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-Ru-III(NH3)(4)pyCOOH [pyCOOH = isonicotinic acid; M = cis-Ru(bpy)(2)(CN)(2), 1 (bpy = 2,2' 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.