Electrochromic behaviors of novel conjugated copolymers based on [1,2,5]thiadiazolo[3,4-g]quinoxaline, carbazole and cyclopentadithiophene units: Multicolor, double-doping and low band gap

Abstract

A new kind of random ternary D-A type conjugated copolymers were designed employing [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) units as the acceptor, carbazole and cyclopentadithiophene units as the donors. In the experiments, two polymers named PTCD-1 and PTCD-2 were obtained by changing feed ratios of the three units. It was found that the two polymers possessed double-doping feature, and they exhibited multiple color changes of yellow/green/transparent gray in the p-type doping process and single color changes of yellow/red in the n-type doping process. In the electrochromic switching, PTCD-1 and PTCD-2 displayed low optical band gaps as 1.29 eV and 1.27 eV, respectively. They also presented favorable solubility, kinetic properties and thermal stability. In particular, both polymers had short response time (lowest as 0.18 s) and high coloring efficiency (up to 657.1 cm 2 C −1 ). The favorable electrochromic behaviors especially the multicolor and double-doping properties made the two polymers worth in-depth attention and investigation. • Two D-A type copolymers containing thiadiazoloquinoxaline, carbazole and cyclopentadithiophene units were synthesized. • The polymers displayed multichromism and double-doping feature. • The polymers showed desirable electrochromic properties with low band gaps.