Photosensitized Reduction of Methyl Viologen Using Eosin-Y in Presence of a Sacrificial Electron Donor in Water-Alcohol Mixture

Abstract

Photoreduction of methyl viologen (MV2+) by eosin-Y (EY2−) in the presence of triethanolamine (TEOA) has been investigated in water–methanol mixture by means of steady-state photolysis and laser-flash photolysis in the visible/near-infrared regions. The complete conversion to the persistent methyl viologen radical cation (MV·+) was observed in the presence of lower concentrations of EY2− and excess TEOA. By laser-flash photolysis measurements, electron transfer was confirmed to occur from the triplet state of EY2− [3(EY2−)*] to MV2+ in the rate constants of ca 2.0 × 1010M−1 s−1. The rates and efficiencies of production of MV·+ were found to be dependent on solvent compositions and concentrations of MV2+ ionic salt and TEOA. The back electron transfer reaction from MV·+ to EY·− was retarded in the presence of TEOA, which supports that EY2− is reproduced by accepting an electron from TEOA. In the presence of excess TEOA, the indirect formation of MV·+ from EY·3− which was produced by accepting an electron from TEOA, was confirmed. The contributions of both the oxidative and reductive routes of 3(EY2−)* for the MV·+ formation have been confirmed.