Ligand exchange chemistry of metal chalcogenide nanocrystals is essential for functionalizing these materials for a variety of applications, ranging from photovoltaics to biological imaging. Many studies report qualitative changes in photoluminescence as evidence for the exchange of native, L-type ligands (such as tri-n-octylphosphine oxide) for functional Lewis bases (pyridine, primary amines, thiols). However very seldom is ligand exchange monitored directly or in situ, and often these results are convoluted by side reactions that occur between excess metal ions or organic X-type ligands at the nanocrystal surface. We report a series of L-type ligand exchanges using tri-n-butylphosphine-bound, chloride-terminated CdSe nanocrystals with several ligand classes, including aromatic, cyclic, and non-cyclic sulfides, ethers, and amines; primary, secondary, and tertiary amines and phosphines; tertiary phosphine chalcogenides; primary thiols, alcohols, isocyanides, and isothiocyanides; and N-heterocylic carbenes.  Using 31P NMR spectroscopy, we establish a relative binding affinity for these ligands which reflects electronic considerations but is dominated primarily by steric interactions. This information should provide insight for rational ligand design for future applications involving metal chalcogenide nanocrystals.

Relative binding affinity of L-type ligands for chloride-terminated CdSe nanocrystals

247th National Meeting (2014)

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