Slow cation transfer follows sensitizer regeneration at anatase TiO2 interfaces

After rapid photoinduced electron injection into TiO(2) and regeneration by a donor, D, such as iodide or phenothiazine, sensitizers are present in an environment distinctly different from that prior to light absorption. Significantly, the absorption spectrum of the Ru(II) sensitizer in this new environment is one that is known to be less favorable for excited-state electron injection. The transient absorption features were found to report on photoinduced variations in the local electronic environment of the Ru(II) sensitizer-TiO(2) interface that were induced by ion transfer. The data demonstrate that slow (mu s to ms) cation transfer follows regeneration to yield the sensitizer that was initially photoexcited.