Synthesis, characterization and electrochromic properties of copolymer of terephthalic acid bis-(thiophen-3-yl-methyl) thioester with thiophene

Terephthalic acid bis-(thiophen-3-yl-methyl thioester) (TTMT) was synthesized via the reaction of thiophen-3-yl methanethiol with terephthaloyl dichloride. Nuclear magnetic resonance ( H-1-NMR) spectroscopy and Fourier transform infrared (FTIR) spectroscopy were utilized for the characterization of the monomer. Electrochemical copolymerization of TTMT with thiophene in acetonitrile/boron trifluoride diethyl etherate (AN/BFEE) (8:2, v/v) solvent mixture was realized by using tetrabutylammonium tetrafluoroborate (TBAFB) as the supporting electrolyte. The resulting copolymer was characterized via cyclic voltammetry (CV), FTIR, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), four-probe technique conductivity measurement and UV-Vis spectroscopy. Spectroelectrochemical analysis of the copolymer, P(TTMT-co-Th), reflected pi to pi* transition at 476 nm and band gap was calculated as 2.03 eV. Kinetic studies were carried out upon measuring the percent transmittance (%T=16%) at the maximum contrast point and switching time (1.25 s). A dual type electrochromic device (ECD) of P(TTMT-co-Th) and poly(3,4-ethylenedioxythiophene) (PEDOT) was constructed. Spectroelectrochemistry, switching ability, open circuit memory and stability of the device were examined by UV-Vis spectroscopy and cyclic voltammetry. The device switches between brown and blue, exhibits 0.0 V and 2.6 V as the switching voltages and short switching time (1.03 s).