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.