Novel Ru-Dioxolene Complexes as Potential Electrochromic Materials and NIR Dyes

A series of Ru(bpy)2-dioxolene complexes 1-4 (bpy = 2,2ʹ- bipyridine) and corresponding Ru(dcb)2-dioxolene complexes 5-8 (dcbH2 = 2,2ʹ-bipyridine4,4ʹ-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(d(pi)) (right arrow) 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.