Stabilization of a ruthenium(II) polypyridyl dye on nanocrystalline TiO2 by an electropolymerized overlayer

The long-term performance of dye-sensitized solar and photoelectrochemical cells is strongly dependent on the stability of surface-bound chromophores and chromophore-catalyst assemblies at metal oxide interfaces. We report here electropolymerization as a strategy for increasing interfacial stability and as a simple synthetic route for preparing spatially controlled, multicomponent films at an interface. We demonstrate that [Fe(v-tpy)2](2+) (v-tpy = 4'-vinyl-2,2':6',2″-terpyridine) can be reductively electropolymerized on nanocrystalline TiO2 functionalized with a phosphonate-derivatized Ru(II) polypyridyl chromophore. The outer:inner Fe:Ru ratio can be controlled by the number of reductive electrochemical scan cycles as shown by UV-visible absorption and energy dispersive X-ray spectroscopy measurements. Overlayer electropolymerization results in up to 30-fold enhancements in photostability compared to the surface-bound dye alone. Transient absorbance measurements have been used to demonstrate that photoexcitation and electron injection by the MLCT excited state(s) of the surface-bound Ru(II) complex is followed by directional, outside-to-inside, Fe(II) → Ru(III) electron transfer. This strategy is appealing in opening a new approach for synthesizing surface-stabilized chromophore-catalyst assemblies on nanocrystalline metal oxide films.