Semiconductor Photocatalysis: Reaction Mechanisms for the Photoreductive cis-trans Isomerization of Electron-Deficient Alkenes Catalyzed by CdS Powder

Article abstract of DOI:10.1246/bcsj.66.2461

Highly pure commercially available CdS powder (99.999percent) catalyzes the effective cis-trans photoisomerization of electron-deficient alkenes under visible light irradiation using triethylamine (TEA) as an electron donor, accompanying the formation of the dihydro compound as a two-electron reduction product.The photoisomerization does not occur at all in the absence of TEA.Donor effect, solvent effect, deuterium incorporation experiments for photocatalysis, and MOPAC molecular orbital calculation (MNDO/PM3) of the intermediary radical anions from the alkenes were investigated in order to elucidate the mechanism of this photoisomerization.These results reveal that the CdS-catalyzed cis-trans photoisomerization should proceed through two pathways involving the photoreduction of alkenes: one through the back electron transfer from the radical anion of the alkene (alkene radical anion) towards the radical cation of TEA (TEA radical cation), both formed by photoexcited conduction band electrons and holes of CdS, respectively.The other is the reoxidation of a radical intermediate (alkyl radical), formed by protonation of alkene radical anion, by TEA radical cation.