Quantifying the thermodynamics of ligand binding to CsPbBr₃ 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, ¹H NMR methods were used to quantify the thermodynamics of ligand exchange on CsPbBr₃ QDs. Both oleic acid and oleylamine native ligands dynamically interact with the CsPbBr₃ QD surface, having individual surface densities of 1.2-1.7 nm^-2. 10-Undecenoic acid undergoes an exergonic exchange equilibrium with bound oleate (K_eq=1.97) at 25 C while 10-undecenylphosphonic acid undergoes irreversible ligand exchange. Undec-10-en-1-amine exergonically exchanges with oleylamine (K_eq=2.52) at 25 C. Exchange occurs with carboxylic acids, phosphonic acids, and amines on CsPbBr₃ QDs without etching of the nanocrystal surface; increases in the steady-state PL intensities correlate with more strongly bound conjugate base ligands. (copyright 2018 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)