Interfacial self-assembly of a rigid-flexible terpyridine-Fe(ii) supramolecular film and the electrochromic performance of its solid-state devices

Abstract

A novel three-arm terpyridine ligand L with flexible methylenoxyl (–CH₂–O–) groups was synthesized by a one-step chemical reaction, and the uniform two-dimensional supramolecular films with various sizes and thicknesses were simply prepared on the surface of indium tin oxide (ITO) conductive glass by an Fe²⁺-induced self-assembly method at the dichloromethane–water interface. The morphology, structure and composition were confirmed by ultraviolet-visible (UV-vis) absorption spectroscopy, scanning electron microscope/energy dispersive spectrometer (SEM/EDS), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS), respectively. The sandwiched solid-state devices (1.3 × 1.4 cm²), fabricated by employing L-Fe film coated ITO as the electrochromic layer and LiClO₄/poly(methyl methacrylate) (PMMA)/propylene carbonate (PC)/CH₃CN based gel as the supporting electrolyte, showed a reversible color change from purple to light yellow with the optical contrast (ΔT%) of 56.6%, the coloring and bleaching times of 3.9 s and 3.7 s, and the coloring and bleaching efficiencies of 875.2 cm² C⁻¹ and 182.3 cm² C⁻¹ under the applied double-step voltages of −2.0 V and +3.0 V. The device had good stability, maintaining 70% of its initial optical contrast after 500 cycles. Meanwhile, a large-sized solid-state device with an active area of 7 × 7 cm² showed its application potential in smart windows or displays.