Highly crystalline covalent organic frameworks for ratiometric fluorescent sensing of trace water in honey and N2 gas

The detection of trace water (H2O) content is important and challenging in food and food-related industries. Herein, highly crystalline two-dimensional covalent organic frameworks (TAPT-BTCA-COF) with yellow-green fluorescence were prepared by using 1,3,5-tris(4-aminophenyl)triazine (TAPT) and 1,3,5-benzenetricarboxaldehyde (BTCA) as precursors. The fluorescence of TAPT-BTCA-COF is sensitive to the solvent polarity due to the intermolecular charge transfer (ICT) effect and can be quenched by trace H2O due to the block of ICT effect by H2O. On this base, TAPT-BTCA-COF is applied for sensing of trace H2O in common organic solvents such as DMF, acetonitrile, THF and acetone with fast response and high sensitivity. The limits of detection for H2O in DMF, acetonitrile, THF and acetone are 0.082 wt%, 0.0053 wt%, 0.0091 wt% and 0.0061 wt%, respectively. Furthermore, a ratiometric fluorescent sensor is proposed by using TAPT-BTCA-COF as the signal probe and red fluorescent tris(2,2′-bipyridyl)ruthenium(II) dichloride as the reference and successfully applied for quantitatively and semi-quantitatively sensing of trace H2O in honey sample and the moisture in N2 gas.