Benzotriazole-based donor-acceptor type low band gap polymers with a siloxane-terminated side-chain for electrochromic applications

Abstract

A series of donor–acceptor (D-A) type polymers (P1-P4) bearing a benzotriazole group with a siloxane terminated side-chain and a long alkyl chain were synthesized via Stille coupling, and the electrochromic (EC) properties were characterized by various analytical techniques. The incorporation of hybrid siloxane-solubilizing groups in P1 and P2 influenced the intermolecular interactions among the adjacent polymer chains and increased the solubility of the resulting polymers in common organic solvents. The EC behavior of the polymers revealed a color transition from red to blue upon oxidation and reduction. In particular, P1, containing a short siloxane-terminated side-chain, showed superior optical performances, with transmittance change of 42.7%, the change in optical density of 0.767, and coloration efficiency of up to 327 cm2/C, and exhibited superior operational stability, with little transmittance changes after 100 potential steps. Overall, these properties highlight the potential applications of current polymers in displays and smart windows.