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

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 RuII(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.