Quantifying the Thermodynamics of Ligand Binding to CsPbBr Quantum Dots.

Cesium lead halide perovskites are an emerging class of quantum dots (QDs) that have shown promise in a variety of applications; however, their properties are highly dependent on their surface chemistry. To this point, the thermodynamics of ligand binding remain unstudied. Herein, H NMR methods were used to quantify the thermodynamics of ligand exchange on CsPbBr QDs. Both oleic acid and oleylamine native ligands dynamically interact with the CsPbBr QD surface, having individual surface densities of 1.2-1.7 nm . 10-Undecenoic acid undergoes an exergonic exchange equilibrium with bound oleate (K =1.97) at 25 °C while 10-undecenylphosphonic acid undergoes irreversible ligand exchange. Undec-10-en-1-amine exergonically exchanges with oleylamine (K =2.52) at 25 °C. Exchange occurs with carboxylic acids, phosphonic acids, and amines on CsPbBr QDs without etching of the nanocrystal surface; increases in the steady-state PL intensities correlate with more strongly bound conjugate base ligands.