Molecular rectification by a bimetallic Ru-Os compound anchored to nanocrystalline TiO2

The coordination compound [Ru(dcb)(2)(Cl)-bpa-Os(bpy)(2)(Cl)](PF6)(2), abbr eviated Ru-bpa-Os, where dcb is 4,4'-(COOH)(2)-2,2'-bipyridine and bpa is 1 ,2-bis(4-pyridyl)ethane, was anchored to nanocrystalline (anatase) TiO2 fil ms for interfacial electron transfer studies. Blue or green light excitatio n results in the sequence of electron transfer events shown schematically w here the Ru chromopihore injects an electron into the semiconductor, step 1 , and the Os(II) center reduces Ru(III), step 2, to farm an interfacial cha rge-separated state abbreviated TiO2(e(-))\Ru-bpa-Os(III). This same charge -separated state, TiO2(e(-))\Ru-bpa-Os(III), can be formed by a novel remot e electron injection process from the Os chromophore to the semiconductor s olid. The electron injection rates into the semiconductor are at least 5 or ders of magnitude faster than charge recombination. This is the first examp le of a bimetallic coordination compound that rectifies charge at a semicon ductor interface.