Synthesis and characterization of a novel multicolored electrochromic polymer based on a vinylene-linked EDOT-carbazole monomer

A novel heterocycle-based monomer (BEDOT-V-NEtCz) is designed and synthesized using 3,4-ethylenedioxythiophene (EDOT) as the end units and 3,6-linked N-ethyl-carbazole (NEtCz) as the inner unit spaced by vinylene (V). The monomer BEDOT-V-NEtCz can be electrochemically oxidized at a very low onset potential of 0.41V vs SCE. The resulting electroactive polymer (PBEDOT-V-NEtCz) is electrochemically synthesized by cyclic voltammetry (CV) method and its electrochromic properties are reported. Characterizations of PBEDOT-V-NEtCz film are performed by CV, scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). Spectroelectrochemical analysis reveals that PBEDOT-V-NEtCz film shows multicolored electrochromism: brick-red in the reduced state, sky-blue in the oxidized state and three intermediate colors (brown at 0.2V, olive green at 0.4V and blue-green at 0.6V vs SCE). The color changes are accompanied by good optical contrasts of 50% at 759nm and 27% at 470nm, respectively. Kinetic studies reveal that the switching time of PBEDOT-V-NEtCz film are 1.2s (759nm) and 1.9s (470nm) for the bleaching process and 1.4s (759nm) and 1.8s (470nm) for the coloration process (95% of the full ΔT%), respectively. The resultant polymer could be useful as the active layers in electrochromic devices.