NOVEL INTERMOLECULAR AND INTRAMOLECULAR PHOTOCHEMICAL-REACTIONS INITIATED BY EXCITED-STATE ELECTRON-TRANSFER PROCESSES

Several examples of photoinduced electron transfer initiated cation ra dical carbon-carbon bond fragmentation reactions are reported. 1,2-ami noalcohols and 1,2-diamines undergo analogous fragmentation reactions although they show quite different reactivities. In general, the catio n radicals of 1,2-diamines fragment more efficiently than those of ami noalcohols and the reactions are not dependent on the basicity of the reduced acceptor counter-ion species. A systematic study of 1,2-diamin es indicates that the quantum efficiencies of the reaction are highly dependent on the reaction conditions (solvent, type of sensitizer, cos ensitization, etc.) and structural considerations of the molecules bei ng studied. Higher quantum efficiencies can be obtained using a triple t sensitizer or cosensitization. The effects of molecular orbital alig nment on the efficiency of fragmentation were analyzed by modifying th e structures of the 1,2-diamines. Interestingly, higher quantum yields are observed when certain molecular orbital configurations are achiev ed. Similar conclusions are obtained from studies of the reactivity of ''remote'' aminoalcohols and diamines. In this report, we also demons trate that the quantum efficiency of the cation radical fragmentation can be improved dramatically by utilizing an efficient fragmentable el ectron acceptor as sensitizer (such as carbon tetrachloride). A new co ncept of ''double fragmentation'' is proposed.