Efficient blue-to-transmissive electrochromic transitions of alkylated quinoxaline-thiophene based donor-acceptor type conjugated polymers

Abstract

Two electrochromic copolymers, P1 and P2, were synthesized from Stille coupling reactions of dibrominated phenazine having branched and linear alkyl side-chains, respectively, with distannyl thiophene. The prepared donor–acceptor type electrochromic polymers showed good solution processability, superior switching characteristics, and high redox stability. In electrochromic measurements, the polymers exhibited reversible blue-to-transmissive switching at an applied voltage of 0.9 V and 1.2 V, respectively, with transmittance changes of 18.1% at 597 nm and 25.3% at 653 nm for P1 and P2, respectively. They showed high coloration efficiencies of 232.5 and 132.6 cm2/C, respectively, in the visible region and long-term stability for more than a hundred cycles. Furthermore, the polymers were completely transparent in the bleached state, accompanied by high NIR absorption, upon oxidation. These results manifest that the alkyl side-chains on the quinoxaline acceptor unit could dictate the intermolecular interactions of polymer chains affecting the electrochromic performances. The findings of this study suggest the strategy of designing and preparing efficient electrochromic polymers with selective absorption in long visible and NIR regions for smart windows and displays.