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Synthesis, characterization and electrochromic properties of conducting copolymers of terephthalic acid bis-(thiophen-3-ylmethyl)thioester with thiophene and pyrrole and conducting polymer of 1-(4-fluorophenyl)-2,5-di(thiophen-2-yl)-1h-pyrrole

Türkarslan, Özlem
Terephthalic acid bis-(thiophen-3-ylmethyl)thioester (TTMT) was synthesized via the reaction of thiophen-3-ylmethanethiol with terephthaloyl dichloride. Nuclear magnetic resonance (1H-NMR) and Fourier transform infrared (FTIR) spectroscopies were utilized for the characterization of the monomer. This 3-functionalized thiophene monomer was polymerized in the presence of thiophene (Th) and pyrrole (Py) upon constant potential application in acetonitrile/tetrabutylammonium tetrafluoroborate (TBAFB). The resulting copolymers were 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 P(TTMT-co-Th) revealed π to π* transition at 476 nm with a band gap of 2.0 eV whereas, λmax and Eg were found as 375 nm and 2.4 eV for P(TTMT-co-Py), respectively. Dual type electrochromic devices (ECDs) of P(TTMT-co-Th) and P(TTMT-co-Py) with poly(3,4-ethylenedioxythiophene) (PEDOT) were constructed. Spectroelectrochemistry, switching ability, open circuit memory and stability of the devices were examined by UV-Vis spectroscopy and cyclic voltammetry. The device P(TTMT-co-Th)/PEDOT switches between brown and blue upon application of 0.0 V and +2.6 V, respectively with 11% optical contrast and 1.1 s as the switching time. On the other hand, P(TTMT-co-Py)/PEDOT ECD exhibits greenish yellow, grayish red and blue colors with the application of -2.4 V, 0.0 V and +0.8 V, respectively and the contrast between extreme potentials was 17.5% with a switching time of 1.6 s. 1-(4-Fluorophenyl)-2,5-di(thiophen-2-yl)-1H-pyrrole (FPTP) was synthesized and polymerized both chemically and electrochemically. Several analytical techniques, such as NMR, FTIR, CV, gel permeation chromatography (GPC), four-probe conductivity measurement, SEM were utilized when applicable. Spectroelectrochemistry experiments reflected a π to π* transition at 398 nm with a band gap energy of 1.94 eV for the polymer. A dual type electrochromic device (ECD) of PFPTP and poly(3,4-ethylenedioxythiophene) (PEDOT) was constructed. The device switches between yellowish brown and blue upon application of 0.8 V and +1.1 V, respectively. Optical contrast was calculated as 19.4% with a switching time of 1.4 s at maximum contrast point.