Colloidal nanocrystals made of transition metal cores, prepared via bottom-up solution growth routes, offer great promises for use in wide range of applications and as functional platforms for integration in biomedicine. To facilitate these uses, we have developed a set of high affinity metal-coordinating polymers that are optimally-adapted for surface functionalizing a variety of inorganic nanocrystals. The ligand design exploits the effectiveness of the one-step nucleophilic addition reaction to simultaneously introduce several “custom-adapted” anchoring groups along with solubilizing blocks and reactive functionalities into a single macromolecule. We have more recently used this strategy to test the ability of N-heterocyclic carbene (NHC)-modified ligands to coordinate and stabilize luminescent CdSe-ZnS core-shell quantum dot (QD) dispersions in hydrophilic media. In particular, we probed the effects of ligand structure and coordination on the coating affinity to the nanocrystals.  We find that such NHC-based ligands rapidly coordinate onto the QDs (requiring ~ 10 min of reaction time), which reflects the soft Lewis base nature of the NHC groups, with its two electrons sharing capacity. Removal of the hydrophobic cap and promotion of carbene-driven coordination on the nanocrystals have been verified by <sup>1</sup>H NMR spectroscopy, while <sup>13</sup>C NMR was used to identify the formation of carbene-Zn complexes. The newly-coated QD dispersions exhibit great long term colloidal stability over a wide range of conditions. Additionally, we find that coordination onto the QD surfaces affects the optical and spectroscopic properties of the nanocrystals. These include a size-dependent red-shift of the absorption and fluorescence spectra and a pronounced increase in the measured fluorescence intensity when the samples are stored under white light exposure, compared to those stored in the dark.

Stabilizing and functionalizing inorganic nanocrystals via metal-ligand coordination interactions

ACS Fall 2021

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