pH-dependent photoinduced electron transfer at the gold electrode modified with a self-assembled monolayer of a porphyrin-mercaptoquinone coupling molecule

A porphyrin-quinone coupling molecule with a thiol group was synthesized and immobilized on a gold electrode by the self-assembly method. In electrolyte solutions containing methylviologen as an electron acceptor and EDTA as an electron donor, anodic and cathodic photocurrents were observed at potentials respectively more positive and more negative than the redox potential of the quinone moiety. When the pH of the solution was changed, the redox potential of the quinone moiety shifted to the more negative direction and, accordingly, the potential dependence of the photocurrents also shifted to the negative direction, indicating that the photoinduced electron transfer direction can be controlled by the pH in the electrolyte solution. (C) 1997 Elsevier Science S.A.