Competitive Reactions of Diene Cation Radicals Formed on Irradiated Metal Oxide Surfaces

Article abstract of DOI:10.1016/S0040-4020(01)90277-7

The heterogeneous photochemical oxygenation of conjugated dienes induced by long wavelength UV irradiation of TiO2 powders suspended in oxygenated CH3CN was studied.In nearly all cases, products resulting from the oxidative cleavage of the double bonds were observed, in parallel to that previously reported for monoolefins.A mechanism is proposed which involves the intermediacy of a diene cation radical generated by transfer of an electron from the adsorbed diene to a photogenerated hole localized at the surface of the excited TiO2 particle.Non-oxidative cleavage products are also observed, and the effect of the semiconductor surface in controlling reactivity of the photogenerated cation radical is discussed.The first examples of aromatization and Diels-Alder dimerization mediated by irradiated semiconductor suspensions are presented.