Photoluminescence and Electrochemical Sensing of Atomically Precise Cu13 Cluster

Abstract

Copper-based nanomaterials show widespread applications in the fields of luminescence and (bio)chemical sensing. Copper nanoclusters as a new class of nanomaterials have attracted extensive attention due to their atomic-level structure, but the syntheses of stable atom-precise copper clusters with good properties are still challenging. In this work, we have successfully prepared a novel mercaptoimidazole-stabilized copper(I) nanocluster: [Cu13(SR)12] NO3 (Cu13 NC, where RSH= 2-mercaptobenzimidazole) by introducing the reducing agent (NaBH4) in an acetonitrile-methanol solution of copper nitrate and RSH. The presence of NaBH4 not only reduced Cu(II) to Cu(I) but also provided a reducing system to avoid the reversed oxidation. The structure and composition of Cu13 NC have been collectively elucidated by X-ray crystallography and electrospray ionization mass spectrometry (ESI-MS). The metal framework of Cu13 NC can be seen as three triangular bipyramids sharing one or two vertices, which are surrounded by 12 thiolate ligands as protecting agents through a simple bridging mode. Since the counterions in the crystal lattice are highly disordered and could not be located, the existence of NO3- has been confirmed by infrared spectroscopy and ESI-MS. Cu13 NC exhibits good stability under ambient conditions and shows bright-red emission in the solid state (λem=627 nm). The long-life emission in the order of microseconds and large Stokes shift (≈280 nm) indicate that the luminescence of Cu13 NC is a spin-forbidden triplet phosphorescence. The absolute quantum yield of the solid-state Cu13 NC was calculated to be 1.36%. Meanwhile, there are two exposed copper atoms at each end of the structure, endowing Cu13 with good electrochemical activity. The test confirmed that Cu13 NC shows prompt response, and great selectivity in electrochemical detection of H2O2, making it a low-cost advanced H2O2 sensing material. This work provides an opportunity to investigate the structure-optical and electrochemical property relationship of copper clusters.