Homolytic cleavage of C-Si bond of p-trimethylsilylmethylacetophenone upon stepwise two-photon excitation using two-color two-laser flash photolysis

C-Si bond cleavage of p-trimethylsilylmethylacetophenone(1) occurred in a higher triplet excited state (Tn), giving mainly p-acetylbenzyl radical with the transient absorption in the region of 295-360 nm, with a quantum yield of 0.046 ± 0.008 using the two-color two-laser photolysis techniques. In contrast, the C-Si bond cleavage of p-trimethylsilylmethylbenzophenone(2) was absent in the Tn state whose energy is larger than the C-Si bond cleavage energy. The results can explain existence of a bond cleavage crossing between potential surfaces of the Tn state and a dissociative state of the C-Si bond for 1, but not for 2.