Ligand protected noble metal nanoparticles are excellent building blocks for colloidal self‐assembly. Metal nanoparticle self‐assembly offers routes for a wide range of multifunctional nanomaterials with enhanced optoelectronic properties. The emergence of atomically precise monolayer thiol‐protected noble metal nanoclusters has overcome numerous challenges such as uncontrolled aggregation, polydispersity, and directionalities faced in plasmonic nanoparticle self‐assemblies. Because of their well‐defined molecular compositions, enhanced stability, and diverse surface functionalities, nanoclusters offer an excellent platform for developing colloidal superstructures via the self‐assembly driven by surface ligands and metal cores. More importantly, recent reports have also revealed the hierarchical structural complexity of several nanoclusters. In this review, the formulation and periodic self‐assembly of different noble metal nanoclusters are focused upon. Further, self‐assembly induced amplification of physicochemical properties, and their potential applications in molecular recognition, sensing, gas storage, device fabrication, bioimaging, therapeutics, and catalysis are discussed. The topics covered in this review are extensively associated with state‐of‐the‐art achievements in the field of precision noble metal nanoclusters.

Monolayer thiol-protected noble metal nanoclusters are attractive nanoscale building blocks for well-defined colloidal superstructures. However, achieving facile reversible self-assembly of nanoclusters using external stimuli is still in its infancy. Herein, we report the synthesis and photon-assisted reversible self-assembly of thiolated azobenzene-stapled Au25 nanoclusters. Photoactivation of functionalized nanoclusters in dichloromethane by irradiating ultraviolet light at 345 nm resulted in a visual change and formation of disc-like colloidal superstructures (d ~100 -1000 nm). The superstructures readily disassembled into individual nanoclusters upon irradiating with the visible light at 435 nm. Systematic changes in both the electronic absorption bands and nuclear magnetic resonance spectra of chromophores in solution suggest that the self-assembly is driven by the photoisomerization of surface ligands. High-resolution transmission electron microscopy, electron tomographic reconstruction, dynamic light scattering, and small-angle X-ray powder diffraction show that the disc-like superstructures contain densely packed nanoclusters. Long-range self-assembly and disassembly under ultraviolet and visible light, respectively demonstrate reversible photo-switching in nanoclusters.NCs). Dried [Au25(C3-AMT)18] -NCs were stored at 4 ºC for further characterizations. ASSOCIATED CONTENT Supporting InformationThe Supporting Information is available free of charge on the ACS Publications website. Scheme S1, S2 and Figures S1-S17 as described in the text (PDF) Video S1 as described in the text (MOV)