Single- and dual-type electrochromic devices based on polycarbazole derivative bearing pendent viologen

In relation to electrochromic (EC) device performance, it is important to avoid unwanted power consumption and to minimize electrochemical degradation by using an EC material, which exhibits the desired EC state under no bias voltage in most of the time. Regarding this point, we prepared single- and dual-type EC devices based on poly(N-methyl-N′-(6-carbazole-1-ylhexyl)-4,4′-bipyridinium dihexafluorophosphate) [P(Cz-V)]. Since polycarbazole is oxidative-coloring and viologen is reductive-coloring, the supplementary EC action provides variety in color, which cannot be achieved by individual EC materials. In the single-type device, the polymer became green P(Czα+-V2+) at 3 V (versus ITO), bleached P(Cz0-V2+) at 0 V, and violet P(Cz0-V+) at −3 V. In the dual-type device, the complementary action of (Czα+-V2+) and P(Cz0-V+) upon a bias voltage of 3 V showed higher EC contrast compared to the single-type device.