Impact of solvent and ligand density on the self-assembly and optical properties of metal nanocrystals

Metal nanocrystals (M-NCs) and their supramolecular assemblies have attracted significant interest from the scientific community due to their wide range of applications arising from the possibility of accurately tuning the M-NCs properties through self-assembly into supramolecular aggregates. In this study, we investigate the complex interplay between capping agent surface coverage and solvent-capping agent interactions in the self-assembly process of M-NCs into supramolecular structures. Specifically, we explore the self-assembly behavior of gold (Au-NCs), silver (Ag-NCs), and platinum (Pt-NCs) nanocrystals upon functionalization with oleic acid (OA) in water using a microemulsion approach. Through a multi-technique analysis, we demonstrate the critical role of ligand density and solvent choice in driving the formation of highly ordered supramolecular structures. By increasing the surface coverage of the M-NC ligands, we observed a transition to more organised assemblies, with the interaction between the oleylamine alkyl chain and the functionalization medium further modulating the type of supramolecular arrangement. Moreover, we highlight the profound influence of both the external environment and supramolecular aggregation on the optical properties of the M-NCs. This work provides crucial insights into the factors that govern nanocrystals' self-assembly and optical behavior, with broad implications for the design and application of nanomaterials in nanotechnology and materials science.