A 2-fold interpenetrated zinc–organic framework with Lewis basic triazole sites: luminescence sensing of Fe3+ and Cr2O72−, and warm white-light emission by encapsulated Ln3+ ions

Abstract

The design and application of functional metal–organic frameworks are very important and meaningful. Herein, based on a V-shape carboxylic acid ligand, a rigid nitrogen heterocyclic ligand with a triazole group, and Zn(NO₃)₂·6H₂O, a 3D luminescent Zn-MOF [Zn₂(OBA)₂(L₁)·3DMF·4H₂O]_n (compound 1; H₂OBA = 4,4′-oxybis(benzoic acid), L₁ = 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole) with a pillared-layer structure, has been synthesized under solvothermal conditions. Two independent skeletons penetrate each other, forming a 2-fold interpenetrated structure. As an excellent chemical sensor, compound 1 can detect Fe³⁺ and Cr₂O₇²⁻ by luminescence quenching with high selectivity and sensitivity. The limits of detection of compound 1 are 0.58 μM for Fe³⁺ and 1.37 μM for Cr₂O₇²⁻, respectively. Meanwhile, compound 1 can serve as a host to encapsulate Eu³⁺/Tb³⁺ ions, realizing the tunable luminescence emission of Eu³⁺/Tb³⁺-doped samples. Furthermore, the Eu³⁺/Tb³⁺-co-doped compound 1 obtained by soaking the as-synthesized MOF into Ln³⁺ ion solution (total 25 mM; Eu³⁺ : Tb³⁺ = 2 : 3, molar ratio) exhibits white-light emission with ideal Commission International de I'Eclairage coordinates of (0.32, 0.33), a moderate correlated color temperature value of 6180 K, and an absolute quantum yield of 25.3%. These results indicate that compound 1 has promising applications in ion sensing and white-light emission.