A novel aluminum-sensitive fluorescent chemosensor based on 4-aminoantipyrine: An experimental and theoretical study

A practical and an efficient Schiff base fluorescent chemosensor, salicylidene-4-aminoantipyrinyl-4-aminophenol (A2) has been synthesized through the condensation procedure of 1-phenyl-2,3-dimethyl-4-(N-2-hydroxybenzylidene)-3-pyrazoline-5-one and 4-aminophenol. Compound A2 has displayed a considerable fluorescence enhancement with high selectivity and sensitivity toward Al³⁺ ion and exhibited an emission band at 484 nm, which contained a low detection limit (LOD) of 1.06 × 10^-7 M. In accordance to the experimental study, DFT, TDDFT calculations, and the enhancement of fluorescence intensity might be attributed to the inhibition of Photoinduced Electron Transfer (PET) along with the Excited-State Intramolecular Proton Transfer (ESIPT). As it has been specified by Job's plot and DFT calculations, the binding stoichiometries of A2 with Al³⁺ are 1:1, while the association constant (Ka) of Al³⁺ has been calculated and observed to be 2.67 × × 10⁵ M^-1. Furthermore, the binding behavior and sensing mechanism of A2 with Al³⁺ have been confirmed through the experiments of ¹H NMR titration.