Novel Thiadiazolobenzotriazole Based Donor–Acceptor Type Conjugated Polymers as Neutral Green Electrochromic Materials

Thiadiazolobenzotriazole (TBZ)-containing donor-acceptor (D–A) type polymers are rarely investigated as electrochromic materials, although they have made important progress in the fields of organic transistors and solar cells. In this work, a new class of soluble D–A type electrochromic polymer is designed using the alkyl substituted TBZ units as the acceptor, the alkyl substituted 3,4-propylenedioxythiophene (ProDOT) units as the donor, and benzene (B) units as the π -bridge. Through altering the molar ratio of ProDOT/B/TBZ, three polymers named PPBT-1, PPBT-2 and PPBT-3 are chemically synthesized. After various characterizations, it is found that all the polymers display saturated green in their neutral states and switch to transparent gray upon oxidation with narrow optical bandgaps, and moreover, they demonstrate high optical contrast, rapid switching speed, and excellent coloration efficiency particularly in the near infrared region. The impacts of different donor-acceptor feed ratios on electrochromic performances are mainly reflected in the optical, electrochemical and kinetic properties. In contrast to PPBT-1 and PPBT-3, PPBT-2 show the best performances with the most appropriate ProDOT/B/TBZ ratio of 2/3/1 in its backbone. These positive results provide a theoretical basis for the research of electrochromic polymers based on TBZ units.