Photochemistry of benzophenone in aliphatic amines studied by laser photolysis in the temperature range 300-77 K

Abstract

Laser photolysis studies of benzophenone in both sec-butylamine and triethylamines were carried out in the temperature range 300-77 K. For the sec-butylamine solution of benzophenone, the transients observed after laser pulsing are found to be the ketyl and anion radicals of benzophenone. The ratio of the yield for the formation of ketyl radical to that of the anion radical is markedly dependent on temperature: the ketyl radical is the major product at high temperatures while the anion radical becomes predominant at low temperatures. On the other hand, the triethylamine solution of benzophenone gives solely the ketyl radical as a photoproduct in the temperature range studied. The photochemical reaction of benzophenone in both sec-butylamine and triethylamine is markedly suppressed on going from high to low temperatures. These results are discussed in detail on the basis of the photochemical reaction mechanism involving the formation of the triplet charge-transfer complex (i.e., triplet exciplex) between triplet benzophenone and an amine molecule. The solvent effects on the photoreaction are also discussed.