A new hydrazone linkage-based covalent organic framework for ratiometric fluorescent probe detection of hypochlorite.

A new hydrazone-linked covalent organic framework (TFTH-COF) was synthesized and characterized. TFTH-COF has porous crystalline framework structure with high thermal stability. TFTH-COF exhibited highly selective fluorescence blue-shift response towards hypochlorite (ClO) in ethanol and accompanied by the obvious color change under both day light and UV light. TFTH-COF has the ratiometric fluorescence sensing ability for hypochlorite with high sensitivity. The ratiometric fluorescence intensity of TFTH-COF presented a linear change against hypochlorite concentration with a low detection limit of 0.417 μM. The results of XPS, FT-IR and fluorescence lifetime indicated the formation of hydrogen bond between the O and N atoms of hydroxyl and amine of TFTH-COF with hypochlorite. The DFT calculation further confirmed the formation of hydrogen bond and resulted in the change of fluorescence spectra. Its practical application ability was confirmed by good recovery rate of TFTH-COF in the quantitative detection of hypochlorite in 84 disinfectants and water samples. Moreover, TFTH-COF can also identify hypochlorite through fluorescent test strips by the naked eye. This work sheds light on the fabrication of COFs as ratiometric fluorescence probes for easily-operable, instantaneous and accurate detection and identification of different analytes.