Electrochemical preparation of donor-acceptor type conjugated polymer films: Effect of substitute units on electrochromic performance

Conjugated polymers exhibiting adjustable color changes under an electric field have been receiving great research interest due to their potential use in electrochromic applications. High-performance electrochromic materials are required to have well-defined donor-acceptor (D-A) units, a low optical bandgap, and fast response time. To fulfill these demands, herein, for the first time, two conducting macromolecules poly-3,8-diaminobenzo [c]cinnoline (P1) and poly-4,7-bis(phenyldiazenyl)benzo[c]cinnoline-3,8-diamine (P2) were successfully fabricated on the ITO substrate via electrochemical polymerization from their corresponding monomers in 0.1 M TBAP/acetonitrile solution. Consequently, two conjugated polymeric films show well-defined azo and amine functional groups, which are responsible for electron-withdrawing and electron-donating, respectively. The optical bandgaps (E-g) of P1 and P2 films were found 1.87 eV and 1.81 eV, respectively. The P1 exhibited a yellowish-brown color in neutral states and reduced states and a dark brown color in oxidized states while the P2 showed an orange color in neutral states, brownish orange color in oxidized states and a dark brown color in reduced states. It has been found that the P1 shows a higher conductivity, shorter switching time and better stability while P2 exhibits advanced the chromic and electron-withdrawing characteristics, which were attributed to the substituted phenyldiazenyl units contacted to the benzo[c]cinnoline (BCC) and lower oxidation potential of P2. This study opens a new avenue into the electrochromic application via the effective electropolymerization of corresponding monomers.