Calibrating ligand-ligand interaction on nanocrystals via the dynamic volume of chain segments

Ligand-ligand interaction is crucial for the surface chemistry, solution properties, and self-assembly processes of colloidal nanocrystals (NCs). Studies on the ligand-ligand interaction are hampered by the disordered and dynamic nature of the surface, the low electron contrast of organic moieties, and the non-characteristic weak intermolecular forces. Solid-state nuclear magnetic resonance (SSNMR) can provide site-specific information on organic ligands and especially the motional behavior of chain segments. Here, we report an advanced SSNMR measurement and modeling strategy to quantify the “dynamic volume” of chain segments. The dynamic volume depicts the accessible space of a chain segment under the confinement of neighboring molecules and is inversely proportional to the intermolecular interaction energy. We show that the calculated ligand-ligand interaction energy determines the solution dispersity and melting transitions of NCs. This dynamic volume concept can be extended beyond experimental measurements and offer semi-empirical predictions of the interaction energies of alkanoate ligands.