Energy transfer, electron transfer, and addition reactions of triplet state of 1,3-dihydroimidazole-2-thiones investigated by laser flash photolysis

Article abstract of DOI:10.1246/bcsj.72.339

The transient absorption bands observed at ca. 400 and 550 nm for 1,3- dihydro-2H-imidazole-2-thione (IT), 1,3-dihydro-1-methyl-2H-imidazole-2- thione (MIT), and 1,3-dihydro-2H-benzimidazole-2-thione (BIT) have been assigned to their triplet states (³IT* 's) by the quenching and sensitizing experiments using laser flash photolysis technique. Short intrinsic triplet lifetimes and relatively high triplet energies have been evaluated as characteristics of ³IT* 's. For electron acceptors, photoinduced electron- transfer reaction occurs via ³IT* 's in the diffusion controlled limit. The nucleophilic character of ³IT* 's was confirmed by changing the substituents of alkenes on the addition reactions. MO calculations indicate that the lowest electronic configurations of both ³IT* and ³MIT* have ³(n,π*) character, while ³BIT* has ³(π,π*) character. The addition reactivity of ³BIT* is slightly higher than those of ³IT* and ³MIT*, which is opposite to the general tendency.