The S2 → S1 internal conversion of benzophenone and p-iodobenzophenonel

Two modes of excitation (S-0 --> S-2 and S-0 --> S-1) of benzophenone (BP) and p-iodobenzophenone (p-IBP) in acetonitrile have been examined by ultrafast pump-probe experiments. The S-1 states (lambda(max) similar to 575-580 nm) of BP and p-IBP were observed to be generated with lifetimes of 0.53 and 0.59 ps, respectively, following excitation at 267 nm, and this has been attributed to the S-2 --> S-1 internal conversion. The rates of the S-1 --> T-1 ISC have been observed to be similar following either 267 or 335 nm excitation for both BP (similar to1 x 10(11) s(-1)) and p-IBP (similar to2.3 x 10(11) s(-1)).