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

Abstract

Nanocrystal surfaces play a critical role in dictating their physical and chemical properties. Colloidal semiconductor nanocrystals, or quantum dots, are generally synthesized with insulating aliphatic ligands, but these ligands can be post-synthetically exchanged with other molecular species for a variety of applications. While previous work has investigated the thermodynamics of ligand exchanges on quasi-spherical quantum dots through sensitive isothermal titration calorimetry and 1 H NMR measurements, the influence of well-defined crystal facets on the propensity of these ligand exchanges is yet to be explored using these techniques. We studied the exchange of native cadmium carboxylate ligands for zinc chloride ligands on (111) faceted cadmium selenide tetrahedrons and (100) faceted cadmium selenide cubes. From these measurements, we find the unexpected result that the thermodynamics of this ligand exchange between these facets is nearly identical. Further, a modified Ising model was used to fit both the calorimetric and 1 H NMR data to extract thermodynamic parameters for the exchange. These simulations suggest that the observed enthalpic differences can be mostly attributed to varying inter-ligand interactions on the ( 111) and (100) facets.

Ligand Exchange of Quantum Dots: A Thermodynamic Perspective

“…Besides, the exchanges of natural cadmium carboxylate (Cd(RCOOH) 2 ) with zinc chloride (ZnCl 2 ) on CdSe tetrahedra (111) and CdSe cubes (100) were investigated (Figure 9B). 90 From these measurements, unexpected results showed that the thermodynamics of ligand exchange between these surfaces were almost identical. In our group, ITC was used to obtain the thermodynamic parameters of EDA adsorbing onto the surface of QDs.…”

“…However, these indirect methods for studying thermodynamics have their limitations. With the well-known surface of QDs and the establishment of ligand exchange models, ITC, a direct method for monitoring thermal change, is increasingly used to study the thermodynamics of ligand exchange. ,− Thus, a more in-depth characterization of the ligand exchange can be conducted to reflect the most authentic ligand exchange. In addition to the coordination between the head groups of organic ligands and the surface of QDs, there is a weak noncovalent interaction between the tail groups of ligands.…”

“…Study of ligand exchange on different crystal faces of CdSe QDs through ITC (B). Reprinted with permission from ref . Copyright 2023 American Chemical Society.…”

“…In addition to revealing the conditions that lead to the instability of CsPbBr 3 NCs, the results of this study can also guide the intentional formation of 2D CsPb 2 Br 5 and 2D/3D CsPbBr 3 /CsPb 2 Br 5 composite structures for selected applications. Besides, the exchanges of natural cadmium carboxylate (Cd­(RCOOH) 2 ) with zinc chloride (ZnCl 2 ) on CdSe tetrahedra (111) and CdSe cubes (100) were investigated (Figure B) . From these measurements, unexpected results showed that the thermodynamics of ligand exchange between these surfaces were almost identical.…”