Systematically Tuning the Electronic Structure of Gold Nanoclusters through Ligand Derivatization.

While the ability to crystallize metal nanoclusters has revealed their geometric structure, the lack of a similarly precise measure of their electronic structure has hampered the development of synthetic design rules to precisely engineer their electronic properties. We track the evolution of highly-resolved electronic absorption spectra of gold nanoclusters with precisely mass-selected chemical composition in a controlled 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. The 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. Very weak surface interactions, such as binding of He or N2 , yield significant state-dependent shifts, identifying states with significant interfacial character. These observations demonstrate a pathway for deliberate tuning of interfacial chemistry for chemical and technological applications.