Di- and Triphosphate Recognition and Sensing with Mono- and Dinuclear Fluorescent Zinc(II) Complexes: Clues for the Design of Selective Chemosensors for Anions in Aqueous Media.

The synthesis of a new ligand (L1) containing two 1,4,7-triazacyclononane ([9]aneN ) moieties linked by a 4,5-dimethylenacridine unit is reported. The binding and fluorescence sensing properties toward Cu , Zn , Cd , and Pb of L1 and receptor L2, composed of two [9]aneN macrocycles bridged by a 6,6''-dimethylen-2,2':6',2''-terpyridine unit, have been studied by coupling potentiometric, UV/Vis absorption, and emission measurements in aqueous media. Both receptors can selectively detect Zn thanks to fluorescence emission enhancement upon metal binding. The analysis of the binding and sensing properties of the Zn complexes toward inorganic anions revealed that the dinuclear Zn complex of L1 selectively binds and senses the triphosphate anion (TP), whereas the mononuclear Zn complex of L2 displays selective recognition of diphosphate (DP). Binding of TP or DP induces emission quenching of the Zn complexes with L1 and L2, respectively. These results are exploited to discuss the role played by pH, number of coordinated metal cations, and binding ability of the bridging units in metal and/or anion coordination and sensing.