Optical properties of metal-ion-mediated Au₂₅ nanocluster-based assemblies

Building cluster assemblies from superatomic building blocks, where each cluster behaves analogously to an elemental atom, has attracted interest in the past few decades due to their enhanced optical properties. Herein, we study the optical properties of recently discovered gold nanocluster assemblies mediated by Mg²⁺, Co²⁺, Ni²⁺ and Cu²⁺ metal ions [S. Kim et al., J. Am. Chem. Soc., 2025, 147(34), 30803-30808] using time-dependent density functional theory. Depending on the coordinating metal ion, the assemblies exhibited different absorption spectra with a redshift of up to 51 nm. Surprisingly, our calculations revealed that the assemblies exhibit chiroptical response, despite being assembled from achiral building blocks. The chirality emerges from the coordination complex formed between the coordinating metal ions and the clusters' ligands and is transferred to the achiral nanoclusters. These theoretical findings may motivate researchers to create enantiopure nanocluster assemblies where spin conductivity is controlled by chirality.