A luminescent covalent organic framework with recognition traps for nitro-pesticides detection, pH sensing and metal ions identification

Abstract

Special recognition sites in luminescent covalent organic frameworks (LCOFs) are extremely important to improve the selectivity of detection. Herein, we report on a novel LCOF named TFBD-Py-COF with three-in-one recognition traps composed of hydrogen bonding, reversible protonation of N and O–H⋯NC chelating unit. TFBD-Py-COF is synthesized via 3,3′,5,5′-tetraformyl-4,4′biphenyldiol (TFBD) and 4,4′,4″,4‴-(pyrene-1,3,6,8-tetrayl) tetra aniline (PyTTA), which has a two-dimensional dual rhombic pore structure based on AA stacking with the pore diameters of 0.88 and 1.38 nm. The hydroxyl group of TFBD-Py-COF can form hydrogen bonds with imines and induce the trans conformation of the mesoimine, as evidenced by the single crystal structure of the model compound. TFBD-Py-COF exhibits good chemical and thermal stability with a high BET surface area of 750 m2 g−1. TFBD-Py-COF shows visible fluorescent color from blue to green when dispersed in different organic solvents. TFBD-Py-COF has the fluorescence chemo-sensing ability for nitro-pesticides based on electron transfer-induced fluorescence quenching mechanism, allowing a high sensitivity and low detection limit of 4.0 × 10−2 ppm for p-nitroaniline. In addition, TFBD-Py-COF shows reversible acidochromic behaviors and concomitant distinct fluorescent color change due to the protonation of the imine N. Furthermore, the fluorescence of TFBD-Py-COF is selectively quenched by Fe3+ with a Ksv of 1.1 × 104 and a detection limit of 0.2 μM, owing to the coordination of Fe3+ with the O–H⋯NC chelating unit. This study demonstrates great potential of LCOFs for multifunctional detection.