A fast switching, low band gap, p- and n-dopable, donor–acceptor type polymer

A new electrochromic polymer, poly(2,3-diphenyl-5,7-bis(3,4-ethylenedioxy-2-thienyl)thieno[3,4-b]pyrazine) (PGS) is electrochemically synthesized and its electrochromic properties are reported. PGS showed well defined electrochemical characteristics with a relatively low oxidation potential of 0.18 V vs Ag/Ag+. Polymer also exhibited a definite redox couple at applied cathodic potentials, indicating n-doping characteristic of the polymer. Spectroelectrochemistry and previously unattempted technique, ESR data was utilized to confirm the existence of dual type π–π∗ transitions centered at 522 nm and 1062 nm. The polymer exhibits multi-color electrochromism where three distinct colors are achievable by varying the redox state of the polymer between saturated red-purple color, blue and colorless-gray in neutral, n- and p-doped states, respectively. Copolymerization as a facile method to tune the electrochromic properties of the material was also realized in the presence of 2,2′-bis(3,4-ethylenedioxythiophene) (BiEDOT). Both polymers exhibit very short switching time (0.4 s) and express more than 45% change in the transmittance in the near-IR region, which could make these polymers useful in applications in NIR electrochromic devices.