Transient Measurements of Photochemical Processes in Dyes. I. The Photosensitized Oxidation of Phenol by Eosin and Related Dyes

Abstract

Irradiation of the fluorescein dyes in their visible absorption bands excites metastable triplet states which decay by the bimolecular reaction of triplet molecules. A rapid reaction of phenol with triplet eosin is shown by the retardation of the rate of aerobic photobleaching and an acceleration of the rate of triplet disappearance. The primary photochemical reaction between phenol or phenolate ion with the triplet dye produces a phenoxy free radical and a reduced dye free radical, which disappear in second-order processes. Numerical values are given for the rate constants of several elementary reactions. The competition between physical quenching and charge-transfer chemical reaction can be explained by spin-conserving processes.