Study on the fluorescent covalent organic framework for selective “turn-off”recognition and detection of Fe3+ ions

Covalent organic framework (TT-COF) based on 2,5-dihydroxyterephthalaldehyde and 1,3,5-tris(4-aminophenyl)benzene was prepared. TT-COF displays obvious fluorescence quenching response in ethanol towards Fe3+ with high selectivity accompanied by fluorescence red-shift. The fluorescence intensity of TT-COF at 425 nm shows a linear relationship with Fe3+ concentration with a low detection limit of 8.4 × 10−5 mol/L. The high fluorescence selectivity can be attributed to the synergetic effects of unique pore structure and the coordination of Fe3+ ions with N and O atoms of TT-COF. The coordination between TT-COF and Fe3+ ion was confirmed by reversible fluorescence change upon the addition of ethylenediaminetetraacetic acid disodium salt (EDTA), XPS spectra, and DFT calculation. The fluorescence quenching is attributed to the intramolecular charge transfer (ICT) and the absorption competition quenching (ACQ) mechanism. This work indicating the fluorescent COF as a fluorescence sensor has promising application in recognition and detection of specific metal ions.