Excited State of Properties of 2-Phenylbenzthiazole and 3-Phenyl-1,2-Benzisothiazole

The excited state behavoir of 2-phenylbenzthiazole and 3-phenyl-1,2- benzisothiazole was examined by laser flash photolysis techniques in order to determine which reaction intermediates preceded their subsequent photochemistry. Both compounds, together with related derivatives, form longlived readily detectable triplet states. Quenching constant with representatives olefins have been determined and the energy transfer equilibrium between 3-phenyl-1,2-benzisothiazole and 1-methylnaphthalene has been examined. The results suggest that olefins and alkynes react with excited states of 2-phenylbenzthiazole and 3-phenyl-1,2-benzisothiazole by 1,2 addition, and no evidence for prior ring opening was obtained.