New Eu(III) pyromellitic metal-organic framework with intense red phosphorescence for sensing of pesticides with selectivity to methyl-parathion in aqueous media. Crystal structure and spectroscopic studies

• A novel intense red-emitting 3D Eu(III) pyromellitic MOF 1 was synthesized and structurally described. • The Eu(III)-MOF 1 is a hydrostable red emitting compound with a long-lived emission originated by efficient energy transfer from ligand to metal. • The Eu(III)-MOF 1 can be effectively/selectively sense the pesticide methyl parathion in aqueous media • These results highlight the use of a luminescent Eu(III) MOF as chemosensors for low-cost and selective detection of pesticides. Methyl parathion (MP) is one of the world's most widely used organophosphate insecticides for crop protection. Due to its high toxicity to living organisms and its tendency to accumulate in the food chain, soil, and water, there is an evident need to develop potent optical chemosensors for this anthropogenic pollutant. Herein, a novel intense red-emitting 3D metal-organic framework 1 with formula [Eu 2 (btec) 1.5 (H 2 O) 8 ]∙6(H 2 O) (btec=1,2,4,5-benzenetetracarboxylate) was synthesized, structurally described by single-crystal X-ray diffraction and characterized by several analytical tools including scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD), thermal analysis (TGA), FT-IR spectroscopy, BET experiments and X-ray photoelectron spectroscopy (XPS). The Eu(III) pyromellitate-based MOF 1 is a hydrostable red emitting MOF (λ em = 615 nm) with a long-lived emission (τ= 0.46 ms) originated by an efficient energy transfer from the excited energy levels of btec ligand towards the 5 D state of Eu(III) upon excitation at 260 nm in an aqueous setting. Furthermore, 1 was studied in-depth as a luminescent sensor for a series of globally used pesticides and common environmental anions. The luminescence of 1 can be effectively/selectively quenched by organophosphate insecticide MP with a pronounced selectivity over other common pesticides including malathion and glyphosate, or interfering anions with a nanomolar limit of detection of 29 ± 1 nM. By leveraging the high affinity and selectivity of MP for 1 , the rapid quantitative detection of MP in commercial milk was achieved. Based on multiple analytical tools (MALDI-TOF mass spectrometry, 31 P NMR, FT-IR, PXRD, XPS, and lifetimes) the optical change is attributed to the efficient release of Eu(III) ions from 1 with the simultaneous formation of Eu(III)-MP complex. These results highlight the use of luminescent Eu(III)-based MOFs as chemosensors for low-cost, fast and selective detection of organophosphate insecticides.