Assembly of Molecular Chromophore–Catalyst Assemblies on Metal Oxide Semiconductors by Metal–Ligand Coordination Chemistry

Chromophore–catalyst assemblies were synthesized on high surface area metal oxide surfaces by self-assembly, taking advantage of coordinate covalent bonding interactions. Phosphonic acid/phosphonate derivatized ruthenium(II) polypyridyl complexes are shown to be capable of acting as ligands for a dinuclear cobalt complex as well as serving to anchor the ruthenium(II) polypyridyl species on metal oxide substrates. The relative surface concentrations of the species can be controlled via the protonation state of the phosphonic acid functional groups. This strategy enables the formation of complex molecular architectures by the formation of coordinate covalent bonds to join synthetically accessible components. The resulting functional assemblies on semiconductor substrates offer spatial control over the relative positions of electron transfer partners for photoinduced electron transfer reactivity. These assemblies have been investigated spectroscopically and electrochemically; their electron transfer dynamics following photoexcitation have been investigated by optical transient absorption spectroscopy, and their activity as photoanodes has been investigated.