Electrosynthesises and characterizations of copolymers based on thiophene and 3,4-ethylenedioxythiophene in boron trifluoride diethyl etherate

Copolymers based on thiophene and 3,4-ethylenedioxythiophene (EDOT) are successfully electrodeposited on ITO electrodes in boron trifluoride diethyl etherate (BFEE). Cyclic voltammograms (CVs), Fourier transition infrared spectra (FTIR), Scanning electron microscopy (SEM), and spectroelectrochemical analysis are used to characterize the structure and properties of the resultant copolymers. Spectroelectrochemistry indicates that electrochromic properties of the copolymer films can be tuned by controlling the feed ratio of thiophene/EDOT. The copolymer prepared with thiophene/EDOT feed ratio at 2/1 presents a more negative π–π* transition at 469 nm in comparison with the homopolymers and the bandgap is calculated as 1.80 eV by the onset wavelength. Furthermore, multicolor electrochromism (brown, yellow brown, gray yellow, and gray blue) can be achieved by this copolymer. The copolymer film shows optical contrast of 29% at 767 nm with a response time of 2.6 s and reasonable electrochemical stability, which retains 77.8% of its original electroactivity after 1000 cycles.

► Copolymers based on thiophene and EDOT are successfully prepared in BFEE solution.
► The electrochromic properties of the copolymer films can be tuned by controlling the feed ratio of thiophene/EDOT.
► The copolymer film prepared with the feed ratio of thiophene/EDOT at 2/1 exhibits four color electrochromism.
► The copolymer film presents reasonable switching response, open circuit memory and electrochemical stability.