Dye Excited States Oriented Relative to TiO2 Surface Electric Fields

作者：Ward Cassandra L; DiMarco Brian N; O'Donnell Ryan M; Meyer Gerald J^*

来源：Journal of Physical Chemistry C, 2018, 122(25): 13863-13871.

DOI：10.1021/acs.jpcc.8b01010

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 [Ru-III(dtb)(2)(dcb(-))](2+)* and [Ru-III(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-Fermi level of the TiO2 thin films was raised toward the vacuum level with a potentiostat. The initial increase was coincident with a lower excited state injection yield, while the origin(s) of the decrease observed at more negative applied potentials remains speculative. The potential dependence and magnitude of the spectral shifts and intensity/lifetime changes were acutely sensitive to the identity of the cations present in the acetonitrile electrolytes.

• 出版日期2018-6-28