Synthesis and crystallization of a carboxylate functionalized N -heterocyclic carbene-based Au 13 cluster with strong photo-luminescence.

Here we report the synthesis and crystallization of a -COOH-capped N -heterocyclic carbene (NHC)-protected Au 13 cluster. The single-crystal structure of the -COOH-capped NHC-Au 13 cluster reveals a classic icosahedral core with one Au atom in its center. The icosahedral core is surrounded by five NHC ligands with pseudo C5 symmetry and exposed carboxyls in a pentagonal antiprism fashion. The detailed formula of the Au cluster was identified as Au 13 (bi-NHC carboxyl) 5 Cl 2 (hereafter abbreviated as Au 13 -c). The density functional theory (DFT) calculations confirm that Au 13 -c is an electronically stable eight-electron super-atom cluster and elucidate its optical transitions in the UV-Vis range. The Au 13 -c cluster exhibits excellent thermal and chemical stability under bio-relevant conditions. Additionally, this cluster shows a strong red emission in DMF and H 2 O with an excellent quantum yield (QY) of 40% and 12.6%, respectively. The high QY of Au 13 -c enables its use in cell imaging on both cancer and noncancerous cells.