Two random copolymers, poly (benzotriazole-indacenodithiophene-benzothiadiazole) (PBTIDBD) and poly (benzotriazole-benzodithiophene-benzothiadiazole) (PBTBDBD) were synthesized and characterized by electrochemistry, spectroelectrochemistry, electrochromic switching, colorimetry and thermal gravimetric analysis. For PBTIDBD, the color of film changed from rosybrown in neutral state to transparent lightgrey in oxidized state. The band gap calculated according to the spectroelectrochemistry data is 1.86 eV, and the response time, optical contrast, coloration efficiency at 1560 nm are 1.04 s, 62.1%, 276.29 cm 2 ∙C -1 , respectively. And, for PBTBDBD, its color changes from rosybrown to transparent grey as it was fully oxidized. The band gap is 1.68 eV, and the response time, optical contrast, coloration efficiency at 1560 nm are 2.68 s, 62.4%, 193.31 cm 2 ∙C -1 , respectively. Both copolymers are stable at a high temperature, and the decomposition temperature of PBTIDBD and PBTBDBD are 463 °C and 326 °C. Both copolymers can be good candidates for electrochromic application.
The synthesis of high-performance electrochromic polymers remains a key research highlight in the field of electrochromism. Herein, a series of donor-acceptor type conjugated polymers are synthesized based on 4,9-Dihydro-s-indaceno[1,2-b:5,6-b]dithiophene (IDT), 3,4-ethylenedioxythiophene (EDOT), benzo[c][1,2,5]thiadiazole (BTD) and benzothiadiazo-[3,4-g]-quinoxaline (TQX) units by Stille coupling polymerization. By fine-tuning the ratios between the monomers, the synthesized copolymers exhibited diverse color options and tunable properties, by applying an extra potential, polymer films transit from yellow, pink, green, and dark brown to highly transmissive state, along with outstanding electrochromic properties in both the NIR region and the visible region, such as high optical contrast, rapid switching response, and excellent stability. As a result, the derived electrochromic devices demonstrate an optical contrast exceeding 40 % and retained over 74 % of their optical contrast after 1000 switching cycles. These findings collectively demonstrate that these copolymers hold significant potential for applications in smart windows and adaptive camouflage as a versatile color palette.
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