This study is led by Prof. Zang (College of Chemistry, Zhengzhou University), and the research team reports 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.
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 (AunAg13-n) by doping different amounts of gold atoms, which was also demonstrated by mass spectrometry (see the spectra below, A). Promisingly, their emission wavelength (see the spectra below, C) 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 of 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.
