Determination of S*-T Transition Probabilities of Some Xanthene and Thiazine Dyes on the Basis of T-Energy Transfer. II. Results in the Aqueous Solution

Intersystem crossing probability for fluorescein, eosin, erythrosin, methylene blue and thionine in the aqueous solution of pH 7.2 (only for fluorescein 0.05n NaOH solution) has been determined by comparing the quantum yield of the nonsensitized (Φ) and the sensitized photo-reduction (ΦS) on the basis of the relations Φ=βA ΦS=βγA, where βA is the fraction of triplet dye molecules that undergo reduction, and are respectively for acceptor (dye) and donor (sensitizer), and γ is the energy transfer efficiency. This was assumed as unity. ATU and EDTA were used as a reducing agent. 1,5-Naphthalenedisulfonic acid and 1-anthracenesulfonic acid were used as sensitizers. The above relations and assumption have been found to hold satisfactorily. The values for two sensitizers were determined using erythrosin as a reference substances for which was assumed to be unity. obtained was 0.88 for 1,5-naphthalenedisulfonic acid, and 0.82 for 1-anthracenesulfonic acid. values for dyes obtained were: fluorescein (0.021) eosin (0.64) erythrosin (1.0) methylene blue (0.52) thionine (0.55). Using these values, the rate constants for the following elementary reactions have been evaluated (A, dye: RH2 reducing agent): AT+RH2→reaction, AT+RH2→deactivation, AT+A→reaction or deactivation.