Hetero-Supramolecular Modification of Nanocrystalline TiO₂-Film Electrodes: Photoassisted Electrocatalysis at B₁₂-on-TiO₂

Nanocrystalline TiO2-film electrodes exhibit a unique set of intrinsic properties (transparency for visible light, electric conductivity in the doped state, semiconductor properties, large surface area, surface affinity towards organic anchoring groups). These can be combined with those of TiO2-surface-anchored molecular subunits such as light emitters or absorbers, redoxactive–possibly electrochromic–compounds, and electroactive molecular hosts or catalysts. The number of macroscopic devices resulting from such a hetero-supramolecular architecture includes photovoltaic cells, erasable photochromic devices, electrochromic displays and filters, and electrocatalytically active surfaces. The principals behind these applications are reviewed with special emphasis on a new type of photo assisted electrocatalysis using vitamin B12-modified TiO2.