Picosecond flash photolysis of high-speed photoinitiator systems

The sensitization mechanism of a sensitizer dye, 2-[p-(diethylamino) styryl ]naphtho[1,2,d]thiazole (DNT), with a radical-generating reagent, 3,3',4,4' -tetrakis(tert-butyldioxycarbonyl)benzophenone (I), in toluene has been inv estigated by picosecond laser flash photolysis. In the absence of I, the fl uorescence of DNT with a decay time of 100 ps,a rapidly decaying transient absorption with a decay time of 100 ps corresponding to the decay time of t he fluorescent singlet excited state, and an unknown slowly decaying absorp tion with a decay time of 6 ns were detected. However, no transient absorpt ion of the triplet was detected. In the presence of I, the rapidly decaying absorption and fluorescence were not quenched by I, but the slowly decayin g absorption was quenched at a quenching rate k(q) = 5 x 10(10) dm(3)/mol s , which was almost the same as the diffusion-controlled rate. The results s uggested that the sensitization of I proceeded from the non-radiative trans ient state of DNT with a decay time of 6 ns in toluene.