Adjustable optoelectronic properties of triphenylamine-ethylenedioxythiophene based hybrid electrochromic polymer with different electron-donating substituents

Abstract

Due to the good optoelectronic properties of triphenylamine (TPA) and its derivatives-based organic conjugated polymers, they have been widely used in various organic electronic devices. They are easy to lose electrons to form stable cationic free radicals with color change under electrochemical oxidation conditions. Therefore, TPA derivatives-based electrochromism materials have attracted the widely attentions of researchers. In this work, a series of TPA derivatives were successfully obtained by Stille coupling reactions, and their basic optical and electrical properties were investigated in detail. Their corresponding polymer films (P(TPA-EDOT), P(PhTPA-EDOT), and P(OCH3TPA-EDOT)) were also prepared on transparent ITO glass by electrodeposition method and their electrochromic properties were further studied. Due to the relatively strong electron donating ability of OCH3– group on the TPA unit, the intramolecular charge transfer peak of OCH3TPA-EDOT is obvious red-shifted and its initial oxidation potential is relatively low, which is beneficial for it to get high-quality electrochromic polymers. Electrochemical analysis shows that all these three polymer films show reversible redox reaction with excellent redox stability. Spectroelectrochemistry shows that all of them have good electrochromic properties and show multi-electrochromic behavior with strong color change. The dynamic study show that all these three polymers have relatively fast switching time (as low as 0.8 s), high coloration efficiency (up to 206.2 C−1 cm2) and obvious optical contrast change. Especially in the near infrared region, the optical contrast is relatively high (P(TPA-EDOT) is 45.3 % at 1100 nm, P(PPhTPA-EDOT) is 53.1 % at 1100 nm, and P(OCH3TPA-EDOT) is 57.2 % at 1100 nm). All these results show that the different substituents on the TPA unit have a certain influence on the resultant monomers’ optoelectronic performances, and they also can adjust the optical band gap of the corresponding polymers with different electrochromic properties.