Long Stability of Atomically Precise Red Emissive Copper Nanoclusters within the Gel and Their Use As a Potential Catalyst and Fluorescent Ink

Herein, an amphiphile-based hydrogel (with 5% DMF) containing natural amino acid residue has been used to prepare and stabilize red-emitting CuNCs for several months. Though different methods have been attempted, amphiphile and 4-mercaptobenzoic acid (4-MBA)-containing hydrogels are pinpointed to be the base medium to stabilize this new Cu-cluster. From a MALDI-TOF MS analysis it was found that it is a Cu₈-atom cluster stabilized by three 4-MBA ligands. Copper acetate monohydrate (Cu(CH₃COO)₂·H₂O) has been used as a copper precursor, and l-ascorbic acid has been used as a reducing agent. FEG-TEM analysis shows that the Cu cluster has an average size of 2.83 nm. Interestingly, these clusters can be used as a fluorescent ink with a visibility of the solid state under a UV-lamp with an excitation of 365 nm. This envisaged applying these CuNCs for anticounterfeiting. These Cu-clusters show an excitation of 420 nm with an emission of 620 nm, as is evident from the fluorescence spectroscopic analysis. Based on our knowledge, this is the first example of making and consequently stabilizing Cu-clusters using hydrogel as a template for a few months. Moreover, these CuNCs can also be used as a catalyst for the reduction of nitro derivatives to their amine derivatives in aqueous medium.