Selective ion sensing in aqueous media with ESIPT active fluorescent probes – A particular case for hypochlorite detection

We report two ESIPT active novel fluorescent probes, 1 and 2, based on benzoxazole and benzimidazole units, respectively. Their sensing aptitude towards metal ions in aqueous media is reported. A specific response of 1 to Al³⁺ and, to a lesser extent, Zn²⁺, was found, while the emission of 2 is highly impacted by the Al³⁺, Cu²⁺, Fe²⁺ and Fe³⁺ metal ions by either a blue shift or a quenching of the emission. Emission of 2 also shows a relative sensitivity to the Ni²⁺ and Hg²⁺ cations. Anions sensing studies on 2 revealed a unique emission in presence of hypochlorite ions, while glyphosate and aminomethylphosphonic acid have the effect to decrease the emission intensity by 40% and 75%, respectively. Investigations on the recognition mechanism led to the conclusion that Al³⁺ was inhibiting the ESIPT process by deprotonation of the phenol group, and that a fast but weak interaction was taking place between the hypochlorite ion and 2.