Bias-Dependent Oxidative or Reductive Quenching of a Molecular Excited-State Assembly Bound to a Transparent Conductive Oxide

Visible light induced electron or hole injection by the surface-bound molecular assembly [(4,4'-(Me)(2)bpy)(4,4'-(CH2PO3H2)(2)bpy) - Ru-II(MebpyCH(2)CH(2)bpyMe)Re-I(CO)(3)Br](2+) (Me = CH3, bpy =2,2'-bipyridine) into In2O3:Sn nanopartides (nanoITO) has been investigated as a function of applied bias by transient absorption spectroscopy. The metallic properties of degenerately doped nanoITO allowed the driving force for electron or hole injection to be varied systematically by controlling the Fermi level of the oxide through an applied bias. At E-app > 0.4 V vs SCE, electron injection occurred by oxidative quenching of the Ru-based metal-to-ligand charge-transfer (MLCT) excited state to yield oxidized Ru-III. At E-app < 0.4 V, hole injection by reductive quenching of the MLCT excited state yielded reduced Ru-II(bpr(center dot-)) followed by rapid intra-assembly electron transfer to generate Re-I(bpr(center dot-)).