Valence Isomerization of Quadricyclene Mediated by Illuminated Semiconductor Powders

Article abstract of DOI:10.1021/jo00391a022

Quadricyclene undergoes valence isomerization to norbornadiene in the presence of photoexcited n-type semiconductor powders.For samples irradiated under comparable conditions of time and intensity, the yield of the diene product varies with (i) the semiconductor in the order CdS > TiO2 > ZnO and (ii) the solvent in the order dichloromethane > acetonitrile > tetrahydrofuran.The presence of oxygen in a sample diminishes the product yield, whereas both methylviologen dication and diphenylamine enhance the yield.The quantum efficiency of norbornadiene production appearsto be rather low (ca. 10^-2 for CdS) in these heterogeneous systems.These observations are interpreted in terms of the redox chemistry that results upon interaction of the photogenerated electron-hole pairs in the semiconductor with the surrounding organic medium.