Two Schiff-base fluorescent-colorimetric probes based on naphthaldehyde and aminobenzoic acid for selective detection of Al3+, Fe3+ and Cu2+ ions

Abstract

Two Schiff base fluorescent-colorimetric probes, 4-(1-naphthalene-methylene amino) benzoic acid (La) and 3-hydroxyl-4-(1-naphthalene-methylene amino) benzoic acid (Lb), were designed, synthesized and characterized by infrared spectra (IR), mass spectra, proton nuclear magnetic resonance (1H NMR) and carbon nuclear magnetic resonance (13C NMR). Both La and Lb can be used as fluorescent probes to detect Al3+ ions in DMF/H2O (v/v, 1:1). The detection limits were 5.4 × 10−8 M (La) and 3.3 × 10−8 M (Lb), respectively. Job's plot, mass spectra and 1H NMR titration were measured to study the bonding ratios and bonding modes. The recognition mechanisms were discussed. Furthermore, La can be used to detect Fe3+ ions and Lb can be used to detect Cu2+ and Fe3+ions through naked-eyes. The filter paper strip experiments and the ion detection in real water samples were also studied. Density functional theory (DFT) calculation was used to explain the difference of coordination ability between the two probes.