Electrically and Thermally Controllable Visible‐to‐Near‐Infrared Light Trapping Smart Window with Tunable Optical States

Abstract In this work, active viologen anchored on poly(2‐isopropyl‐2‐oxazoline) (PiPO) segments spaced with triazole‐bearing oxyethylene chain (POE_m‐PiPO‐HPV) molecule is discovered to be an effective single‐component dual‐band chromic material. Unlike most reported materials of this type, POE_m‐PiPO‐HPV not only is electrochromic but thermochromic as well, showing optical switching from clear to hazy at ≈55–59 °C as a result of phase transformation when triggered by heat attaining >60% optical contrast (ΔT) both in the visible and near infrared (NIR) range. Likewise, >75% ΔT is achieved when switched from clear state to colored state at an applied potential (≈0.45–2.9 V). Each distinct mode of chromism uniquely and autonomously modulates visible and NIR light. Multiple color states—hazy, burgundy, brown, dark purple, and royal blue—are also displayed when the spacer length is modified and when the counteranions undergo metathesis. A coloration speed of 25 s resulting in purple color and a bleaching speed of 11 s are attained by PiPO with hepta‐oxyethylene chain and hexafluorophosphate anion (POE₇‐PiPO‐HPV‐PF₆) with a coloration efficiency of 295.0 cm² C⁻¹ and cyclic stability of >200 cycles.