Design and synthesis of donor-acceptor electrochromic polymers with remarkable near-infrared modulation

Developing electrochromic polymers (ECPs) for application in smart windows is highly desirable in the electrochromic field. However, most ECPs present weak solar irradiance regulation due to the inverse visible and NIR modulation. Herein, three donor-acceptor polymers containing 4,7-bis(4-hexylthiophen-2-yl)benzo[c][1,2,5] thiadiazole (HT-TZ) units are synthesized via direct arylation polymerization (DArP) method, and two copolymers with similar structure are prepared by electrochemical copolymerization for comparison. The copolymers synthesized by the DArP method present weak visible and high NIR modulation with an average visible (380 nm-780 nm) contrast below 15 % and NIR (750 nm-1400 nm) contrast above 60 %, inducing a high solar heat gain coefficient (SHGC) difference above 0.2 between the neutral and oxidized states, which is much higher than the reported high-performance ECPs. Additionally, these synthesized copolymers also present good electrochromic properties such as good stability and normal coloration efficiency, confirming their broad application potential in smart windows.