Colloidal Phase Control in Plasmonic Metal Oxide Nanocrystals via Competitive Metal-Ligand Equilibria

Colloidal nanocrystal gels offer tunable optical properties governed by both the nature of the building blocks and their spatial arrangement. When assembled via reversible molecular linkers, their phase behavior and structure are primarily dictated by bond strength and lability. However, precise control over these interactions remains a significant synthetic challenge and is often system-specific. Here, we present a simple, broadly tunable linking strategy that modulates nanocrystal phase behavior and assembly structure by leveraging competitive metal-ligand equilibria. We achieve programmable control over gelation temperature and network structure by tuning competitive metal-terpyridine and metal-halide equilibria in terpyridine-functionalized tin-doped indium oxide (ITO) nanocrystals, governed by metal and halide identity, concentration, and temperature, enabling wide-range infrared optical modulation. Combined kinetic Monte Carlo and optical simulations reveal that weaker, more labile links facilitate particle crawling, leading to denser gel structures with enhanced plasmon coupling. This strategy eliminates the need for complex ligand or linker design and establishes competitive coordination chemistry as a versatile platform for engineering dynamic, stimuli-responsive colloidal assemblies.