Bare NCs are unstable in solution, so they need to be pro-tected by ligands, e.g., thiolates, phosphines or polymers. In general,determination of the atomic structure of nanostructured materi-als is challenging because their typically heterogeneous structurespreclude crystallographic structure analysis . Recent advances in X-ray crystallography and computation.have allowed the structures of atomically precise metal NCs to beresolved . NC structure analysis with atomic res-olution provides detailed structural information about the metalcore and thiolated ligands, also known as staple motifs, around thecore, which greatly aids in understanding their unique physico-chemical properties and, specifically, the structure-luminescencerelationships of thiolated AuNCs. For example, single-crystal X-raycrystallography on phenyl-ethanethiol-coated Au25NCs revealeda central icosahedral Au13core and an exterior shell made of6 S–Au–S–Au–S staples . Later, ultrafast spec-troscopy revealed that the emission of Au25NCs at 500 nmfundamentally arises from electron-hole recombination within theAu13core with little perturbation by surface ligands, whereasnear-infrared emission at 700 nm is dependent on a passivat-ing monolayer and involves a relaxation of the core excitedstates to S–Au–S–Au–S semi-ring states .Recently, the important role of ligands in modulating the lumi-nescence of metal NCs has been addressed. Specifically, surfaceligands can modulate the luminescence of metal NCs in two dif-ferent ways: (i) charge transfer from the ligands to the metalcore via the Au S bonds, and (ii) direct donation of delocalizedelectrons from electron-rich groups of the ligands to the metalcore (Wu and Jin, 2010). Although significant progress has beenmade in elucidating the physicochemical properties of NCs, fur-ther studies are needed to obtain a profound understanding of therelation between the detailed NC structure and the luminescenceproperties.