Three novel donor-acceptor type electrochromic polymers containing 2,3-bis(5-methylfuran-2-yl)thieno[3,4-b]pyrazine acceptor and different thiophene donors: Low-band-gap, neutral green-colored, fast-switching materials

Abstract

Three novel donor-accept type electrochromic polymers with very low band gap, namely PMFTTP, PMFBTTP and PMFMOTTP, were prepared via electrochemical polymerization, employing 2,3-bis(5-methylfuran-2-yl)thieno[3,4-b]pyrazine as the acceptor units and thiophene, butylthiophen and methoxythiophen as the donor units, respectively. All the polymers were comparatively studied by cyclic voltammetry (CV), scanning electron micrographs (SEM), UV–vis-NIR spectroscopy and colorimetry. The results revealed that PMFTTP and PMFBTTP showed obvious color change from green color to brown in the oxidation process, while PMFMOTTP exhibited color change from brick red to dark gray. And the three polymers possessed very low optical band gaps in the following order: PMFTTP (1.23 eV) > PMFBTTP (0.88 eV) > PMFMOTTP (0.74 eV), which demonstrated the different election-donating ability of thiophene or its derivatives. The electrochromic kinetic investigations manifested that the polymers presented satisfactory optical contrasts (ΔT%) in the near infrared region (NIR), which were 35%, 67% and 60% for PMFTTP, PMFBTTP and PMFMOTTP, respectively. Moreover, the polymers also displayed short switching times (lower than 1 s at any wavelengths), high coloration efficiencies (around about 200 cm2/C) and outstanding robust stabilities, suggesting the probability of being the promising candidates for the electrochromic devices. In summary, the above positive results, especially the neutral green color and the very low band gap, had important theoretical significance for the application and development of electrochromic polymers.