A novel polydentate Schiff-base derivative developed for multi-wavelength colorimetric differentiation of trace Fe2+ from Fe3+
A novel Schiff-base derivative containing polydentate ligands, N-2′-hydroxyl-1′-naphthyl methylene-3-hydroxyl-2-amino pyridine (NNAP), was identified and developed. After its structure was characterized by FTIR, 1H NMR, mass spectra and element analyses, it was noted that NNAP displayed multi-wavelength colorimetric responses to Fe2+ and Fe3+, accompanied by differentiable color changes, i.e., from yellow to brown in the presence of Fe2+ but to colorless upon addition of Fe3+. Importantly, the multi-wavelength colorimetric responses to trace Fe2+ and Fe3+, i.e., at 522 nm, 448 nm and 389 nm for Fe2+ detection, and at 448 nm and 389 nm for Fe3+ detection, could efficiently eliminate system error. Their different action mechanisms, a 1 : 1 complex mode for NNAP–Fe2+ and 1 : 2 for NNAP–Fe3+, were proposed and confirmed by means of a Job's plot and theoretical calculation. NNAP would be a practical probe for multi-wavelength colorimetric differentiation of trace Fe2+ from Fe3+.