Formation and Reactions of Long Lived Xanthene Dye Radicals. II. Photochemical Reduction of Rhodamine‐B and Fluoresceïn Derivatives

Abstract

AbstractIt is reported about the formation and reactions of the semireduced species of methylated fluoresceïn, rhodamine‐B and pyronine. ESR‐measurements have shown that the semireduced methylated fluoresceïn in acetonitrile formed by a reaction between the dye triplet and the leuco‐dye, is a triphenylmethyl type radical. It disappears via a disproportionation reaction, the trimethylated radicals having lifetimes of several months. Oxidation by oxygen leads to the formation of a dye peroxide. The results obtaines with rhodamine‐B are similar to those obtaines with fluoresceïn in aqueous solution (see part I), however, photochemical reactions were only observed after excitation into a higher energy level of rhodamine‐B. These results are compared with those obtained with pyronine.