New carbazole-based Schiff base: Colorimetric chemosensor for Fe3+ and fluorescent turn-on chemosensor for Fe3+ and Cr3+

Two novel carbazole-based Schiff-bases L1 and L2 have been synthesized and characterized by 1H NMR, 13C NMR, FT-IR spectroscopy and elemental analysis. L1 can selectively detect Fe3+ by UV-vis spectroscopy and Fe3+/Cr3+ by fluorescent spectroscopy in CH3CN among various metal ions. The addition of Fe3+ ions to a L1 solution results in a significant blue-shift from 410 nm to 378 nm accompanied with color change from yellowish green to colorless. Upon excitation at 380 nm, the addition of Fe3+ or Cr3+ causes a 13-fold or 11-fold fluorescence enhancement. The binding stoichiometry ratio of L1-Fe3+ and L1-Cr3+ is recognized as 2:1 by the method of Job׳s plot, and the possible binding mode of the system also proposes. The results indicate that L1 is an ideal chemosensor for Fe3+ and Cr3+ recognition. However, L2 without hydroxyl in ortho imino group cannot selectively recognize the tasted metal ions, indicating that the introduction of the appropriate coordination binding site to receptor can improve efficiently the selectivity of chemosensor.