A highly efficient and selective coumarin based fluorescent probe for colorimetric detection of Fe3+ and fluorescence dual sensing of Zn2+ and Cu2+

Abstract

A new coumarin based Schiff-base chemosensor, (E)-7-(((8-hydroxyquinoline-2-yl)methylene)amino)-4-(trifluoromethyl)-2H-chromen-2-one (H₁₂L) was designed and synthesized. This chemosensor was evaluated as a colorimetric sensor for Fe³⁺ and fluorescence “turn on–off” response to Zn²⁺ and Cu²⁺ using steady-state absorption and fluorescence spectroscopy. In the presence of Fe³⁺ and Zn²⁺, the absorption intensity as well as the fluorescence emission intensity increases drastically compared to other surveyed metal ions, with a distinct color change which provides naked eye detection. However, in the presence of Cu²⁺, it also exhibits quenching of fluorescence emission intensity which may be due to the paramagnetic nature of Cu²⁺ ions. The stoichiometric ratio and binding constant were calculated using the Benesi–Hildebrand relation and Job's plot analyses, giving 1 : 1 stoichiometry. The interaction and binding nature of H₁₂L with Zn²⁺ ions was further confirmed by ¹H NMR titration assay and ESI-mass spectral analysis. The reversibility of H₁₂L was also studied using EDTA as a chelating ligand. Moreover, H₁₂L exhibits two INHIBIT logic gates with two different chemical inputs (i) Zn²⁺ (IN1) and Cu²⁺ (IN2) and (ii) Zn²⁺ (IN1) and EDTA (IN2) and the emission as output. Again, an IMPLICATION logic gate is obtained with Cu²⁺ and EDTA as chemical inputs and emission as the output mode. Both H₁₂L and metal-complexes were optimized using density functional theory and vibrational frequency calculations confirm that both are at local minima on the potential energy surfaces. The corresponding energy difference between the HOMOs and LUMOs of H₁₂L, Zn-complex and Cu-complex are found to be 2.11, 0.81 and 0.17 eV, respectively.