Fluorescence Quenching-Based Detection of Aluminum(III): A Water-Compatible Schiff Base Sensor Approach

An off-type fluorescent Schiff base sensor S1, 6,6'-(1Z,1'Z)-hydrazine-1,2-diylidenebis(methaneylylidene)bis(3-(diethylamino)phenol), was synthesized and characterized for the selective sensing of Al(III) metal ion in aqueous medium. Sensor S1 exhibits distinct naked-eye colorimetric changes from yellow to bright orange with a bathochromic shift from 415 to 486 nm upon the addition of Al(III), corresponding to a 71 nm red shift in UV-Vis spectra. Moreover, fluorescence titration experiments in CH₃CN:H₂O (9:1, v/v) demonstrated that S1 functions as a selective and sensitive "off"-type probe for Al(III) ions under near-neutral aqueous conditions (pH 7-8) with a quenching efficiency of 82.5%. The sensor can detect Al(III) in water with the limit of detection (LOD) of 3.26 × 10^-7 M with binding stoichiometry 1:1, supported by Job's plot, Benesi-Hildebrand, Stern-Volmer plot, and HRMS data, and binding constant (K_a) of 6.10 × 10⁴ M^-1 and a Stern-Volmer constant (K_SV) of 4.82 × 10⁶ M^-1, further indicating its strong affinity. This approach also exhibit significant implementation of Al(III) sensing in real samples including the ground water and tap water.