Electrosynthesis and characterization of a donor–acceptor type electrochromic material from poly(4,7-dicarbazol-9-yl-2,1,3-benzothiadia-zole) and its application in electrochromic devices

Abstract

A donor–acceptor type monomer 4,7-dicarbazol-9-yl-2,1,3-benzothiadiazole (CBTD) was synthesized by modified Ullmann coupling reaction and its corresponding polymer (PCBTD) was obtained via electrochemical polymerization. Characterizations of the resulting polymer PCBTD were performed by cyclic voltammetry, UV–vis spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. The polymer displayed multiple colors changed from yellow to yellowish green, green, and turquoise blue with the applied potential. The UV–vis spectra depicted that polymer film have two absorption bands as expected for this type of donor–acceptor polymer, at 320 and 467nm, which attributed to the π–π* transition and intrachain charge transfer transition, respectively. Further, electrochemical and optical band gaps were obtained by using their oxidation and reduction onset potentials and absorption edges, respectively. The optical contrasts of the PCBTD film were found to be 28.1% at 420nm and 49.9% at 800nm in the visible region. The dual type electrochromic device constructed utilizing PCBTD and poly(3,4-ethylenedioxythiophene) showed a maximum contrast (ΔT %) of 49.4% at 620nm with response time of 0.6s and exhibited high coloration efficiency (1728cm2C−1) and good stability. These properties make the polymer a suitable material for electrochromic applications.