Chromogenic and fluorogenic “off–on–off” chemosensor for selective and sensitive detection of aluminum (Al3+) and bifluoride (HF2−) ions in solution and in living Hep G2 cells: synthesis, experimental and theoretical studies

Abstract

A simple pyridine-dicarbohydrazide based colorimetric and fluorometric chemosensor L was designed and synthesized for Al³⁺ ion sensing in organo aqueous solution. In the presence of Al³⁺ ions, probe L exhibited visible color changes and fluorescence enhancement (20-fold) due to Al³⁺ induced chelation-enhanced fluorescence (CHEF) effects. Chemosensor L revealed high selectivity toward Al³⁺ ions by “turn-on” fluorescence among the other competitive metal ions examined with a detection limit of 0.8 μM. Probe L was found to bind with Al³⁺ ions in a 1 : 2 (probe : metal) stoichiometric fashion, with an association constant (K_a) of 4.26 × 10⁴ M⁻². In addition, DFT and TDDFT calculations were carried out to recognize the binding nature and electronic properties of probe L and its Al-complex. Furthermore, the in situ prepared [L–Al] complex was able to detect HF₂⁻ anions via a metal displacement strategy. The bioimaging application of Al³⁺ and HF₂⁻ was implemented in living human liver cancer cells (Hep G2).