Mechanism of pyrene photochemical oxidation in aqueous and surfactant solutions

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-pyren equinones 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 effec ts of oxygen and HSCl2 on the photolysis are interpreted as ruling out mech anistic involvement of a triplet state of pyrene, l-Hydroxypyrene is identi fied as a product of the initial photochemical oxidation. In the optically dilute aqueous solutions, l-hydroxypyrene undergoes further photochemical o xidation to produce 1,6- and 1,8-pyrenequinones. Pyrene photolysis quantum yields are decreased by a factor of approximately 2 in the micellar media r elative to the quantum yields determined in water. Fluorescence data sugges t that pyrene resides in the micelles among the polyoxyethylene portion of the surfactant and not within the core of the micelle.