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.