Long Stability\nof Atomically Precise Red Emissive\nCopper Nanoclusters within the Gel and Their Use As a Potential Catalyst\nand Fluorescent Ink

Herein, an amphiphile-based hydrogel\n(with 5% DMF) containing natural\namino acid residue has been used to prepare and stabilize red-emitting\nCuNCs for several months. Though different methods have been attempted,\namphiphile and 4-mercaptobenzoic acid (4-MBA)-containing hydrogels\nare pinpointed to be the base medium to stabilize this new Cu-cluster.\nFrom a MALDI-TOF MS analysis it was found that it is a Cu<sub>8</sub>-atom cluster stabilized by three 4-MBA ligands. Copper acetate monohydrate\n(Cu(CH<sub>3</sub>COO)<sub>2</sub>·H<sub>2</sub>O) has been used\nas a copper precursor, and l-ascorbic acid has been used\nas a reducing agent. FEG-TEM analysis shows that the Cu cluster has\nan average size of 2.83 nm. Interestingly, these clusters can be used\nas a fluorescent ink with a visibility of the solid state under a\nUV-lamp with an excitation of 365 nm. This envisaged applying these\nCuNCs for anticounterfeiting. These Cu-clusters show an excitation\nof 420 nm with an emission of 620 nm, as is evident from the fluorescence\nspectroscopic analysis. Based on our knowledge, this is the first\nexample of making and consequently stabilizing Cu-clusters using hydrogel\nas a template for a few months. Moreover, these CuNCs can also be\nused as a catalyst for the reduction of nitro derivatives to their\namine derivatives in aqueous medium.