Ashford, Dennis L., Song, Wenjing, Concepcion, Javier J., Glasson, Christopher R.K., Brennaman, M. Kyle, Norris, Michael R. , Fang, Zhen, Templeton, Joseph L., and Meyer, Thomas J. (2012) Photoinduced electron transfer in a chromophore−catalyst assembly anchored to TiO2. Journal of the American Chemical Society, 134 (46). pp. 19189-19198.

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Abstract

Photoinduced formation, separation, and buildup of multiple redox equivalents are an integral part of cycles for producing solar fuels in dye-sensitized photoelectrosynthesis cells (DSPECs). Excitation wavelength-dependent electron injection, intra-assembly electron transfer, and pH-dependent back electron transfer on TiO2 were investigated for the molecular assembly [((PO3H2-CH2)-bpy)2Rua(bpy-NH-CO-trpy)Rub(bpy)(OH2)]4+ ([TiO2–RuaII–RubII–OH2]4+; ((PO3H2-CH2)2-bpy = ([2,2'-bipyridine]-4,4'-diylbis(methylene))diphosphonic acid); bpy-ph-NH-CO-trpy = 4-([2,2':6',2"-terpyridin]-4'-yl)-N-((4'-methyl-[2,2'-bipyridin]-4-yl)methyl) benzamide); bpy = 2,2'-bipyridine). This assembly combines a light-harvesting chromophore and a water oxidation catalyst linked by a synthetically flexible saturated bridge designed to enable long-lived charge-separated states. Following excitation of the chromophore, rapid electron injection into TiO2 and intra-assembly electron transfer occur on the subnanosecond time scale followed by microsecond–millisecond back electron transfer from the semiconductor to the oxidized catalyst, [TiO2(e–)–RuaII–RubIII–OH2]4+→[TiO2–RuaII–RubII–OH2]4+.

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