Synthesis and crystallization of a carboxylate functionalized N-heterocyclic carbene-based Au13 cluster with strong photo-luminescence

Abstract

Here we report the synthesis and crystallization of a –COOH-capped N-heterocyclic carbene (NHC)-protected Au₁₃ cluster. The single-crystal structure of the –COOH-capped NHC-Au₁₃ 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 Au₁₃(bi-NHC carboxyl)₅Cl₂ (hereafter abbreviated as Au₁₃-c). The density functional theory (DFT) calculations confirm that Au₁₃-c is an electronically stable eight-electron super-atom cluster and elucidate its optical transitions in the UV-Vis range. The Au₁₃-c cluster exhibits excellent thermal and chemical stability under bio-relevant conditions. Additionally, this cluster shows a strong red emission in DMF and H₂O with an excellent quantum yield (QY) of 40% and 12.6%, respectively. The high QY of Au₁₃-c enables its use in cell imaging on both cancer and noncancerous cells.