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

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 & mu;M. 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.