Light-induced redox reactions of proflavine in aqueous and micellar solution

Abstract

Primary photoprocesses and photochemical behavior of proflavin (PF) were investigated in aqueous and anionic micellar solution. Micellar effects are noted in the pK of the singlet and triplet excited states, which are due to differences in surface and bulk pH. The photoredox behavior is distinguished by (1) a monophotonic photoionization process and T-T annihilation leading to production of oxidized and reduced proflavin radicals in water solution, and (2) a biphotonic photoionization process in NaLS solution. Because of strong adsorption of PF on the surface of anionic micelles, the T-T annihilation is impaired in the surfactant solutions. Reduced PF radicals are also produced in aqueous solution in the presence of triethanolamine, where reductive quenching of the triplet states is dominant. They are distinguished by a long lifetime and a high reactivity toward colloidal platinum. The kinetics of intervention of this catalyst in the radical reaction is illustrated directly. 8 figures.