Tuning the Morphology of Self-Assembled Au Nanocluster Sheets by Controlling Solvent-Ligand Interactions

The precise assembly of colloidal nanoparticles into ordered 2D structures remains challenging due to complex interparticle interactions and variable particle size, shape, and surface chemistry. Herein, we present a facile strategy for the 2D self-assembly of atomically precise Au nanoclusters protected by dodecanethiolate ligands into freestanding monolayer sheets under ambient conditions. The solvent polarity is modified to control interligand and solvent-ligand interactions, successfully tuning the morphology of the nanocluster superstructures without templates or annealing. In non-polar solvents, the extended alkyl ligands promote directional dipole-dipole alignment into 1D chains, which laterally interdigitate into well-ordered 2D nanosheets. In low-polarity solvents, the reduced solvophilicity enhances lateral cohesion, forming larger sheets with smooth edges. In contrast, high-polarity solvents induce collapsed ligand conformations and random aggregation; however, heating supplies sufficient thermal energy to improve ligand flexibility and solvation, enabling reassembly into ordered 2D structures upon cooling. Furthermore, the post-synthesis addition of acetone and oleylamine as secondary ligands induced edge folding and sheet rolling, respectively. This approach underscores the potential of rationally tuning nanoscale interactions to achieve colloidal assemblies with precise structures.