Novel intermolecular and intramolecular photochemical reactions initiated by excited state single electron transfer processes

Several examples of photoinduced electron transfer initiated cation radical carboncarbon bond fragmentation reactions are reported. 1,2-aminoalcohols and 1,2-diamines undergo analogous fragmentation reactions although they show quite different reactivities. In general, the cation radicals of 1,2-diamines fragment more efficiently than those of aminoalcohols and the reactions are not dependent on the basicity of the reduced acceptor counterion species. A systematic study of 1,2-diamines indicates that the quantum efficiencies of the reaction are highly dependent on the reaction conditions (solvent, type of sensitizer, cosensitization, etc.) and structural considerations of the molecules being studied. Higher quantum efficiencies can be obtained using a triplet sensitizer or cosensitization. The effects of molecular orbital alignment on the efficiency of fragmentation were analyzed by modifying the structures of the 1,2-diamines. Interestingly, higher quantum yields are observed when certain molecular orbital configurations are achieved. Similar conclusions are obtained from studies of the reactivity of "remote" aminoalcohols and diamines. In this report, we also demonstrate that the quantum efficiency of the cation radical fragmentation can be improved dramatically by utilizing an efficient fragmentable electron acceptor as sensitizer (such as carbon tetrachloride). A new concept of "double fragmentation" is proposed.