Coumarin Based Fluorescent Probe for Colorimetric Detection of Fe3+ and Fluorescence Turn On-Off Response of Zn2+ and Cu2+

A new coumarin based Schiff-base chemosensor-(E)-7-(((8-hydroxyquinolin-2-yl)methylene) amino)-4-methyl-2H-chromen-2-one (H (11) L) was synthesized and evaluated as a colorimetric sensor for Fe3+ and fluorescence turn on-off response of Zn2+ and Cu2+ using absorption and fluorescence spectroscopy. Upon treatment with Fe3+ and Zn2+, the absorption intensity as well as the fluorescence emission intensity increases drastically compared to other common alkali, alkaline earth and transition metal ions, with a distinct color change which provide naked eye detection. Formation of 1:1 metal to ligand complex has been evaluated using Benesi-Hildebrand relation, Job's plot analyses, H-1 NMR titration as well as ESI-Mass spectral analysis. The complex solution of H (11) L with Zn2+ ion exhibited reversibility with EDTA and regenerate free ligand for further Zn2+ sensing. H (11) L 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 output mode. Both free ligand as well as metal-complexes was optimized using density functional theory to interpret spectral properties. The corresponding energy difference between HOMO-LUMO energy gap for H (11) L, H11L-Zn2+ and H11L-Cu2+ are 2.193, 1.834 and 0.172 eV, respectively.