Factors affecting dye-sensitised photo-oxygenation reactions

Abstract

The kinetics of dye-sensitised oxidation reactions are considered. Utilisation of rate of oxygen absorption measurements to provide information on light intensity and the quantum yield of triplet formation of the dye, is discussed. The way in which solvent isotope effects, sensitiser–substrate triplet–triplet energy transfer processes, and quenching of the sensitiser excited singlet state by the substrate affect the kinetics is considered. Quantitative measurements on the quenching of the excited singlet states of Methylene Blue and Rose Bengal by anions, β-carotene, and 2,5-diphenylisobenzofuran are reported. A comprehensive rate expression is obtained for oxidation reactions in which the substrate interacts with the excited singlet and triplet states of the sensitiser, and with singlet oxygen.