Superlattice Assembly for Empowering Metal Nanoclusters

ConspectusAtomically precise metal nanoclusters, serving as an aggregation state of metal atoms, display unique physicochemical properties owing to their ultrasmall sizes with discrete electronic energy levels and strong quantum size effects. Such intriguing properties endow nanoclusters with potential utilization as efficient nanomaterials in catalysis, electron transfer, drug delivery, photothermal conversion, optical control, etc. With the assistance of atomically precise operations and theoretical calculations on metal nanoclusters, significant progress has been accomplished in illustrating their structure-performance correlations at the single-molecule level. Such research achievements, in turn, have contributed to the rational design and customization of functional nanoclusters and cluster-based nanomaterials.Most previous studies have focused on investigating structure-property correlations of nanocluster monomers, while the exploration of electronic structures and physicochemical properties of hierarchical cluster-based assembled structures was far from enough. Indeed, from the application aspect, the nanoclusters with controllably assembly states (e.g., crystalline assembled materials, host-guest hybrid materials, amorphous powders, and so on) were more suitable for performance expression relative to those in the monomeric state and more directed to downstream solid-state applications. In this context, more attention should be paid to the state-correlated property variations of metal nanoclusters occurring in their aggregating and assembling processes for better applications in accordance with their aptitude.Crystalline aggregates are crucial in the structural determination of metal nanoclusters, also acting as a cornerstone to analyze the structure-property correlations by affording atomic-level information. The regular arrangement, uniform composition, and close intermolecular distance of the cluster molecules in their supercrystal lattices are beneficial for property retention and amplification from the molecule itself as a monomeric state. Besides, for these nanoparticles with strong quantum size effects, the intercluster distances in the supercrystal lattices are still located at the nanoscale level, wherein the quantum size effect is highly likely to take effect with additional intermolecular synergistic effects. Accordingly, it is expected that novel performances might occur in the crystalline aggregates of nanoclusters that are completely different from those in the monomolecular state.In this Account, we emphasize our efforts in exploring the performance enhancement of atomically precise metal nanoclusters in their crystalline aggregate states, such as thermal stability, photoluminescence, optical activity, and an optical waveguide. Such performance enhancements further supported the practical uses of metal nanoclusters in structure determination, a polarization switch, an optical waveguide device, and so on. We also demonstrated that the differences in physicochemical properties between crystalline aggregates and monomers of metal nanoclusters might be attributed to the change in electronic structures during the crystalline aggregation processes in the superlattice. The "superlattice assembly" is intended to customize the function of cluster-based aggregates for downstream solid-state applications.