Electron spin resonance studies on the photodissociation of 2,4,6-trimethylbenzoyldiphenylphosphine oxide

Abstract

Upon irradiation of 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TMDPO) with u.v. light in O₂-free benzene solution a doublet indicative of phosphorus-centred radicals was observed. By this technique α-scission of TMDPO yielding the diphenylphosphinoyl radical (Ph₂ṖO) was directly evidenced. This radical was found to add to the carbonyl groups of intact TMDPO with k= 1.6 ± 10⁷M^–1s^–1 forming a radical of the general structure A[Ph₂P(O)]ĊOP(O)Ph₂(A: 2,4,6-trimethylbenzoyl). In the time-resolved measurements CIDEP due to the radical-pair mechanism was observed.