Photochemistry of substituted benzyldiphenylphosphine oxides

Photochemical reactions (lambda irr = 254 nm) of substituted benzyldiphenylphosphine oxides 1a-e have been investigated in benzene and acetonitrile. alpha-Cleavage from the singlet excited state is proposed as the primary process, and products formed both before and after escape of the primary intermediates from the solvent cage result. Radicals 2 and 3 are observed by nanosecond flash photolysis following excitation of 1a at 266 nm in acetonitrile. Acetone sensitization of 1a,b fails to improve the efficiency of product formation. The quantum yields of disappearance of 1a,b are unaffected by O2, and mechanisms for product formation from 1a in the presence of oxygen are proposed.