A Facile Method to Create a High-Performance Electrochromic Material: Electrografting of Bis-Terpyridine-Iron Motif onto Extended Indium Tin Oxide Support

Fe(II)–bis(terpyridine) units were covalently embedded on the extended surface of the indium tin oxide (ITO) support, and oligomeric molecular wires derived from these units were subsequently grown using a diazonium electrografting under ambient temperature and pressure. The resulting smart material exhibits excellent electrochromic performance, changing its optical properties in response to external voltage, both in a liquid electrolyte (3-electrode cell) and when assembled into a solid-state electrochromic device (2-electrode cell). Electrografting molecular architectures within interparticle pores results in dense molecular packing, as confirmed by surface coverage measurements and the presence of π–π* satellites in both the C 1s and N 1s X-ray photoelectron spectra. Electrografting is more time-efficient than the conventional layer-by-layer growth of coordination-based molecular assemblies. Moreover, it eliminates the need for a separate surface templating layer, resulting in enhanced conductivity through the molecular wire. Thus, the electron transfer rate of the developed material is in par with that of monolayer-based materials. The electrochromic devices were assembled by incorporating the material and surface-enhanced ITO as electrodes through a lithium gel electrolyte and a Nafion layer. In-operando measured optical properties demonstrate that the device exhibits extremely high cycling stability, notable coloration efficiency, and short switching times.