Supramolecular semiconductor receptor assemblies: Improved electron transfer at TiO2-β-cyclodextrin colloid interfaces

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Abstract
Semiconductor TiO2-colloids are stabilized by ß-cyclodextrin (ß-CD). Photoinduced electron transfer at the semiconductor (S.C.) solution interface is controlled in the S.C.-receptor assembly TiO2-β-CD. Trapping of TiO2-ß-CD photoexcited conduction-band electrons by N,N’-dioctyl-4,4’-bipyridinium, C8V2+, is 4.4 fold more effective than by N,N’-dimethyl-4,4’-bipyridinium. The kinetics of C8V2+ reduction, inhibition experiments and laser flash photolysis studies reveal that the effective trapping of conduction-band electrons by C8V2+ originates from its association to the ß-CD receptor. Electron transfer from dye, proflavine, Pfl, to the S.C., is similarly controlled by the S.C.-receptor assembly. In the presence of the Pt modified semiconductor-receptor colloid, Pt-TiO2-ß-CD, effective photoinduced H2-evolution occurs using Pfl as photosensitizer. Inhibition experiments and flow-dialysis measurements indicate that the effective H2-evolution originates from the association of Pfl to the ß-CD receptor sites.

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