Modular Construction of Photoanodes with Covalently Bonded Ru- and Ir-Polypyridyl Visible Light Chromophores.

1,10-phenanthroline is grafted to indium tin oxide (ITO) and titanium dioxide nanoparticle (TiO) semiconductors by electroreduction of 5-diazo-1,10-phenanthroline in 0.1 M HSO. The lower and upper potential limits (-0.20 and 0.15 V, respectively) were set to avoid reduction and oxidation of the 1,10-phenanthroline (phen) covalently grafted at C5 to the semiconductor. The resulting semiconductor-phen ligand (ITO-phen or TiO-phen) was air stable, and was bonded to Ru- or Ir- by reaction with cis-[Ru(bpy)(CHCN)] (bpy = 2,2'-bipyridine) or cis-[Ir(ppy)(CHCN)] (ppy = ortho-C metalated 2-phenylpyridine) in CHCl and THF solvent at 50 °C. Cyclic voltammetry, X-ray photoelectron spectroscopy, solid-state UV-vis, and inductively coupled plasma-mass spectrometry all confirmed that the chromophores SC-[(phen)Ru(bpy)] and SC-[(phen)Ir(ppy)] (SC = ITO or TiO) formed in near quantitative yields by these reactions. The resulting photoanodes were active and relatively stable to photoelectrochemical oxidation of hydroquinone and triethylamine under neutral and basic conditions.