LAUSR

Two ruthenium compounds were anchored to mesoporous nanocrystalline TiO2 thin films to probe local electric fields generated by TiO2 reduction or cation adsorption in acetonitrile electrolytes. The metal-to-ligand charge-transfer (MLCT) excited states were well formulated as [RuIII(dtb)2(dcb–)]2+* and [RuIII(btfmb)(dcb)(btfmb–)]2+*, where dtb is 4,4′-(tert-butyl)2-2,2-bipyridine, dcb is 4,4′-(CO2H)2-2,2-bipyridine, and btfmb is 4,4′-(CF3)2-2,2-bipyridine. The MLCT excited state was orientated toward the TiO2 surface linker (antiparallel to the field) for Ru(dtb)2(dcb–)*/TiO2 and away from the surface for Ru(btfmb)(dcb)(btfmb–)*/TiO2. Reduction of the TiO2 in an electrochemical cell resulted in a blue shift of the Ru(dtb)2(dcb–)*/TiO2 photoluminescence spectrum, while the Ru(btfmb)(dcb)(btfmb–)*/TiO2 spectrum was either unchanged or was red-shifted. Accompanying these spectral shifts were bimodal changes in the PL intensity and excited-state lifetime that first increased and then decreased as the quasi-Fer...