Mechanism of the Direct and Triplet-sensitized Photolysis of N-(1-Naphthoyl)-O-(p-toluoyl)-N-phenylhydroxylamine

Article abstract of DOI:10.1246/bcsj.58.2875

Quantum yields (Φ) were determined for benzophenone-sensitized and direct photolysis of the title hydroxylamine (NT).Analysis of linear Stern-Volmer plots of the reciprocal of Φ against the reciprocal of NT concentration reveals that the sensitized decomposition of NT takes place via its first triplet excited state (T₁) produced by triplet-triplet energy transfer from benzophenone to NT.The fact that the quantum yields for the direct photolysis are independent of NT concentration indicates no occurence of both self-quenching and induced decomposition of NT by the photochemically generated radicals.Closer examination of the micellar and solvent viscostity effects on the quantum yields for the direct photolysis with 313-nm light shows the existence of at least two spin-correlated (singlet) radical pairs: One is a contact radical pair whose recombination eventually yields 1,3-toluoyloxyl-migrated product and the other a solvent-separated radical pair from which 1,5-toluoyloxyl-migrated product is derived in competition with diffusive escape from the solvent or micelle cage.Exclusive occurence of the direct photolysis from the first singlet excited state (S₁) was explained on the basis of the large energy gap between S₁ and T₁ (31 kcal mol^-1) which is likely to make intersystem crossing from S₁ to T₁ very inefficient.