Direct Observation of Photodriven Intermolecular Hole Transfer across TiO_2 Nanocrystallites: Lateral Self-Exchange Reactions and Catalyst Oxidation

摘要

Photoselection of Ru(Ⅱ)-polypyridyl sensitizers with polarized pulsed-light excitation, when anchored to TiO_2 nanocrystallites interconnected in a mesoporous thin film, results in an anisotropic distribution of excited sensitizers. Under conditions where excited-state sensitizers efficiently inject electrons into TiO_2 , the resulting oxidized sensitizers exhibit an initial anisotropy in their absorption difference spectra. Over the course of the charge-separated lifetime for many sensitizers, the transient absorption anisotropy signal decays to nearly zero indicative of lateral self-exchange hole-transfer reactions at the interface. When a cobalt metalloporphyrin catalyst was coanchored to the sensitized nanocrystalline TiO_2 film, excited-state injection was followed by lateral hole transfer to oxidize the surface-bound catalyst.