Tethering functional molecular structures to the surface of semiconductor nanocrystals is an important strategy for implementing applications of these materials. However, engineering of the newly developed perovskite nanocrystals (PNCs) was rarely reported due to the difficulty of stably grafting functional groups on PNCs’ highly dynamic surfaces. In light of this, we systematically evaluated the bound affinity of a series of common chemical motifs, including ligands with heterocyclic bidentate coordination groups and aromatic zwitterions that provide both covalent and ionic binding sites on the surface of colloidal CsPbBr<sub>3</sub> PNCs. Using NMR, FT-IR spectroscopy, and DFT calculations, we obtained a fine-scale of the relative surface bound affinity for these ligands and used this scale to guide the design of a two-step functionalization strategy for PNCs. First, ligands with appropriate bound affinity were applied in a precipitation-redissolution purification procedure for protecting the PNC from degradation and agglomeration. The purification step does not only prevent the interference of residual synthetic ligands in the functionalization step but also prepares the PNC surface for ligand exchange. In the second step, the reconstructed PNC surface was modified by replacing the ligands introduced in the purification step with functional chemical structures possessing stronger binding motifs. In this work, we demonstrated the anchoring of molecular charge carrier acceptors. Steady-state and time-resolved optical spectroscopic methods are employed to monitor photoinduced charge transfer and triplet energy transfer across the interface between the inorganic perovskite core and different organic acceptors grafted using this surface engineering strategy. The successful coupling of functional groups on the PNC surface opens opportunities for designing efficient sensitizers for photocatalysis and fabricating PNC-based nanoprobes.

Reconstructing the surface of colloidal lead halide perovskite nanocrystals for functionalization

ACS Spring 2022

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