Laser photolysis studies of the carbon-sulfur bond cleavage induced in thetriplet exciplex of benzylnaphthyl sulfide and aromatic ketones

The photoinduced dissociation of the carbon-sulfur bond in benzyl-alpha -na phthyl sulfide (BNS) in acetonitrile has been studied by laser flash photol ysis. Upon direct photoexcitation of BNS, C-S bond fission occurs in the ex cited singlet state, resulting in the formation of the alpha -naphthylthiyl and benzyl radicals with a quantum yield of 0.22. Triplet sensitization of BNS by xanthone and benzophenone causes the simultaneous formation of the lowest triplet state (T-1) of BNS and the radicals. The efficiencies of the formations of the T-1 state and the radicals are 0.53 and 0.41, respective ly. When triplet BNS decays, further formation of the radicals is observed with an efficiency of 0.95. The decay rate of triplet BNS is enhanced non-l inearly with increasing concentration of the ketone. The second cleavage ca n be interpreted by considering the formation of the triplet exciplex which consists of triplet BNS and ketone. The mechanism of the efficient C-S bon d dissociation via the triplet exciplex is discussed.