Synthesis and Properties of a Novel Electrochromic Polymer Obtained from the Electropolymerization of a 9,9'-Spirobifluorene-Bridged Donor−Acceptor (D−A) Bichromophore System

The synthesis and photophysical, electrochemical, and spectroelectrochemical characterization of a novel donor−acceptor (D−A) bichromophore system composed of two D−A segments linking through a spiro center are reported. The electron-donating (D) moieties are triphenylamine (TPA) groups, whereas the electron-withdrawing (A) moieties are cyano groups. The particular “spiro” configuration that perpendicularly bonds the D−A chromophores by a tetrahedral carbon, impedes orbital interactions between the branches. Thus, the two TPA substituents act independently, rendering an efficient electropolymerization process feasible. The polymer film obtained showed reversible electrochemical oxidation accompanied by strong color changes with high coloration efficiency and contrast ratio, which can be switched by potential modulation. The remarkable electrochromic behavior of the film is clearly interpreted on the basis of spectroelectrochemical studies. A plausible polymerization mechanism involved with the TPA dimerization reaction is proposed for the electropolymerization process.