Novel 2,1,3-benzothiadiazole derivatives used as selective fluorescent and colorimetric sensors for fluoride ion

Two novel 2,1,3-benzothiadiazole derivatives, used as colorimetric and fluorescent sensors for fluoride ion were designed, synthesized and characterized. These sensors contained single hydrogen-bond functional groups, which acted as interacting sites for fluoride ion. Both sensors displayed a red color in dimethyl sulfoxide solution. Binding studies revealed that they showed noticeable colorimetric and fluorescent responses only to F− among the eight anions tested (F−, Cl−, Br−, I−, AcO−, H2PO4−, HSO4− and NO3−). 1H NMR titration proved that the interaction between compounds and fluoride ion: hydrogen bond at low fluoride ion concentration, deprotonation at high fluoride ion concentration. Moreover, those compounds showed high sensitivity and selectivity for fluoride ion by inhibiting the excited state intramolecular proton transfer processes, and the detective processes could be followed by direct visual observation.