ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE (SWITZERLAND)
Apparent rate constants and quantum yields have been determined for the rose bengal sensitized photooxidation of 10-methyl phenothiazine in methanol and in OW and WO microemulsions. A Stern-Volmer analysis of the luminescence of singlet oxygen in solutions of CD3OD containing different concentrations of the phenothiazine in derivative revealed a very efficient quenching of the triplet-state of rose bengal by the substrate. Evaluation of rate constants and local concentrations of sensitizer and substrate leads to the conclusion that the rather low quantum yields of photooxidation of 10-methyl phenothiazine in the three media investigated is mainly due to the efficiently competing deactivation of the triplet state of the sensitizer by the substrate. For decontamination purposes, photochemically initiated singlet oxygen reactions may not be recommended due to the many efficient deactivating processes of singlet oxygen and of the triplet state of the sensitizer.