Novel Ru-dioxolene complexes as potential electrochromic materials and NIR dyes

A series of Ru(bpy)(2)-dioxolene complexes 1-4 (bpy = 2,2'-bipyridine) and corresponding Ru(dcb)(2)-dioxolene complexes 5-8 (dcbH(2) = 2,2'-bipyridine-4,4'-dicarboxylic acid) have been prepared, and their spectroelectrochemical behavior in solution has been investigated. The complexes show reversible electrochemical behavior accompanied by a strong NIR absorption in their semiquinone forms due to a Ru(dpi) --> sq(pi*) MLCT band. Complete quenching of the NIR absorption occurs both upon oxidation (to the quinone form) and upon reduction (to the catechol form) very close to 0 V. The color of the systems can be tuned by using a wide range of ligands. The complexes 5-8 can be anchored onto nanocrystalline inorganic semiconductors allowing incorporation into potential electrochromic devices. As a proof of principle, compound 8 has been adsorbed on nanocrystalline Sb-doped SnO2 supported on FTO glass, and it displays reversibly switchable electrochromic behavior in the NIR.