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Photochemistry of novel 4-alkylamino benzophenone initiators: a conventional laser flash photolysis and mass spectrometry study

1990; Elsevier BV; Volume: 54; Issue: 3 Linguagem: Inglês

10.1016/1010-6030(90)85009-l

1873-2666

Norman S. Allen, E. Lam, J.L. Kotecha, W.A. Green, Alan Timms, S. Navaratnam, Barry J. Parsons,

Photochemistry and Electron Transfer Studies

Conventional microsecond and nanosecond laser flash photolysis studies have been carried out on 15 novel 4-alkylamino-substituted benzophenone photoinitiators. Using the microsecond technique, ketyl radical formation is observed from all 15 photoinitiators with a half-life longer than that for the ketyl radical of benzophenone. The formation of the radical anion through an intramolecular exciplex is considered to be an important precursor to this reaction. Triplet-triplet absorption decays by a first-order process; this decay is independent of the ground state concentration of the initiator when intramolecular hydrogen atom abstraction is structurally feasible. The solvent is also seen to influence intramolecular hydrogen atom abstraction and it dominates in acetonitrile where pseudo-first-order hydrogen atom abstraction does not occur. Photolysed product analysis using mass spectrometry complies with the conclusions from laser flash photolysis.