Effects on the electrochemical and electrochromic properties of 3,6 linked polycarbazole derivative by the introduction of different acceptor groups and copolymerization

• ETCB and NDTC were synthesized. And their polymers were obtained by electropolymerization.
• Both the polymer films showed well-defined oxidation and reduction process.
• The PETCB and PNDTC films showed reasonable optical contrast and two colors under different potentials.
• The copolymer film based on ETCB and EDOT could display five colors and higher optical contrast.

Two novel donor–acceptor type monomers, ethyl 4-(3,6-di(thiophen-2-yl)-9H-carbazole-9-yl)-benzoate (ETCB) and 9-(4-nitrophenyl)-3,6-di(thiophen-2-yl)-9H-carbazole (NDTC), were synthesized and characterized. Both the monomers show good electrochemical activity. UV–vis absorption studies reveal that the spectra of them are obviously different due to the introduction of the acceptor groups with different polarity, and the compound with –NO2 group has lower band gap. Fluorescent spectral studies indicate that the solution of ETCB in DCM exhibits sky-blue emission, while the NDTC hardly displays the fluorescence because of stronger intramolecular charge transfer. Their polymers can be synthesized by electropolymerization, and both the films show well-defined oxidation and reduction process. Spectroelectrochemical analysis reveals that PETCB film displays the color change from yellow–green (neutral) to blue–purple (oxidized), while the color change of PNDTC film is from yellow (neutral) to gray (oxidized). Both the polymer films exhibit reasonable optical contrast and switching time. Moreover, the copolymer based on ETCB and 3,4-ethylenedioxythiophene (EDOT) is also investigated. The copolymer could show five colors change under different applied potentials and higher optical contrast (50% of 1100 nm) and coloration efficiency (356.88 cm2 C−1).

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