Transmissive-to-Black Electrochromic Switching of Pendant Viologen Polymer with Superior Long-Term Operation Stability

Electrochromic devices (ECDs) have evolved significantly with advancements in electrochromic materials. Viologen-based ECDs, known for their tunable electrochromic properties, face challenges such as low cyclic lifetime and electrolyte leakage. This study introduces poly-APPV, a pendant viologen polymer exhibiting transmissive-to-black electrochromic switching. The polymer offers enhanced long-term stability and rapid switching times, effectively addressing these challenges. The synthesis of allyl viologen, [APPV][PF₆]₂, and poly-APPV is successfully characterized using ¹H-NMR, FT-IR, and GPC analyses. Cyclic voltammetry reveals diffusion-controlled redox reactions, while electrochemical impedance spectroscopy shows acceptable ionic conductivity of poly-APPV. Spectroelectrochemical studies indicate significant transmittance changes, with poly-APPV exhibiting a lower operating voltage and superior transmittance difference. Long-term stability tests confirm superior optical density and high coloration efficiency of poly-APPV. Overall, the pendant viologen polymer’s enhanced properties make it a promising material for electrochromic applications. These findings prove the benefits of polymerized viologens in enhancing electrochromic performances, offering valuable insights for developing next-generation electrochromic systems.