Comparative study on the interfacial electron transfer of zinc porphyrins with meso-π-extension at a 2(n) pattern

Three zinc-tetraarylporphyrins were prepared in order to investigate the effects of systematic meso-π-extension on the redox behaviors and interfacial electron transfer kinetics. The meso-π-extension increased at a 2(n) pattern, where 2(n) was the benzene ring number in an aryl group and the aryl group represented phenyl, naphthyl and pyrenyl group, respectively. The structures of zinc-tetraarylporphyrins and hydroquinone were optimized by using density functional theory. The bimolecular reactions between zinc-tetraarylporphyrins and hydroquinone at the liquid-liquid interface were studied by using scanning electrochemical microscopy. There was an inverse electron transfer rate-overall driving force dependence by comparison of three bimolecular reactions. It was suggested that the formation of a precursor between zinc-tetraarylporphyrin cation and hydroquinone was deeply influenced by the increasing steric hindrance from phenyl group to pyrenyl group. The electron transfer rate constant depended strongly on the overall driving force for each bimolecular reaction, with transfer coefficients of 0.41, 0.37 and 0.39.