Organic soluble linear metallo-supramolecular polymer based on iron(II) and terpyridyl ligand with high electrochromic performance

Ionic metallo-supramolecular materials possess excellent electrochromic properties due to the coordination of organic ligands and inorganic metal ion. In this paper, we prepared a linear organic soluble metallo-supramolecular electrochromic material named P-FeTPY which was coordinated with terpyridine as organic ligands and Fe(II) as inorganic metal ion. The polymer P-FeTPY whose ligands were modified with alkyl chains could be dissolved in dichloromethane with a solubility of 20 g/L. This indicates the introduction of long alkyl chains is effective to increase solubility of the ionic metallo-supramolecular polymer. The polymer films were spin-coated on the ITO substrate and their electrochemical and electrochromic properties were investigated. P-FeTPY film showed purplish red color with an absorption band at around 580 nm in neutral state due to the metal-to-ligand charge transfer transition, and became colorless due to the oxidization of central metal ion with around 30% change in transmittance. Cyclic voltammetry test demonstrated that P-FeTPY film which showed a couple of redox peaks at 1.15 V and 0.95 V is electrochemically reversible and stable. After 240 switching cycles, 97% of the optical contrast was retained, indicating excellent stability of P-FeTPY film. This work provides an effective path for producing organic soluble ionic metallo-supramolecular materials, which is solution processible and will greatly benefit the large area production in future industrial applications.