Donor-Acceptor-Type Copolymers Based on 3,4-Propylenedioxy-thiophene and 5,6-Difluorobenzotriazole: Synthesis and Electrochromic Properties.

Three solution-processable D-A-type conjugated polymers P1, P2 and P3 were successfully synthesized via the Pd-catalyzed Stille cross-coupling copolymerization approach, with 6,8-Dibromo-3,3-bis-decyl-3,4-dihydro-2H-thieno[3,4-b][1,4] dioxepine (M1) and 2,5-Bis(trimethylstannanyl)thiophene (M3) as the donor units and 4,7-Dibromo-5,6-difluoro-2-(2-hexyl-decyl)-2H-benzotriazole (M2) as the acceptor unit, wherein the feed ratio of the three units was 1:3:4 (M1:M2:M3, the same below), 1:1:2 and 3:1:4 for P1, P2, and P3, respectively. The results obtained by our test showed that the feed ratio between the D and A units had a significant effect on both the electrochemical and the spectroelectrochemical properties of the three polymers. The copolymers exhibited a gradually deepening red color in neutral state with the increase of M1 content and then turned to a transmissive grey color in the oxidation state. Also, three copolymers showed good performance in electrochromic parameters, which mainly consists of optical contrast, response time, and coloration efficiency. In general, the excellent electrochromic performances of the copolymers make them outstanding candidates for electrochromic material applications.