Coumarin Based Fluorescent Probe for Colorimetric Detection of Fe and Fluorescence Turn On-Off Response of Zn and Cu.

A new coumarin based Schiff-base chemosensor-(E)-7-(((8-hydroxyquinolin-2-yl)methylene) amino)-4-methyl-2H-chromen-2-one (H L) was synthesized and evaluated as a colorimetric sensor for Fe and fluorescence "turn on-off" response of Zn and Cu using absorption and fluorescence spectroscopy. Upon treatment with Fe and Zn, 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 NMR titration as well as ESI-Mass spectral analysis. The complex solution of H L with Zn ion exhibited reversibility with EDTA and regenerate free ligand for further Zn sensing. H L exhibits two INHIBIT logic gates with two different chemical inputs (i) Zn (IN1) and Cu (IN2) and (ii) Zn (IN1) and EDTA (IN2) and the emission as output. Again, an IMPLICATION logic gate is obtained with Cu 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 L, HL-Zn and HL-Cu are 2.193, 1.834 and 0.172 eV, respectively.