Impact of Counterions on the Electronic Structure and Optical Properties of Water-Soluble Au₂₅ Clusters

Ligand-stabilized gold nanoclusters have raised significant interest due to great advances in their atom-precise design for a range of functionalities for catalysis, optoelectronic applications, bioimaging, and nanomedicine. Theory and computational investigations can greatly help to understand the effects from clusters' environment to their electronic structure and optical excitations. Here, we have performed a systematic density functional theory study on the impact of large counterions on the electronic structure of small water-soluble gold (Au₂₅) clusters. We show that counterions not only stabilize cluster isomers as previously shown [Chem 2021, 7, 2227-2244] but also modulate excitation energies and redistribute oscillator and rotatory strengths among dipole-allowed transitions, significantly altering the photophysical behavior of the nanoclusters. These findings help to understand the photophysics of clusters in realistic solution-phase conditions advancing further design efforts for applications.