The Colorimetric Sensor Based on Azobenzenes with Sulfonamide Group for Fluorine Ion and Moisture Detection in Organic Solvents

Abstract

Two azo dyes were prepared with mono and bis sulfonamide groups ortho diazo group respectively, 2-(4-methylbenzenesulfonamido)-2′-amino azobenzene (L1) and 2,2′-bis 4-methylbenzenesulfonamido azobenzene (L2), that recognized F− anions with color change from yellow to orange red in aprotic solvents. The quantitative detection of F− via UV absorption intensity is available, as the plot of absorbance of L2 vs F− (37.5∼150 μM) concentration showed a good linear relation in DMF solution (R2=0.9960). The low detection limit of L2 for F− is 8.74 μM. The binding mechanism of L1 and L2 with F− in aprotic solvents solvent was supposed as sulfonamide group reacted with two fluoride anions along with the deprotonating process, which has demonstrated by UV-Vis spectra, 1HNMR titration, DFT calculation and relative chemical reaction. The deprotonated (anionic) forms of L2 combined with F− are re-protonated in present of water. The L2-F have been used as colorimetric sensors exhibiting high sensitivity for water in DMSO, DMF, CH3CN, and THF with the detection limit of 0.0107 %, 0.0116 %, 0.0013 % and 0.0032 wt%, respectively.