Enhanced Luminescence in Zn+2-Induced Au-14 Nanocluster Aggregates

Aggregation-induced emission (AIE) is an emerging strategy used for the creation of superstructures constructed by the self-assemblies of metal nanoclusters (NCs) to tune their photophysical properties. Here, we explored the AIE of D-penicillamine-capped Au-14 NCs by introducing Zn2+ ions with intriguing photophysical properties. The electrostatic interaction between the carboxylate (-COO-) groups of penicillamine ligands in the NCs with Zn2+ ions formed large cross-linked aggregated structures evident from microscopic studies. X-ray photoelectron spectroscopy corroborates the fact of charge transfer from electron-rich -COO- to Zn2+ ions. We observed the huge photoluminescence enhancement (50-fold) in the Zn-induced Au-14 NCs compared to Au-14 NCs, with a photoluminescence quantum yield enhancement from 0.56 to 4.31% due to the surface rigidification of Au-14 NCs that suppresses nonradiative relaxation. We found that pH (in the range of pH similar to 3-10) controls the photophysical properties of these aggregates. The disaggregation of Zn-induced Au-14 NCs in the presence of a chelating ligand, which can be reversed by reintroducing Zn+2 ions, further supports the coordinating mechanism of Zn+2 ions with Au-14 NCs. These nanoaggregates are used as a probe for the detection of Zn2+ ions in the linear concentration range 0.5-0.25 mu M with a limit of detection of 754 nM.