A naked-eye sulfonamide-based colorimetric and fluorescent “turn-on” chemosensor for detecting fluoride

A novel sulfonamide-based chemosensor MBV ((E)-N, N-diethyl-3-((2-hydroxy-3-methoxybenzylidene)amino)-4-methoxybenzenesulfonamide) was synthesized for sensing of F⁻. MBV could detect exclusively F⁻ with both “off-on” fluorescent enhancement from colorless to orange and a color variation from colorless to yellow. Detection limit of for fluoride was determined to be 6.76 µM through fluorescence and 0.77 µM through colorimetry. Binding mode of MBV with F⁻ was determined to be a 1:1 ratio with fluorescent and UV-visible studies, ESI-MS, and NMR titration. MBV was well applied as fluorescent and colorimetric test strips for in-the-field measurements of F⁻. In addition, MBV could be reused for the dection of F⁻ with Hg(NO₃)₂. Sensing process for fluoride was suggested to be ICT mechanism via the deprotonation of a phenolic group, which was greatly illustrated by calculations.