Organic-Inorganic Molecular Nano-Sensors: A Bis-Dansylated Tweezer-Like Fluoroionophore Integrating a Polyoxometalate Core

Functionalization of the bis-lacunary Keggin polyoxotungstate [γ-SiW10O36]8– has been achieved with a two-step synthesis, by the covalent attachment of a 3-aminopropylsilane spacer and further linkage of the dansyl (5-dimethylamino-1-naphthalenesulfonyl-) residue. The resulting bis-decorated molecular hybrid [{{(CH3)2N}C10H6SO2NH(CH2)3Si}2O(γ-SiW10O36)]4– has been isolated and characterized in solution and in the solid state by FTIR, multinuclear NMR, ESI-MS, UV/Vis, luminescence spectroscopy, dynamic light scattering (DLS), and Scanning Electron Microscopy (SEM). The inorganic polyoxometalate provides a molecular nano-surface where the dansyl fluorophores are anchored with a tweezer-type arrangement. The merging of the organic and inorganic domains of the bis-dansylated complex dictates its fluorescence features, which are observed in the range 375–600 nm, its amphiphilic properties, and the multi-site recognition/signaling of cationic analytes due to the complementary effect of the tungsten oxide polyanionic surface. Indeed, the interplay of the appended sulfonamide moieties and of the molecular metal oxide fosters an enhanced selectivity for Cu2+ and Pb2+ ion sensing, even in the presence of potentially interfering cations such as Co2+. These latter are preferentially captured by the inorganic platform. By virtue of its hybrid nature, the title fluoroionophore evolves to supramolecular architectures and extended systems in mixed organic solvent/aqueous environment, yielding spherical vesicles and macroporous thin films. Flat polymeric membranes incorporating the hybrid fluorophore can also be obtained, suggesting the generation of heterogeneous sensing devices that integrate both filtration and separation functionalities.