Photoluminescence control by atomically precise surface metallization of C-centered hexagold(I) clusters using N-heterocyclic carbenes

The properties of metal clusters are highly dependent on their molecular surface structure. The aim of this study is to precisely metallize and rationally control the photoluminescence properties of a carbon(C)-centered hexagold(I) cluster (CAu6I) using N-heterocyclic carbene (NHC) ligands with one pyridyl, or one or two picolyl pendants and a specific number of silver(I) ions at the cluster surface. The results suggest that the photoluminescence of the clusters depends highly on both the rigidity and coverage of the surface structure. In other words, the loss of structural rigidity significantly reduces the quantum yield (QY). The QY in CH2Cl2 is 0.04 for [(C)(Au-I-BIPc)(6)AgI3(CH3CN)(3)](BF4)(5) (BIPc = N-isopropyl-N'-2-picolylbenzimidazolylidene), a significant decrease from 0.86 for [(C)(Au-I-BIPy)(6)AgI2](BF4)(4) (BIPy = -Nisopropyl-N'-2-pyridylbenzimidazolylidene). This is due to the lower structural rigidity of the ligand BIPc because it contains a methylene linker. Increasing the number of capping Ag-I ions, i.e., the coverage of the surface structure, increases the phosphorescence efficiency. The QY for [(C)(Au-I-BIPc2)(6)Ag-4(I)(CH3CN)(2)](BF4)(6) (BIPc2 = N,N'-di(2-pyridyl)benzimidazolylidene) recovers to 0.40, 10-times that of the cluster with BIPc. Further theoretical calculations confirm the roles of Ag-I and NHC in the electronic structures. This study reveals the atomic-level surface structure-property relationships of heterometallic clusters.

Automated summary

The aim of this study is to metallize and control the photoluminescence properties of a carbon-centered hexagold(I) cluster using N-heterocyclic carbene (NHC) ligands and silver(I) ions. The results show that the photoluminescence of the clusters depends on the rigidity and coverage of the surface structure. Increasing the coverage of silver(I) ions enhances the phosphorescence efficiency.