Luminescent Hydrogel Based on Silver Nanocluster/Malic Acid and Its Composite Film for Highly Sensitive Detection of Fe3.

Metal nanoclusters (NCs) with excellent photoluminescence properties are an emerging functional material that have rich physical and chemical properties and broad application prospects. However, it is a challenging problem to construct such materials into complex ordered aggregates and cause aggregation-induced emission (AIE). In this article, we use the supramolecular self-assembly strategy to regulate a water-soluble, atomically precise Ag NCs (NH4)9[Ag9(C7H4SO2)9] (Ag9-NCs, [Ag9(mba)9], H2mba = 2-mercaptobenzoic acid) and L-malic acid (L-MA) to form a phosphorescent hydrogel with stable and bright luminescence, which is ascribed to AIE phenomenon. In this process, the AIE of Ag9-NCs could be attributed to the non-covalent interactions between L-MA and Ag9-NCs, which restrict the intramolecular vibration and rotation of ligands on the periphery of Ag9-NCs, thus inhibiting the ligand-related, non-radiative excited state relaxation and promoting radiation energy transfer. In addition, the fluorescent Ag9-NCs/L-MA xerogel was introduced into polymethylmethacrylate (PMMA) to form an excellently fluorescent film for sensing of Fe3+. Ag9-NCs/L-MA/PMMA film exhibits an excellent ability to recognize Fe3+ ion with high selectivity and a low detection limit of 0.3 μM. This research enriches self-assembly system for enhancing the AIE of metal NCs, and the prepared hybrid films will become good candidates for optical materials.