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

Luminescentlanthanide metal-organic frameworks (Ln-MOFs)draw great interest due to their promising luminescent propertiesand wide applications in sensor design. In this work, a europium-organicframework (DPQ-Eu) has been synthesized under solvothermalconditions based on the aggregation-induced emission (AIE) ligand4, 4 '-(quinoxaline-2, 3-diyl)-dibenzoic acid (H(2)DPQ). Structural analyses show that DPQ-Eu adoptsthe monoclinic C2/c space group and forms a 3, 6-connected 2D porousnetwork with a topological symbol of {4(2)center dot 6}(2){4(4)center dot 6(9)center dot 8(2)}. The formationof DPQ-Eu contributes an absolute quantum efficiencyof 21.49% compared with that of the AIE ligand H(2)DPQ (0.02%) mainly due to the coordination-induced emission,providing DPQ-Eu with a great potential of being a luminescentsensor. Fluorescent investigations show that DPQ-Eu hasa selective and sensitive response to Fe3+ and Hg2+ among various metal ions by ratiometric emission changes of thedecreased emission at 415 nm and increased emission at 676 nm, withthe detection limits of 25.99 and 39.70 nM and good reusability (5times). The sensing behaviors probably can be ascribed to the promotedantenna effect from the ligand to the Eu-(III) center by the coordinationof Fe3+/Hg2+ to the quinoxaline moiety. Foranion sensing, DPQ-Eu can respond to Cr2O7 (2-) by emission quenching at both 415 and676 nm with a detection limit of 9.88 nM and 5 times reusability,probably associated with the energy competing absorption and reducedenergy 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, probablycorresponding to the inhibition of energy transfer from the ligandto the Eu-(III) center caused by the binding interactions between theCN(-) and Eu-(III) nodes. A new dicarboxylic acid functionalizedAIE ligand has beenfacilely prepared and used for the construction of luminescent andporous Eu-MOF which can be employed as a sensitive and ratiometricsensor for Fe3+, Hg2+, Cr2O7 (2-), and CN- ions.