Tunable electrochromic behavior of biphenyl poly(viologen)-based ion gels in all-in-one devices

Electrochromic (EC) materials have attracted considerable attention for various applications, such as smart windows, information displays, and functional energy storage devices. In particular, poly(viologen) are promising EC materials owing to their flexible color tunability depending on the N-substituents and molecular weight. In this study, a new poly(viologen) containing biphenyl group and viologen (denoted as BP-poly(viologen)) was synthesized and employed in ion gel-based-EC devices (ECDs). Hydroquinone (H2Q) was used as the anodic species, and the H2Q/BP-poly(viologen) mole ratio was adjusted to obtain a balanced charge for the desired redox states of BP-poly(viologen). The resulting ECDs exhibited three different colors depending on the redox states of BP-poly(viologen): orange (dications), green (radical cations), and purple (neutral species). Color-switchable EC displays with various patterns were demonstrated using electro-force-assisted dispensing printing.