A new dual-functional ratiometric fluorescent probe based on quinoline-triphenylamine schiff base for detecting...

A novel ratiometric fluorescence Schiff-based probe N (4-(diphenylamino)benzylidene)-8-hydroxyquinoline-2-carbohydrazide (HQ-TPA) for thorium and copper was developed. The probe HQ-TPA was synthesized through the reaction of 8-hydroxyquinoline-2-carbohydrazide with 4-(diphenylamino)benzaldehyde under Schiff base conditions, and its structure was characterized using FTIR, NMR, and mass analysis. The probe HQ-TPA shows distinct dual fluorescence emissions at 440 and 556 nm (λ_ex = 380 nm). Probe HQ-TPA exhibits excellent selectivity towards Cu²⁺ and Th⁴⁺ ions over other tested metal ions in the DMSO: H₂O (7:3, v/v) medium via a ratiometric fluorescence change. The HQ-TPA forms a 1:1 and 2:1 stoichiometry with an estimated association constant of 6.64 × 10⁴ M^-1 and 1.10 × 10⁵ M^-2, and quenching constant of 3.80 × 10^-7 and 1.49 × 10^-7 M^-1 with Cu²⁺ and Th⁴⁺ ions, respectively. The detection limit of HQ-TPA towards Cu²⁺ and Th⁴⁺ was found to be 16.79 and 39.9 nM, respectively. The binding mechanism of HQ-TPA with Cu²⁺ and Th⁴⁺ ions was thoroughly studied using FTIR, NMR, EPR, and ESI-Mass analysis in support of density functional theory-based computational calculations. Additionally, the HQ-TPA probe was used to detect Cu²⁺ and Th⁴⁺ ions in various environmental water samples in realtime.