Synthesis And Electrochromic Properties Of Conjugated Polymers Containing Thieno[3,4-b]pyrazine Units

The organic ?-conjugated polymers(CPs) have been developed into the extremely promising conducting materials and were widely applied in the fields of organic field-effect transistors, organic light emitting diodes, electrochromic devices, photovoltaics, etc. Due to optical band gaps of the CPs play an important role to accomplish desired applications, there are many methods for regulating the optical band gap of the ?-conjugated polymer. Alternating electron-rich(the donor moiety, D) and electron-poor(the acceptor moiety, A) units can increase the HOMO level or decrease the LUMO level, which tuned the optical band gaps of the D-A type conjugated polymers. So the donor-acceptor method provides an adoptable pathway to obtain the desired electrochromic polymers with low band gaps and specific colors.Electrochromic polymers(ECPs) are known as a reversible and visible color change which is connected with an electrochemically caused oxidation or reduction. Since the electrochromic polymers can show outstanding coloration efficiencies, fast response times, fine-tunability of bandgaps, high optical contrasts and excellent processability, they have been envisioned as one of the most favored electrochromic materials in optical displays, devices, camouflage materials, smart windows, and rear-mirrors for cars.In this study, monomers were successfully designed based on donor-acceptor theory(D-A theory) and synthesized via dehydration condensation reaction. Nine donor-accept type organic ?-conjugated conducting polymers(PMFTTP, PMFBTTP, PMFMOTTP, PBTBTQ, PBTTPP, PMPTTP, PDPTTP, PMPBTTP and PDPBTTP) were synthesized by electropolymerization method, using thieno[3,4-b]pyrazine derivatives as the acceptor units and thiophene or its derivatives as the donor units. Electrochemical, morphological and spectroelectrochemical properties of these polymers were characterized using cyclic voltammetry(CV), scanning electron micrographs(SEM) and UV-vis-NIR spectroscopy.Electrochemical and spectroelectrochemical studies demonstrate that all of the polymers showed lower onset oxidation potentials(lower than 0.43 V), lower optical band gaps(lower than 1.26 eV) and robust electrochemical stabilities. It is worth mentioning that the PMFTTP, PMFBTTP, PMPTTP, PDPTTP, PMPBTTP and PDPBTTP polymer films showed green neutral states and highly transmissive oxidized states. Furthermore, electrochromic kinetic investigations showed that all nine polymers displayed excellent optical contrasts(greater than 32%), fast switching times(lower than 1.80 s), high coloration efficiencies(greater than 60.77 cm2 C-1) and excellent dynamics stabilities. Regarding these superior electrochemical and optical properties, the nine polymers would probably be a promising choice for developing electrochromic devices.