Iron Phthalocyanine Incorporated Metallo-Supramolecular Polymer for Superior Electrochromic Performance with High Coloration Efficiency and Switching Stability

In this study, we newly synthesized iron phthalocyanine incorporated iron metallo-supramolecular polymers (Pc-Fe-polymer) and investigated its electrochromic behavior in both solution and solid-state devices. The presence of a terpyridine-attached iron phthalocyanine (FePc-TP) spacer revealed long-wavelength absorption at 670-700 nm, and the metal-to-ligand charge transfer (MLCT) by Fe-terpyridine coordination induced another absorption at 578 nm. Consequently, the Pc-Fe-polymer covered broad ranges of visible and near-infrared regions. Furthermore, due to facile charge delocalization during the Fe²⁺ to Fe³⁺ redox process, the Pc-Fe-polymer exhibited enhanced electrochromic performances. The Pc-Fe-polymer film experienced reversible electrochromic switching by changing the color from dark blue to transparent green in both solution and solid-state devices using LiClO₄ as an electrolyte. The Pc-Fe-polymer exhibited exceptionally high switching stability (>1000 times) and a high coloration efficiency of 346.7 cm²/C and 211.4 cm²/C in solution and solid-state devices, respectively. Besides, we successfully demonstrated the feasibility of applying the Pc-Fe-polymer for flexible electrochromic devices on a plastic substrate. This study's results suggest a designing concept for electrochromic materials that have highly stable and efficient switching for smart display and window applications.