While the ability to crystallizemetal nanoclusters has revealed their geometric structure,t he lacko fasimilarly precise measure of their electronic structure has hampered the development of synthetic design rules to precisely engineer their electronic properties.W et rackt he evolution of highlyresolved electronic absorption spectra of gold nanoclusters with precisely mass-selected chemical composition in ac ontrolled environment. Simple derivatization of the ligands yields larger spectral changes than varying the overall atomic composition of the cluster for two clusters with similar symmetry and size.T he nominally metal-localized HOMO-LUMO transition of these nanoclusters lowers in energy linearly with increasing electron donation from the exterior of the ligand shell for both cluster sizes.V ery weak surface interactions,such as binding of He or N 2 ,yield significant statedependent shifts,i dentifying states with significant interfacial character.T hese observations demonstrate ap athway for deliberate tuning of interfacial chemistry for chemical and technological applications.

Atomically precise gold nanoclusters (AuNCs) are a class of nanomaterials valued for their electronic properties and diverse structural features. While the advent of X-ray crystallography of AuNCs has revealed their geometric structures with high precision, detailed electronic structure analysis is challenged by environmental, compositional, and thermal averaging effects present in electronic spectra of typical samples. To circumvent these challenges, we have adapted mass spectrometer-based electronic absorption spectroscopy techniques to acquire high-resolution electronic spectra of atomically precisely defined nanoclusters separated from a synthetic mixture.Here we discuss recent results using this approach to link the surface chemistry of triphenylphosphine-protected AuNCs to their electronic structure and expand on key elements of the experiment and the link between these gas-phase measurements and solution-phase behavior of AuNCs. Chemically derivatized Au 8 (P(p-X-Ph) 3 ) 7 2+ and Au 9 (P(p-X-Ph) 3 ) 8 3+ clusters, where X = −H, −CH 3 , or −OCH 3 , are used to derive systematic trends in the response of the electronic spectrum to the electron-donating character of the ligand shell. We find a linear relationship between the substituent Hammett parameter σ p and the transition energy between both sets of clusters' highest occupied and lowest unoccupied molecular orbitals, a transition that is localized in the metal core within the limits of the superatomic model. The similarity of the mass-selective and solution-phase UV/vis spectra of Au 9 (PPh 3 ) 8 3+ indicates that the interpretation of these experiments is transferable to the condensed phase. He and N 2 environments are introduced to a series of isovalent clusters as a subtle probe of discrete environmental effects over electronic structure. Strikingly, select bands in the UV/vis spectrum respond strongly to the identity of the environment, which we interpret as a state-selective indicator of interfacially relevant electronic transitions. Physically predictable trends such as these will aid in building molecular design principles necessary for the development of novel materials based on nanoclusters.

Hydride and halide ligands in gold nanoclusters exhibit an unexpected similar electronic relationship, suggesting an underlying chemical linkage between them.