A squaramide-based anionic hydrogen-bonded organic framework: enhancing sensing performance for pesticides by post-metallization with in situ imaging

Abstract

An anionic hydrogen-bonded organic framework (HOF) (named DBDA) is formed by the solvothermal reaction of squaramide-based tetracarboxylic acid organic building units (OBUs). Thanks to the diketone uncoordinated units in the squaramide functionalized groups and anionic frameworks of DBDA, Eu³⁺-functionalized HOF hybrid materials (named Eu@DBDA) were successfully fabricated and characterized. After post-synthetic modification (PSM), the synthesized hybrid materials retain the advantages of both lanthanide ions and DBDA to exhibit dual-emission luminescence properties. Therefore, we designed Eu@DBDA as a fluorescence sensor and attempted to utilize it to detect 2,6-dichloro-4-nitroaniline (DCN). It was found that the synthesized Eu@DBDA could rapidly detect DCN through luminescence quenching upon Eu³⁺-based emission, and its limit of detection (LOD) for DCN can reach 0.13 μM. Compared to the mother HOF materials, the sensing performance of DCN has been greatly improved. Furthermore, Eu@DBDA was employed to imitate fast and in situ imaging in the detection of pesticide residues in fresh produce nondestructively. This novel design approach for improving the detection performance provides a good way to prepare sensing materials related to HOFs.