Reductive electropolymerization of bis-tridentate ruthenium complexes with 5,5′′-divinyl-4′-tolyl-2,2′:6′,2′′-terpyridine

Abstract

Four bis-tridentate ruthenium complexes with 5,5′′-divinyl-4′-tolyl-2,2′:6′,2′′-terpyridine (dvtpy) have been synthesized. Among them, 3(PF₆) ([(dvtpy)Ru(Mebib)](PF₆)) and 4(PF₆) ([(dvtpy)Ru(dpb)](PF₆)) are cyclometalated, and 5(PF₆)₂ ([(dvtpy)Ru(Mebip)](PF₆)₂) and 6(PF₆)₂ ([(dvtpy)Ru(tpy)](PF₆)₂) are noncyclometalated, where Mebib is 2-deprotonated-1,3-bis(N-methylbenzimidazolyl)benzene, dpb is 2-deprotonated-1,3-di(2-pyridyl)benzene, Mebip is 2,6-bis(N-methylbenzimidazolyl)pyridine, and tpy is 2,2′:6′,2′′-terpyridine, respectively. Reductive electropolymerization of these complexes and copolymerization of 4(PF₆) and 5(PF₆)₂ proceeded smoothly, both on glassy carbon and ITO glass electrodes, to afford stable metallopolymeric films with well-defined redox processes. On the basis of the monomer structures, electrochemical properties, and polymerization mechanism, the polymer chains of these materials are supposed to be composed of organic frameworks with the metal ions laterally chelated to the main backbones. The polymeric films on ITO surfaces display promising electrochromism in the visible region with good reversibility and moderate contrast ratio. Besides, the apparent diffusion constants of films of 3(PF₆)–6(PF₆)₂ were measured by potential step chronoamperometry and the typical surface morphology of poly-5(PF₆)₂/ITO film was studied using SEM.