Design and synthesis of a new highly efficient adjustable Ln-MOF for fluorescence sensing and information encryption

Elemental analysis, infrared spectroscopy, and X-ray single crystal diffraction indicated that a novel metal-organic framework (Tb-MOF) designated as 0.5n[H₂bpy]·[Tb(dpa)(H₂O)₂]_n·4nH₂O was synthesized successfully, (where H₄dpa = 5-(3, 4-dicarboxy- phenoxy) isophenic acid, bpy = protonated 4,4'-bipyridine). Tb-MOF adopts a 3D network structure based on Tb^III ions and the (dpa)^4- ligand through µ₄: η¹, η², η², η² binding modes. Various luminescent Eu_xTb_1-x-MOFs were prepared by adjusting Tb³⁺ and Eu³⁺ concentrations. Fluorescence analysis revealed Tb-MOF's strong fluorescence and excellent sensing ability for pollutants like nitrobenzene (NB), ornidazole (ORN), and fluridine (Flu) in water. It is worth noting that the fluorescence quenching rate of Tb-MOF for nitrobenzene can reach 97.1 %, which is also one of the highest among Ln-MOFs. XPS, LUMO orbital energy levels, fluorescence lifetime, and UV absorption were employed to explore the fluorescence quenching mechanism. Tb-MOF demonstrates robust anti-counterfeiting properties and stability, particularly against Flu, and allows rapid in situ imaging of pesticide residues on vegetables. Moreover, leveraging the adjustable emission spectra of Eu_xTb_1-x-MOF, a barcode system for anti-counterfeiting labels has been developed, showing the versatility of stable metal-organic frameworks in advanced technologies for anti-counterfeiting applications.