Electrochromic Devices Based on Binuclear Mixed Valence Compounds Adsorbed on Nanocrystalline Semiconductors

A series of cyano-bridged binuclear mixed valence complexes of the general formula M-RuIII(NH3)4pyCOOH [pyCOOH = isonicotinic acid; M = cis-Ru (bpy)2(CN)2, 1 (bpy = 2,2ʹ bipyridine); trans-Ru(py)4(CN)2, 2 (py = pyridine); [Ru(CN)6]^4-, 3; [Fe(CN)6]^4-, 4] have been prepared and anchored through the carboxylic function to nanocrystalline TiO2 or SnO2 electrodes. The complexes display a reversible electrochromic behavior in the range of applied potential from -0.5 to +0.5 V, versus SCE. Tuning of the electronic transitions in the visible and near-infrared spectral regions is achieved through changes of the solvent and of the cyano-bridged metal moiety M.