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

ABSTRACT 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 CH 3 CN:H 2 O (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 × 10 4 M −1 and a Stern–Volmer constant (K SV ) of 4.82 × 10 6 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.