Fabrication of a multifunctional ionic covalent organic framework via the Menshutkin reaction and ion-exchange for dual-mode detection of organochlorine pesticides and design of a smartphone sensing platform†

Abstract

The synthesis of ionic covalent organic frameworks (iCOFs) is considerably limited due to the low solubility and challenging synthesis of the required monomers, making the ionic conversion of neutral COFs via post-synthetic modification (PSM) a viable alternative. Herein, we successfully converted a neutral COF (TfaTta) into a cationic COF (TfaTta–Br) through the Menshutkin reaction, utilizing benzyl bromide (BnBr) as the halogenated hydrocarbon, which subsequently underwent ion-exchange with the anionic compound methyl blue (MB) to generate a multifunctional material (TfaTta–MB) with dual emission. Studies demonstrated that TfaTta–MB is capable of ratiometric sensing of dicamba (DMA) and 2,6-dichloro-4-nitroaniline (DCN), two commonly used organochlorine pesticides, with limits of detection as low as 0.0241 μM and 0.128 μM, respectively. Density functional theory (DFT) calculations were performed for further research on the responsive mechanism. A hydrogel film (TfaTta–MB/AG) was prepared and affixed to a laboratory glove, creating a portable sensing device for detecting pesticide residues on the surface of vegetables. Notably, the obtained material enables colorimetric sensing of DMA and a smart sensing platform has been developed leveraging this functionality. In short, this work not only broadens the scope of ion transformation methods for neutral COFs, but also imposes great improvement in ratiometric sensing for organochlorine pesticide residues.