Electrochromic Organic-Metallic Hybrid Polymers: Fundamentals and Device Applications

Organic-metallic hybrid polymers are formed by the complexation of metal ions with organic ligands or polymers bearing coordination sites. Hybrid polymers consisting of bis(terpyridine)s and metal ions such as Fe(II) or Ru(II) have specific colors based on metal-to-ligand charge transfer (MLCT) absorption. The cyclic voltammograms of the polymers revealed a reversible redox wave that depends on the redox reaction of the metal ions. Interestingly, polymer films cast on indium tin oxide (ITO) electrodes have excellent electrochromic properties; the color of the film disappears when a potential higher than the redox potential of the metal ions is applied to the polymer film. Various colors such as purple, blue, red, and orange can be observed by changing the metal species and/or by modifying the organic ligands used to synthesize the polymers. In addition, multicolor electrochromic changes in a polymer film occur upon the introduction of two types of metal ions into the polymer. Electrochromic solid-state devices have been successfully fabricated by using these polymers.