Selective azo dye-based colorimetric chemosensor for F^-, CH₃COO^- and PO₄³

Developing anionic receptors is a huge challenge, especially those using hydrogen bonds to interact with the analytes. Azobenzene-derivative selective chemosensor has been evaluated for anion recognition properties. 2‑(4‑Hydroxiazobenzene)benzoic acid (HABA) has two hydrogens groups available for interaction; one is the phenol group and the other is the carboxylic acid group, enabling interaction with cations and anions. Subsequently titrations of chromophore 2‑(4‑hydroxiazobenzene) benzoic acid were performed with cations and anions; however, only the interactions with fluoride, acetate, and phosphate were significant. These data demonstrated the sensitivity of the ligand HABA by these anions, characterized by the displacement of the absorbance bands at 372nm to 491nm in acetonitrile. The association constants found to fluoride, acetate, and phosphate were 1.56×10⁴±0.28, 1.25×10⁴±0.60, and 1.90×10⁴±0.67mol^-1dm³ respectively. ¹H NMR titrations data confirmed association constants values in agreement with those of UV-Vis, besides showing evidence of the analyte interaction by the hydrogen-bonding of the carboxylic acid group. Overall, UV-Vis limit of detection data for fluoride (1.05×10^-7moldm^-3), acetate (3.77×10^-8moldm^-3) and phosphate (3.00×10^-8moldm^-3), support that HABA can detect low concentration of these anions.