Laser Photolysis Study of Triplet Eosin and Thionine Reactions in Photosensitized Oxidations

Abstract —Nanosecond laser photolysis was used to determine the rate constants of quenching (including chemical reactions) of the triplet states of eosin and thionine, at pH 7, by imidazole, l‐histidine, l‐methionine, l‐phenylalanine, l‐tryptophan, 3‐indole‐acetic acid, cytidine, guanosine, α‐chymotrypsin, lysozyme, allylthiourea, thiourea, p ‐nitrosodimethylaniline, I ‐ N 3 ‐ and Fe(CN) 6 4‐ . The quenching rate constants for thionine were found to be up to three orders of magnitude higher than those for eosin. The mechanism of photosensitized oxygenations (free radical vs singlet oxygen) is discussed on the basis of the present results.