Copolymerization of Azobenzene-bearing Monomer and 3,4-Ethylenedioxythiophene (EDOT): Improved Electrochemical Performance for Electrochromic Device Applications

In this study, novel electrochromic copolymers of 3,4-ethylenedioxythiophene (EDOT) and (E)-1,2-bis(2-fluoro-4-(4-hexylthiophen-2-yl)phenyl)diazene (M1) with different monomer feed ratios were designed and synthesized electrochemically. Electrochemical and spectroelectrochemical characterizations were performed using voltammetry and UV-Vis-NIR spectrophotometry techniques to test the applicability of copolymers for electrochromic applications. In terms of electrochemical behaviors, addition of an electron-rich EDOT unit into the azobenzene-containing copolymer increased the electron density on the polymer chain and afforded copolymers with very low oxidation potentials at around 0.30 V. While the homopolymers (P1 and PEDOT) exhibited neutral state absorptions centered at 510 and 583 nm, EDOT-bearing copolymers showed red shifted absorptions compared to those of P1 with narrower optical band gaps. In addition, the poor optical contrast and switching times of azobenzene-bearing homopolymer were significantly improved with EDOT addition into the copolymer chain. As a result of the promising electrochromic and kinetic preperties, CoP1.5-bearing single layer electrochromic device that works between purple and light greenish blue colors was constructed and characterized.