Postsynthetic Metalation Metal–Organic Framework as a Fluorescent Probe for the Ultrasensitive and Reversible Detection of PO₄^3– Ions

The self-assembly of a zinc salt with the novel ligand 4,4′,4″-[(1,3,5-triazine-2,4,6-triyl)­tris­(sulfanediyl)]­tribenzoic acid generated 3D microporous metal–organic frameworks (MOFs), namely, {[Zn₄(L^3–)₂(O^2–)­(H₂O)₂]·4EtOH}_n. The frameworks with multiple Lewis basic sites exhibit easily sensitized properties. After encapsulation of the Tb³⁺ cation in this Zn-MOF, the as-obtained fluorescent-functionalized Tb@Zn-MOFs not only maintain distinguished chemical stabilities but also exhibit strong characteristic emissions of trivalent terbium ions. Interestingly, Tb@Zn-MOF has been chosen to be a potential highly selective and sensitive luminescent platform for the reversible detection of PO₄^3– ions in aqueous and living cell buffer solutions with a fast response time of 10 s and a low detection limit (0.1 ppm). Strikingly, this work presents the first example of a fluorescent sensor that can quantitate PO₄^3– in simulated biological fluids and monitor these ions in the water system in a wide range of concentrations from 10^–6 to 10^–3 M.