Photoreduction of methyl viologen sensitized by sulphonated phthalocyanines in micellar solutions

Abstract

When sulphonated derivatives of zinc(II) phthalocyanine (ZnSP), palladium(II) phthalocyanine (PdSP) and zinc(II) naphthalocyanine (ZnSN) are incorporated into cationic micelles, these dyes can sensitize the reduction of methyl viologen (MV²⁺) by cysteine with red light (600–780 nm). The quantum yields for these reactions are low; 0.01 (PdSP), 0.001 (ZnSP) and 0.004 (ZnSN) mol ein^–1. In the absence of micelles the dyes form photoinactive aggregates which do not sensitize the reduction of MV²⁺. Flash photolysis and fluorescence studies indicate that the reaction results primarily from reductive quenching of the phthalocyanine by cysteine, although in the case of ZnSN oxidative quenching of the triplet state by MV²⁺ also occurs.