Redox-controlled photosensitization of nanocrystalline titanium dioxide

Photosensitization of nanocrystalline titanium dioxide materials has been achieved by chemisorption of the pentacyanothiamine-ferrate(II) complex, which offers a relatively high redox potential that determines the photoelectrochemical properties of the photosensitized TiO2. The adsorbed pentacyanoferrate complex binds to TiO2 through the cyanide bridge and forms a new surface complex characterized by a metal-to-metal charge-transfer transition (MMCT) (Fe-II -> Ti-IV). The photosensitization can be observed only at low potentials at which FeII moieties are present. Photo-current switching between anodic and cathodic can be induced by varying either the photoelectrode potential or the wavelength of the incident light. Simple molecular modeling - together with spectroscopic and electrochemical measurements - allows the elucidation of the mechanism of the observed photoelectrochemical behavior.