Reversed triplet mechanism CIDEP in triplet azoalkanes

The CIDEP of transient alkyl radicals, generated by triplet sensitization o f symmetrical azoalkanes, is studied by time-resolved EPR (TREPR) spectrosc opy. The polarization is found to consist of two net components, one reflec ting the polarization of the triplet sensitizer, and the other being attrib utable to a reversed triplet mechanism taking place in the triplet sensitiz ed azo compound. The latter amounts to - 8.4 +/- 1.5 times the Boltzmann po larization for triplet sensitized AIBN at room temperature in benzene. For the benzophenone/AIBN system it is found that spin relaxation in triplet be nzophenone and quenching by AIBN occurs with T-3(1) = (6.4 +/- 1.3) ns and k(q)(T) = (9:3 +/- 0.2) X 10(8) M-1 s(-1) under these conditions. (C) 2000 Elsevier Science B.V. All rights reserved.