Discovery of icosahedral superatomic cluster Ag₁₃ and its analogs Au₁₃

Researchers report on the first icosahedral superatomic silver nanoclusters Ag₁₃ and its analogs Au₁₃. The changes in optical properties during the evolution of Ag₁₃ to Au₁₃ are studied, and the differences in the origin of their optical properties are revealed through transient spectra and theoretical calculations. This study is led by Prof. Zang (College of Chemistry, Zhengzhou University).

In constructing metal nanoclusters using polydentate phosphine ligands with strong rigidity and chelating ability, they captured an icosahedral superatomic silver nanocluster Ag₁₃, which is usually found in the kernel of silver nanoclusters, and this is the first time it has been found to exist as an intact silver nanocluster.

Interestingly, the Ag₁₃ cluster has bright red luminescence in the solid state, while its liquid is nonemissive, “which is typical of aggregation-induced emission,” Prof. Zang says.

Because doping gold atoms into the silver clusters can effectively regulate the clusters’ emission, researchers obtained three kinds of alloy clusters (Au_nAg_13-n) by doping different amounts of gold atoms, which was also demonstrated by mass spectrometry. Promisingly, their emission wavelength and quantum yields increase with the increase of gold content.

In order to further investigate the optical property changes caused by the complete substitution of gold atoms, researchers constructed and obtained clusters of Au₁₃, which is an analog of Ag₁₃. Theoretical calculations confirm that the emission of Ag₁₃ and Au₁₃ originates from locally excited states respectively, while the luminescence of alloy clusters originates from locally excited states and charge transfer states.

At the same time, based on the bright red luminescence of Au₁₃, the coating of Au₁₃ with an amphiphilic polymer ensures that the structure and properties are not damaged, and successfully achieves low-toxicity and high-quality biological imaging. This expands the functional application prospect of luminescent gold nanoclusters in the biological field.

This study not only fills the gap between icosahedral superatomic silver nanoclusters, but more importantly, constructs a new pair of metal nanocluster analogs that can study the optical properties of clusters caused by the difference of metal species at the atomic level. This study provides a new model and mechanism for the luminescence regulation of metal nanoclusters.