Chemical approaches to artificial photosynthesis: A molecular, dye-sensitized photoanode for O₂ production prepared...

We describe here the preparation of a family of photoanodes for water oxidation that incorporate an electron acceptor-chromophore-catalyst in single molecular assemblies on nano-indium tin oxide (nanoITO) electrodes on fluorine-doped tin oxide (FTO). The assemblies were prepared by using a layer-by-layer, Atomic Layer Deposition (ALD), self-assembly approach. In the procedure, addition of an electron acceptor viologen derivative followed by a Ru^II(bpy) chromophore and a pyridyl derivative of the water oxidation catalyst [Ru(bda) (L)₂] (bda = 2,2'-bipyridine-6,6'-dicarboxylate)₂, were linked by ALD by addition of the bridge precursors TiO₂, ZrO₂, and Al₂O₃ as the bridging groups giving the assemblies, FTO|nanoITO|-MV²⁺-ALD MO₂-RuP₂ ²⁺-ALD M'O₂-WOC. In a series of devices, the most efficient gave water oxidation with an incident photon to current efficiency of 2.2% at 440 nm. Transient nanosecond absorption measurements on the assemblies demonstrated that the slow step in the intra-assembly electron transfer is the electron transfer from the chromophore through the viologen bridge to the nanoITO electrode.