At the outermost surface of colloidal QDs are organic surface ligands which dynamically bind and release in solution to control the growth kinetics, control the size/shape of the crystals, passivate surface states, and provide colloidal stability through favorable interactions with the solvent. However, the dynamicity comes at the expense of the stability of the QD suspension. Here, we show that ligands can be permanently locked on the QD surface by a thin layer of an inert metal oxide which forms within the ligand shell, over the headgroup. By interrogating the surface chemistry with different spectroscopic methods, we prove the ligand locking on the QD surface. As a result, an exceptional stability of the coated QD inks is achieved in a wide concentration range, even in the presence of chemically competing surface ligands in solution. We anticipate that this critical breakthrough will benefit different areas related to colloidal QDs, spanning from single-particle studies to displays and solar cells and biological applications. Furthermore, the same chemistry could be easily translated to surface treatments of bulk materials and thin films.

Colloidal atomic layer deposition (c-ALD) enables the growth of hybrid organic–inorganic oxide shells with tunable thickness at the nanometer scale around ligand-functionalized inorganic nanoparticles (NPs). This recently developed method has demonstrated improved stability of NPs and of their dispersions, a key requirement for their application. Nevertheless, the mechanism by which the inorganic shells form is still unknown, as is the nature of multiple complex interfaces between the NPs, the organic ligands functionalizing the surface, and the shell. Here, we demonstrate that carboxylate ligands are the key element that enables the synthesis of these core–shell structures. Dynamic nuclear polarization surface-enhanced nuclear magnetic resonance spectroscopy (DNP SENS) in combination with density functional theory (DFT) structure calculations shows that the addition of the aluminum organometallic precursor forms a ligand–precursor complex that interacts with the NP surface. This ligand–precursor complex is the first step for the nucleation of the shell and enables its further growth.

Colloidal nanocrystals (NCs) are ideal materials for a variety of applications and devices, which span from catalysis and optoelectronics to biological imaging. Organic chromophores are often combined with NCs as photoactive ligands to expand the functionality of NCs or to achieve optimal device performance. The most common methodology to introduce these chromophores involves ligand exchange procedures. Despite their ubiquitous nature, ligand exchanges suffer from a few limitations, which include reversible binding, restricted access to binding sites, and the need for purification of the samples, which can result in loss of colloidal stability. Herein, we propose a methodology to bypass these inherent issues of ligand exchange through the growth of an amorphous alumina shell by colloidal atomic layer deposition (c-ALD). We demonstrate that c-ALD creates colloidally stable composite materials, which comprise NCs and organic chromophores as photoactive ligands, by trapping the chromophores around the NC core. As representative examples, we functionalize semiconductor NCs, which include PbS, CsPbBr 3 , CuInS 2 , Cu 2−x X, and lanthanide-based upconverting NCs, with polyaromatic hydrocarbons (PAH) ligands. Finally, we prove that triplet energy transfer occurs through the shell and we realize the assembly of a triplet exciton funnel structure, which cannot be obtained via conventional ligand exchange procedures. The formation of these organic/inorganic hybrid shells promises to synergistically boost catalytic and multiexcitonic processes while endowing enhanced stability to the NC core.

The combination of porous reticular frameworks and nanocrystals (NCs) offers a rich playground to design materials with functionalities, which are beneficial for a large variety of applications. Achieving compositional and structural tunability of these hybrid platforms is not trivial, and new approaches driven by the understanding of their formation mechanism are needed. Here, we present a synthetic route to encapsulate NCs of various sizes, shapes, and compositions in the microporous imine-linked covalent organic framework (COF) LZU1. The tunable NC@LZU1 core–shell hybrids are synthesized by combining colloidal chemistry and homogeneous microwave-assisted syntheses, an approach that allows tailoring of the shell thickness while ensuring COF crystallinity in the presence of the NCs. The uniform morphologies of these new composite materials along with their colloidal nature enable insights into their formation mechanism. Having learned that the COFs heterogeneously nucleate on the NC seeds, we further expand the synthetic approach by developing a step-by-step encapsulation strategy. Here, we gain control over the spatial distribution of various NCs within multilayered NC@LZU1@NC@LZU1 core–shell–core–shell hybrids and also form yolk–shell nanostructures. The synthetic route is general and applicable to a broad variety of NCs (with catalytic, magnetic, or optical properties), thus revealing a new way to impart functionalities to COFs.

Atomically controlled multicomponent nanomaterials have advanced the understanding of scientific phenomena and devised solutions to practical problems, enabling technological progress in many application fields.