| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Nanomaterials | Monday Sessions |
| Session NM-MoM |
| Session: | Nanocharacterization |
| Presenter: | Sara Smock, University of Southern California |
| Authors: | S.R. Smock, University of Southern California R.L. Brutchey, University of Southern California |
| Correspondent: | Click to Email |
The characterization of surface ligand binding to quantum dots is important to fully understand their behavior, such as photoluminescence quantum yield. One of the most promising recent classes of quantum dot materials is the CsPbX3 halide perovskites (where X = Cl–, Br–, I–) because of their growing applications in LEDs, X-ray detectors, and lasers. These CsPbX3 quantum dots possess bright photoluminescence and narrow emission line widths over a wide color gamut. Using the hot-injection synthesis first reported by Protesescu et al. (Nano Lett.2015, 15, 3692), the ligand shell supporting the resulting CsPbBr3 quantum dots has been reported to be highly dynamic and primarily comprised of oleylammonium bromide binding to the surface in an NC(X)2 fashion without accompanying oleate X-type coordination. To date, however, the characterization of ligand binding has been qualitative in nature. Herein, we will report on quantifying the thermodynamics of n-alkyl carboxylic acid and amine ligand binding to CsPbBr3 quantum dots via 1H NMR spectroscopy. 1H NMR is a powerful characterization tool for organic ligands on the surfaces of nanocrystals to observe ligand binding and gain insight into the thermodynamics of ligand exchange processes. In agreement with previous studies, we find the supporting ligands to be fluxional in nature; however, both ammonium and carboxylate binding to the purified nanocrystal surface is unequivocally observed. n-Alkyl carboxylic acids undergo an exergonic exchange equilibrium with bound oleate (Keq = 1.97) at 25 ˚C, while n-alkyl phosphonic acids undergo an irreversible ligand exchange. n-Alkyl amines exergonically exchange with oleylamine (Keq = 2.52) at 25 ˚C. Exchange occurs with carboxylic acids, phosphonic acids, and amines on CsPbBr3 quantum dots without etching the nanocrystal surface; increases in steady-state PL intensities are correlated with more strongly bound conjugate base ligands.