Rational Design of Three Two-Fold Interpenetrated Metal–Organic Frameworks: Luminescent Zn/Cd-Metal–Organic Frameworks for Detection of 2,4,6-Trinitrophenol and Nitrofurazone in the Aqueous Phase

Through a dual-ligand strategy, three mixed ligands metal–organic frameworks (MOFs), namely, {[Zn2(Py2TTz)2(BDC)2]·2(DMF)·0.5(H2O)}n (1), {[Cd2(Py2TTz)2(BDC)2]·2(DMF)}n (2), and {[Co2(Py2TTz)2(BDC)2]·2(DMF)·0.5(H2O)}n (3) (where Py2TTz = 2,5-bis(4-pyridyl)thiazolo[5,4-d]thiazole, BDC = 1,4-benzenedicarboxylate, and DMF = N,N-dimethylformamide), were synthesized under solvothermal conditions. The single-crystal X-ray diffraction analyses reveal that the three MOFs possess similar 2-fold interpenetrated three-dimensional framework structures with pcu topology. The fluorescence properties of compounds 1 and 2 were investigated systematically. The results show that compounds 1 and 2 display good fluorescent properties, which can be efficiently quenched by a trace amount of nitroaromatics 2,4,6-trinitrophenol (TNP) and antibiotics nitrofurazone (NZF) in water media. The large Ksv value and small limit of detection demonstrate that compounds 1 and 2 can serve as good fluorescent sensors for TNP and NFZ detection in an aqueous system. Density functional theory calculations and spectral overlap experiments, coupled with luminescence decay experiments, confirm that the luminescence quenching mechanism involves a dynamic and static quenching mechanism and is dominated by the photoinduced electron transfer process and the Förster resonance energy transfer process simultaneously.