Time-resolved EPR and laser photolysis investigations of photoinduced omega-bond dissociation in an aromatic carbonyl compound having triplet pi,pi* character

摘要

Photochemical properties of photoinduced omega-bond dissociation in p-phenylbenzoylbenzyl phenyl sulfide (PPS) having the lowest triplet state (T-1) of pi,pi* character in solution were investigated by time-resolved EPR and laser flash photolysis techniques. PPS was found to undergo photoinduced omega-bond cleavage in the excited lowest singlet state (S-1(eta,pi*)) with it quantum yield (Phi(rad)) of 0.15 for the radical formation, which was independent of excitation wavelengths. Based on the facts of the observation of the absorption spectrum of triplet PPS upon triplet sensitization of xanthone, and absence of CIDEP signal, omega-cleavage was shown to be absent in the T-1(pi,pi*) state of PPS. Considering the electronic character of the excited and dissociative states of PPS, a schematic energy diagram for the w-bond dissociation of PPS was shown. (c) 2005 Elsevier B.V. All rights reserved.