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

Abstract

The photoinduced dissociation of the carbon–sulfur bond in benzyl-α-naphthyl sulfide (BNS) in acetonitrile has been studied by laser flash photolysis. Upon direct photoexcitation of BNS, C–S bond fission occurs in the excited singlet state, resulting in the formation of the α-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 (T₁) of BNS and the radicals. The efficiencies of the formations of the T₁ state and the radicals are 0.53 and 0.41, respectively. 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-linearly with increasing concentration of the ketone. The second cleavage can be interpreted by considering the formation of the triplet exciplex which consists of triplet BNS and ketone. The mechanism of the efficient C–S bond dissociation ia the triplet exciplex is discussed.