Colloidal nanocrystals offer flexible nanoscale platforms with unique optical and physical properties. Furthermore, such properties can be tuned by varying the nature and overall structure of the surface coating. Despite the remarkable advances in the growth and functionalization of these materials, information about the molecular arrangements of those ligands remains limited. We hereby apply several NMR spectroscopy techniques to characterize the ligand arrangements of both, as prepared hydrophobic colloidal nanocrystals and after phase transfer to water. We first combine the proton signatures of the ligands with diffusion ordered spectroscopy (DOSY) to distinguish surface-coordinated ligands from those freely-diffusing in the medium. We then combine 1H, 31P and HSQC spectroscopy techniques to identify the composition of the surface bound ligands. Finally, from comparison between the sharp signature(s) of specific groups in the surface-bound ligands to external standards we were able to extract estimates for the average number and stoichiometry of ligand compositions per nanocrystal.

Characterizing the organic coating of quantum dots using NMR spectroscopy

2019 Spring National Meeting

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