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

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.