An efficient thiocarbohydrazide based fluorescencesensor S5 for the selective detection of Hg 2 + in semi-aqueous medium has been successfully designed and synthesized. The absorption (UV-Vis) and emission (fluorescence) properties of S5 were studied in various solvents. The sensor S5 displayed no distinct changes in absorption with various solvents; however some remarkable changes were noticed in fluorescence studies. Solvent dependent spectral characterization of S5 was explored via the Lippert-Mataga plot. UV-Vis and fluorescence studies also revealed that the sensor S5 could selectively detect Hg 2 + ion over the other tested metal ions. The interaction of S5 with Hg 2 + leads to colour change from colourless to yellow. The observed quenching in fluorescence intensity may be due to chelation enhanced fluorescence quenching (CHEQ). The sensing mechanism was arrived through DFT and 1 H NMR titration studies. The limit of detection was found to be 1.26 nM with a wide pH range of 4-10. Moreover, sensor S5 could demonstrate sensing efficiency for lower concentrations of Hg 2 + in real sample analysis. Its performance, as a test strip and in analysis of various water samples conferred its superior selectivity.
Experimental Details
Materials and InstrumentsUV-Vis absorption studies were carried out using the Jasco-V700 spectrophotometer. Fluorescence studies were performed with the Hitachi-V7000 spectrofluorometer. 1 H, 13 C NMR and HR-MS were recorded in Bruker Advance Varian 400 and JEOL GC Mate-II mass spectrometer repectively. Fluorescence lifetime spectra and pH measurement were performed using HORIBA Jobin Yvon. ELICO LI120 pH meter respectively. Solvents and reagents were sourced from Sigma-Aldrich and Merck Chemicals, India. The test solutions of various cations was prepared using the nitrate salts of