Novel Fe(II)-Based Supramolecular Film Prepared by Interfacial Self-Assembly of an Asymmetric Polypyridine Ligand and Its Electrochromic Performance

An asymmetric two-arm polypyridine ligand 4'-{4-[4-(2,2'-dipyridyl)phenyl]}-2,2':6',2'-terpyridine (<b>TPY-Ph-BPY</b>) with double coordination units was synthesized using the one-step Suzuki reaction. The metallic supramolecular film was subsequently obtained by the Fe²⁺-induced self-assembly method at the CHCl₃-H₂O interface, which displayed a distinct flat and continuous morphology. The supramolecular film-coated ITO electrode demonstrated a reversible electrochemical redox behavior with pronounced color changes between purple and light green. Its solid-state electrochromic device had an optical contrast (Δ<i>T</i>%) of 26.2% at λ_max = 573 nm with balanced coloring (<i>t</i>_c = 2.4 s) and bleaching (<i>t</i>_b = 2.6 s) times and a high current efficiency of 507.8 cm²/C. Moreover, good cycling stability with a long-term reversible color change was observed beyond 900 cycles. These results suggested the promising potential of the <b>TPY-Ph-BPY-Fe(II)</b> supramolecular film for electrochromic applications.