An E.S.R. study of radical intermediates in the photoreduction of xanthene dyes

Abstract

E.s.r. spectra are reported for the semireduced radicals of fluorescein, eosin Y, and rose bengal B, formed during the photolysis of these dyes in alcohol solutions of various indole derivatives and triethylamine. When indoleacetic acid is used as substrate, the dye radicals exist as the diprotonated monoanion radicals, with OH proton splitting constants varying from 0.12 G (fluorescein) to 1.0 G (rose bengal B). In the presence of tryptamine or triethylamine the intermediate dye radicals exist as the unprotonated radical trianions. The e.s.r. spectrum of the semireduced monoanion radical of rhodamine B was also observed during photolysis of the dye in the presence of triethylamine.