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Colloidal lead halide perovskite quantum dots (PQDs) are relatively new semiconductor nanocrystals with great potential for use in optoelectronic applications. They also present a set of new scientifically challenging fundamental problems to investigate and understand. One of them is to address the rather poor colloidal and structural stability of these materials under solution phase processing and/or transfer between solvents. In this contribution, we detail the synthesis of a new family of multi-coordinating, bromide-based polysalt ligands and test their ability to stabilize CsPbBr 3 nanocrystals in polar solutions. The ligands present multiple salt groups involving quaternary cations, namely ammonium and imidazolium as anchors for coordination onto PQD surfaces, along with several alkyl chains with varying chain length to promote solubilization in various conditions. The ligands provide a few key benefits including the ability to repair damaged surface sites, allow rapid ligand exchange and phase transfer, and preserve the crystalline structure and morphology of the nanocrystals. The polysalt-coated PQDs exhibit near unity PLQY and significantly enhanced colloidal stability in ethanol and methanol. 

We designed a novel multicoordinating ligand based on the N-heterocyclic carbene (NHC) anchoring molecules and applied them for stabilizing luminescent quantum dots in aqueous media. The ligand is synthesized via nucleophilic addition reaction between amine-appended imidazole/poly(ethylene glycol) compounds and poly(isobutylene-alt-maleic anhydride) (PIMA), followed by carbene generation. We find that these NHC-based polymers exhibit fast and robust coordinating affinity to CdSe QDs overcoated with ZnS shells. The removal of hydrophobic coating and the generation of carbene are demonstrated by 1H NMR spectroscopy. 13C NMR spectroscopy confirms the existence of carbene-Zn complexes which is crucial for binding transition-metals on QD surfaces. These QDs exhibit absorption and emission features with little to no change before and after cap exchange, and their PL intensity is increased under light exposure. Excellent colloidal stability of these QD samples is observed in a wide range of competitive conditions over long period of time. Agarose gel electrophoresis indicates that the polymer coating imparts QDs with good compatibility in different aqueous buffers, and it prevents protein adsorption.