The synthesis of novel salicylaldehyde imine derivatives containing pyridinium and selective detection for fluoride and cyanide in organic-aqueous media

Two new colorimetric receptors 1 and 2 nitrophenyl as signaling units and imine moieties as binding sites, were synthesized via a simple condensation reaction and characterized by 1H NMR, 13C NMR, FTIR and HRMS. The colorimetric sensing properties of the receptors toward various anions were studied using naked eye detection, UV-vis spectroscopy and 1H NMR titration. The results show that receptors 1 and 2 exhibit good UV-Vis recognition capabilities for F−, Ac− and CN−, and can recognize CN− with the naked-eye in a H2O/DMSO (3:7, V/V) solution. The detection limit for CN⁻ recognition by receptors 1 and 2 was as low as 1.31 μmol, and we prepared test papers for detecting anions using these receptors. The Job's plot analysis demonstrates a 1:1 stoichiometric binding ratio between F− and the receptors. The recognition mechanism of CN− was inferred using UV-vis and 1H NMR titrations, HRMS and theoretical calculations. Such stripes can serve as a practicable colorimetric probe for the detection of ions in many fields and avoid more expensive equipment.