Mechanism of Pyrene Photochemical Oxidation in Aqueous and Surfactant Solutions

Abstract

The photolysis of pyrene has been studied in water and in Brij 35 micellar media. Photolysis in both media lead to the formation of 1,6- and 1,8-pyrenequinones as stable products. The first step in the photochemical oxidation is proposed to involve an electron transfer from the excited singlet state of pyrene to molecular oxygen in a contact charge-transfer pair. The effects of oxygen and HgCl2 on the photolysis are interpreted as ruling out mechanistic involvement of a triplet state of pyrene. 1-Hydroxypyrene is identified as a product of the initial photochemical oxidation. In the optically dilute aqueous solutions, 1-hydroxypyrene undergoes further photochemical oxidation to produce 1,6- and 1,8-pyrenequinones. Pyrene photolysis quantum yields are decreased by a factor of approximately 2 in the micellar media relative to the quantum yields determined in water. Fluorescence data suggest that pyrene resides in the micelles among the polyoxyethylene portion of the surfactant and not within the core of the micelle.