Synthesis of polyether-bridged bithiophenes and their electrochemical polymerization to electrochromic property

Abstract The polyether-bridged 2,2′-bithiophenes were designed with a single methylene between the thiophene ring and the first oxygen atom in polyether, and synthesized by the Williamson reaction and the Suzuki coupling reaction. The electrochemical polymerization of as-synthesized monomers were investigated. The as-prepared polymers of polyether-bridged 2,2′-bithiophenes (P(BT-E-BT)) show a better electrochemical activity with a high-quality film on electrodes compared to the polymers of polyether-bridged thiophenes (T-E-T) in a neutral media. The P(BT-E-BT) exhibited broad absorption in near infrared region with the band gaps (2.03–2.05 eV) and the good thermal stability. The versatile coloration change for P(BT-E-BT) films on a ITO glass electrode were achieved from salmon pink (neutral state) to blue–green and transmissive rusty red (oxidized states). Further electrochromic investigation implied that the polymer P(BT-E-BT) films showed moderate to high contrast ratios, good coloration efficiencies, low switching voltages, fast response times, excellent stabilities and colour persistence as potential electrochromic materials.