatives carrying more positive charges were placed at specific sites of dihexadecyl phosphate (DHP) vesicles. Benzyl alcohol was used as a sacrificial electron donor to promote reduction of the viologens by photoexcited CdS colloid majority carriers. Transmission electron microscopy, ¹³C nuclear magnetic resonance, and differential scanning calorimetry were used for physical characterization. Photochemical events were followed by in situ optical and electrochemical monitoring. Redox-induced transmembrane diffusion, which had been found with MV²⁺, could be reduced by a factor 18 by using a triply charged viologen derivative and by a further factor of 30 in a configuration involving transmembrane electron transfer. In that case the quantum yield was ca. 0.05 at 410 nm, while virtually no reduced viologen leaking could be observed during at least 10 min. Physical evidence was found for a partial penetration of the CdS colloids into the DHP membrane.