New trick for an old ligand! The sensing of Zn(II) using a lanthanide based ternary Yb(III)-cyclen-8-hydroxyquinoline system as a dual emissive probe for displacement assay.

A novel near-infrared (NIR) emissive lanthanide-based zinc sensor was designed, based on the self-assembly in aqueous solution between the nonemissive coordinatively unsaturated Yb(III) cyclen complex 2·Yb and the sulfonated 8-hydroxyquinoline (8-HQS) chromophore, which was employed as a sensitizing antenna. The resulting ternary complex, 2·Yb·8-HQS, displayed metal-centered emission in the NIR range upon excitation of the antenna with high quantum yield of Q = 0.23 ± 0.03% in pH 7.4 buffered aqueous solution; demonstrating efficient sensitization from 8-HQS. The addition of zinc led to quenching of the NIR emission as a result of the dissociation of the luminescent ternary 2·Yb·8-HQS complex, where the 8-HQS antenna was displaced from the Yb(III) center in favor of the formation of more stable chelates with Zn(II). These newly formed Zn(II) complexes were shown to exhibit strong green fluorescence; allowing for the simultaneous sensing of Zn(II) both within the visible and the NIR regions at physiological pH in competitive media. Furthermore, 2·Yb·8-HQS was shown to be able to detect Zn(II) with good selectivity and in a reversible manner, even in the presence of competitive group (I) and (II) metal ions as well as in the presence of several biologically important d-metal ions.