Constructing an AIE Diphenylquinoxaline-Based Luminescent Europium-Organic Framework for Multiple Substance Sensing

Abstract

Luminescent lanthanide metal–organic frameworks (Ln-MOFs) draw great interest due to their promising luminescent properties and wide applications in sensor design. In this work, a europium-organic framework (DPQ-Eu) has been synthesized under solvothermal conditions based on the aggregation-induced emission (AIE) ligand 4, 4′-(quinoxaline-2, 3-diyl)dibenzoic acid (H2DPQ). Structural analyses show that DPQ-Eu adopts the monoclinic C2/c space group and forms a 3, 6-connected 2D porous network with a topological symbol of {42·6}2{44·69·82}. The formation of DPQ-Eu contributes an absolute quantum efficiency of 21.49% compared with that of the AIE ligand H2DPQ (0.02%) mainly due to the coordination-induced emission, providing DPQ-Eu with a great potential of being a luminescent sensor. Fluorescent investigations show that DPQ-Eu has a selective and sensitive response to Fe3+ and Hg2+ among various metal ions by ratiometric emission changes of the decreased emission at 415 nm and increased emission at 676 nm, with the detection limits of 25.99 and 39.70 nM and good reusability (5 times). The sensing behaviors probably can be ascribed to the promoted antenna effect from the ligand to the Eu(III) center by the coordination of Fe3+/Hg2+ to the quinoxaline moiety. For anion sensing, DPQ-Eu can respond to Cr2O7 2– by emission quenching at both 415 and 676 nm with a detection limit of 9.88 nM and 5 times reusability, probably associated with the energy competing absorption and reduced energy transfer from the ligand to the Eu(III) center. In addition, DPQ-Eu shows ratiometric emission changes to CN– by the emission enhancement and decrease at 415 and 676 nm, respectively, with a detection limit of 8.19 nM and five-run recycling tests, probably corresponding to the inhibition of energy transfer from the ligand to the Eu(III) center caused by the binding interactions between the CN– and Eu(III) nodes.

Pyrazine Functionalization in Eu-MOF for Exclusive Ratiometric Luminescence Sensing of PO43–

“…Interestingly, the luminescence emission of JNU-220 is 30-fold that of JNU-219, which can be mainly attributed to the boosted energy transfer from the pyrazine-functionalized linker to Eu 3+ . Luminescence titration experiments demonstrate that JNU-220 can exclusively and effectively detect PO 4 3− in aqueous solutions with a detection limit of 0.22 μM, surpassing that of the reported porous materials. The distinct color change and ratiometric luminescence behavior of JNU-220 endow it with great potential as a convenient and reliable platform for on-site realtime PO 4 3− detection.…”

“…Nutrients (e.g., phosphorus and nitrogen salts) play important roles in energy conversion, storage, and signal transduction in animals and plants. Yet, their unregulated utilization and discharge during industrial and agricultural production over the past few decades have led to the issues of water pollution, − threatening sustainable economic and social development. − As far as phosphate anion (PO 4 3– ) is concerned, it is an important component of nucleotide polyphosphates and contributes to the treatment of serious diseases, such as leukemia, myasthenia, and rickets. , However, excessive PO 4 3– would eventually be discharged into water bodies, which may accelerate the growth of algae. Notably, the enrichment of seaweed in aqueous-medium environments may result in the decrease of dissolved oxygen levels, the deterioration of water quality, and the death of aquatic organisms .…”

“…) is concerned, it is an important component of nucleotide polyphosphates and contributes to the treatment of serious diseases, such as leukemia, myasthenia, and rickets. 11,12 However, excessive PO 4 3− would eventually be discharged into water bodies, which may accelerate the growth of algae. Notably, the enrichment of seaweed in aqueous-medium environments may result in the decrease of dissolved oxygen levels, the deterioration of water quality, and the death of aquatic organisms.…”

“…13 Therefore, it is of equal importance to reinforce the management of the reasonable use of nutrients and monitor the trace nutrient residues in water bodies. 14−17 Currently, the detection of PO 4 3− is mainly accomplished by utilizing singlelayer graphene quantum dot strategies and ion-selective membrane electrodes, which are rather expensive and timeconsuming. 18,19 Hence, it is urgent to develop a facile, but highly sensitive and reliable, method for on-site real-time PO 4 3− detection.…”

“…20,36−43 Luminescence Sensing of PO 4 3− in Water. The excellent porosity, chemical stability, and luminescence properties of JNU-220 prompted us to investigate its application for sensing PO 4 3− in aqueous solutions. Luminescence titration experiments show that the intensity of the emission peak at 614 nm steadily decreases, while the emission peak at 400 nm continuously increases with the incremental addition of PO 4 3− .…”