Azo-β-naphthol-salicylaldehyde conjugate: An azo dye-Schiff base hybrid as colorimetric chemosensor for highly selective and sensitive detection of Fe3+-Experimental and theoretical studies and applications

Abstract

In this work, a new azo dye-Schiff base hybrid colorimetric chemosensor NP-7 has been developed and comprehensive computational studies were undertaken to rationalize the experimental findings. Under the optimized conditions (DMF-H2O (9:1, v/v, pH = 7.4, 10 mM HEPES buffer)), NP-7 showed a spontaneous and distinct naked-eye colour change from colourless to orange with remarkable selectivity and sensitivity towards Fe3+. The binding mechanism of NP-7 and Fe3+ was proposed based on a 2:1 complex formation with the binding constant (Ka) of 1.9 × 102 M-1/2. Notably, NP-7 exhibited a detection limit of 33.6 nM for Fe3+, evidencing its sensitive colorimetric response. The NP-7-Fe3+ complex showed efficient reversibility with the competitive chelating reagent Na2EDTA, thus indicating its recyclable nature. The sensing mechanism was explained with the help of UV–Vis spectroscopic titration, Job’s plot, FTIR spectra, 1H NMR titration and Density Functional Theory (DFT) calculations. Interestingly, both 1H and 13C NMR spectra showed two solution-phase conformers of NP-7, viz. ZC(O)-NECN (∼40%) and ZC(O)-NZCN (∼60%), in contrast to a single solid-state conformer (ZC(O)-NECN) observed by single-crystal X-ray diffraction (SCXRD) method and their structures, relative stabilities and isomeric ratio were further supported by DFT calculations. NP-7 displayed its practical applicability through the selective detection and quantification of Fe3+ in spiked water samples and the construction of an INHIBIT logic gate. © 2026 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.