Electrochromic films with high optical contrast prepared by oxidative electropolymerization of a novel multi-functionalized cyclometalating ligand and its neutral-charged Pt(II) complexes

A novel multi-functionalized cyclometalating ligand (HL) and its two neutral-charged Pt(II) complexes, i.e., [(L)PtCl] (C1) and [(L)Pt(CCC6H5)] (C2) (HL = 4-{p-[N-(4-(9-carbazole))butyl-N-phenyl]anilino}-6-phenyl-2,2′-bipyridine), have been successfully synthesized and verified by 1H NMR, 13C NMR, elemental analysis and/or X-ray crystallography. The introduction of the electron-donating arylamino unit at the 4-position of the electron-withdrawing 6-phenyl-2,2′-bipyridine ligand forms the D–A system, resulting in the enhanced 1MLCT bands in the absorption spectra and intense orange emissions in the PL spectra of C1 and C2. The carbazole units grafted through alkyl chain in HL, C1 and C2 electrochemically trigger the efficient cross-linking reaction to form polymer films, which have been characterized by AC impedance, SEM and spectroelectrochemistry. Each of the poly-HL and poly-C1 films exhibits reversible oxidation with significant color change having a high contrast ratio (81.8% for poly-HL film and 67.3% for poly-C1 film), a reasonable coloration response time (6.3 s for poly-HL film and 3.1 s for poly-C1 film) and a comparable coloration efficiency (158 C−1 cm2 for poly-HL film and 132 C−1 cm2 for poly-C1 film) that can be switched by modulation of the applied potential.

Anodic coloration materials: The arylamine modified (C^N^N) ligand with a grafting carbazole moiety through alkyl chain and its cyclometalated Pt(II) complexes have been electrochemically deposited on Pt or ITO electrode to form orange polymer films, which show the anodic coloration effect with high optical contrast.Figure optionsDownload as PowerPoint slideHighlights
► D–A system between the electron-donating arylamine group and the electron-deficient (C^N^N) moiety.
► Carbazole unit grafted through alkyl chain triggers the electropolymerization process.
► Multi-redox behavior in the well-adhered metallopolymer film.
► Anodic coloration materials with high contrast ratio, reasonable coloration response time and comparable coloration efficiency.