Impact of Uniform Facets on the Thermodynamics of Ligand Exchanges on Colloidal Quantum Dots

Nanocrystal surfaces play a critical role in dictatingtheir physicaland chemical properties. Colloidal semiconductor nanocrystals, orquantum dots, are generally synthesized with insulating aliphaticligands, but these ligands can be post-synthetically exchanged withother molecular species for a variety of applications. While previouswork has investigated the thermodynamics of ligand exchanges on quasi-sphericalquantum dots through sensitive isothermal titration calorimetry and H-1 NMR measurements, the influence of well-defined crystalfacets on the propensity of these ligand exchanges is yet to be exploredusing these techniques. We studied the exchange of native cadmiumcarboxylate ligands for zinc chloride ligands on (111) faceted cadmiumselenide tetrahedrons and (100) faceted cadmium selenide cubes. Fromthese measurements, we find the unexpected result that the thermodynamicsof this ligand exchange between these facets is nearly identical.Further, a modified Ising model was used to fit both the calorimetricand H-1 NMR data to extract thermodynamic parameters forthe exchange. These simulations suggest that the observed enthalpicdifferences can be mostly attributed to varying inter-ligand interactionson the (111) and (100) facets.