Sensitive luminescent chemosensing of fluoride based on Eu-doped Zn-LMOF in aqueous media: structural and spectroscopic studies

Selective anion sensing/recognition by luminescent compounds able to operate in aqueous media is a central topic of supramolecular analytical chemistry that impacts biological and environmental chemistry. In this work, a novel blue-emitting (lambda(em) = 370 nm) 3D metal-organic framework {[Zn-3(BDC)(3)(EtOH)(2)](EtOH)(0.6)}(infinity), Zn-LMOF (BDC = 1,4-benzenedicarboxylate), was synthesized and structurally analysed by single-crystal X-ray diffraction. Subsequently, an Eu(iii)-doped Zn-MOF was obtained using Zn-LMOF by a post-synthetic ball milling reaction, and this compound was studied in detail as a luminescent chemosensor for anions (e.g., halides, pseudohalides, oxyanions, and carboxylates) in 20% aqueous ethanol. The new Eu@Zn-LMOF is a hydrostable material with a long-lived pink emission originated by an efficient energy transfer from the excited energy levels of Zn-LMOF toward the D-5 state of Eu(iii) centers, as evidenced by its strong emission signals at 591, 616, 650, and 698 nm, lifetime (tau = 0.68 ms), and quantum yield (phi(PL) = 0.32). The addition of anions to aqueous ethanolic dispersions of Eu@Zn-LMOF modified their emission intensities corresponding to Eu(iii) ions, with a pronounced selectivity and quenching response (K-SV = 7.27 x 10(3) M-1) toward F- over common interfering anions such as acetate, phosphate, and heavy halides. The detection limit in the presence of potentially interfering anions is 13.70 mu mol L-1. On the basis of multiple spectroscopic tools, such as SEM-EDS analysis, the optical change is attributed to the efficient release of Eu(iii) ions from the Zn-LMOF matrix with the simultaneous formation of EuF3. These results demonstrate the usefulness of lanthanide-doped Zn-LMOFs as analytical tools for the selective quantification of a neurotoxic and environmental anion in aqueous media.