Oxygen uptake induced by electron transfer from donors to the triplet state of methylene blue and xanthene dyes in air-saturated aqueous solution

The effects of oxygen in the photolysis of rose bengal, eosin, erythrosin and methylene blue were studied in the presence of formate and electron donors, such as ascorbic acid, aromatic amino acids or aliphatic amines, e. g. triethylamine (TEA). The overall reaction is conversion of oxygen via the hydroperoxyl/superoxide ion radical into hydrogen peroxide. The quantum yield of oxygen uptake (Phi-o(2)) increases with the donor concentration. The photoinduced formation of H2O2 is initiated by quenching of the triplet state of the dye by the donor and subsequent reactions of both the dye and donor radicals with oxygen. For methylene blue and the xanthene dyes in the presence of 10 mM ascorbic acid or 0.1 M TEA Phi-o(2) = 0.07-0.25. The spectral and kinetic properties of the specific dye transients, including the radicals involved and the pH and concentration dependences, are discussed.