A New Colorimetric Azo-azomethine Probe for Fluoride Ion Detection Based on the Proton Transfer Signaling Mode: Real-life Applications

Four novel receptors were designed and synthesized for colorimetric detection of F− ions. The introduction of four electron withdrawing groups into the backbone of the receptors makes the two phenolic groups efficient hydrogen bonding sites. The binding properties of receptors with anions were examined for the first time by UV–Vis, 1H NMR and fluorescence spectroscopies. The addition of F− resulted in a marked red shift of the charge-transfer absorbance band accompanied by a color change. The addition of other anions such as Cl−, Br−, I−, NO3−, ClO4−, CN− and HSO4− did not result in observable spectral change and solution color change. The 1H NMR titration revealed that the colorimetric response was considered to be the direct consequence of hydrogen-bond formation between the phenolic groups of the receptors and fluoride ions followed by deprotonation. The current sensory systems could as well be served as practical tool for immediate and qualitative detection of inorganic 'anions in real-life applications'.