Multi-electrochromic 2,7-linked Polycarbazole Derivative and Its Application in Electrochromic Devices

Two 2,7-linked carbazole derivatives, 2,7-bis(2-thiophene)-N-methylcarbazole (BTC) and 2,7-bis(2-3,4-ethylenedioxythiophene)-N-methylcarbazole (BEC), were successfully synthesized and electropolymerized. The electrochemical and optical investigations indicated that the two monomers and their resulting polymers (PBTC and PBEC) showed excellent polymerization and redox activity, and substitution with EDOT units resulted in a decrease in the monomer and polymer oxidation potentials, narrowing of the electronic band gap relative to the corresponding thiophene substituted 2,7-carbazoles. Spectroelectrochemical study revealed that both of the polymers had interesting electrochromic properties and displayed multi-electrochromic behaviors as well as good switching properties. The electrochromic properties of the two polymers are dependent on the selective of substituents attached at the 2,7-positions of N-methylcarbazole. Moreover, dual-type electrochromic devices (ECDs) consisting of PBTC (or PBEC) and PEDOT layers were also fabricated and characterized in detail. It was found that both of the ECDs dispalyed good electrochromic performances, such as reasonable optical contrast, fast response time and excellent redox stability