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 (TiO2) semiconductors by electroreduction of 5-diazo-1,10-phenanthroline in 0.1 M H2SO4. The lower and upper potential limits (−0.20 and 0.15 VSCE, 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 TiO2-phen) was air stable, and was bonded to Ru- or Ir- by reaction with cis-[Ru(bpy)2(CH3CN)2]2+ (bpy = 2,2′-bipyridine) or cis-[Ir(ppy)2(CH3CN)2]+ (ppy = ortho-Cphenyl metalated 2-phenylpyridine) in CH2Cl2 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)2]2+ and SC-[(phen)Ir(ppy)2]+ (SC = ITO or TiO2) formed in near quantitative yields by these reactions. The resulting photoanodes were active and relatively stable to photoelectroch...