Synthesis, characterization, and electrochromic properties of conducting copolymers of 2-[(3-thienylcarbonyl)oxy]ethyl 3-thiophene carboxylate with thiophene and pyrrole

2-[(3-Thienylcarbonyl)oxy]ethyl 3-thiophene carboxylate (TOET) was synthesized via the reaction of 3-thionylcarboxylic acid with ethylene glycol, and electrochemically polymerized with thiophene (Th) and pyrrole (Py) by using tetrabutylannnonium tetrafluoroborate (TBAFB) as the supporting electrolyte in acetonitrile (ACN). Characterization of the resulting copolymers were performed via cyclic voltammetry, FTIR, and scanning electron microscopy (SEM). Electrical conductivities are measured by the four-probe technique. Spectroelectrochemical analysis shows that the copolymer of this monomer with Th has an electronic band gap (due to the pi-pi* transition) of 1.97 eV. The homopolymer possessed a yellow color in its reduced form, and a greenish blue color in its oxidized form, however, no switching ability. The copolymer exhibited multi-color changes from a pale red in the neutral state, an orange, and finally a bluish-gray upon oxidation, and a long-term switching stability up to 450 double switches.