Gold nanoclusters are an emerging class of atomically-precise materials whose geometric and electronic properties are readily tunable with discrete changes in composition, ligand architecture, local environment, and stereochemistry. Compared to geometric structure, establishing synthetic design rules for chemically controlling <i>electronic</i> structure has remained elusive due to the lack of a suitable sensitive and selective probe. Common approaches to measuring UV-Vis absorption spectra often obfuscate spectral features via thermal broadening and heterogeneity effects. To overcome such experimental limitations, we have turned to variable-temperature mass-selective photodissociation spectroscopy. Using triphenylphosphine-protected gold nanoclusters as a model system, our technique enables us to determine the effect of cluster composition, ligand para-substituent, and solvation environment over the energies of intracore metal-metal and metal-to-ligand charge transfer (MLCT) bands with greater detail than condensed-phase measurements. We have determined that ligand chemistry establishes the foundational electronic structure of the nanocluster, with ligand-based correlations suggesting that electronic coupling between the metal core and ligand shell can be rationally tuned by ~100 – 300 meV. Composition is equally as effective in modulating metal-metal transitions (~100 – 300 meV) as the geometric core structure reorganizes upon changes in ligand or metal-atom count. Further, the combination of ligand and core chemistry allow us to experimentally differentiate between intracore and MLCT transitions. Surprisingly, we also observe that even weakly-interacting solvents (e.g., He vs. N<sub>2</sub>) are capable of inducing ~10 – 50 meV solvatochromic peak shifts.

Chemical control over the electronic structure of discrete gold nanoclusters: Effects of composition, ligand, and solvent environment

2019 Fall National Meeting

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