Pyrazoline derivatives can be used as ligands because they have photophysical properties and can chelate metal ions which cause very strong absorption, emission and have a fluorescence properties. Therefore, in recent years, pyrazoline ligands and their derivatives have been widely used for chemosensors. This research aims to detect fluorescence-based heavy metal ions Hg2+ and Cd2+ using a metal ion complex compound Zn2+ with pyrazoline derivative ligand. The research was started by synthesizing pyrazoline-derived ligands, then synthesizing complex compounds. Complex compounds were characterized using Fourier Transform Infra Red (FTIR), UV-Vis Spectrophotometer, and Spectrofluorometer. Then, a fluorescence study was carried out to determine the type of fluorosensor for complex compounds with the addition of heavy metal ions Cd2+ and Hg2+. The last stage is UV-Vis spectroscopy study on the addition of heavy metal ions Hg2+ and Cd2+. Pyrazoline derivative ligand obtained as para-di-2-(1-phenyl-3-pyridyl-4,5-dihydro-1H-pyrazole-5-yl)benzene is a yellow solid. The metal ion complex compound Zn2+ with pyrazolin derivative ligand is a brown colored compound, has a yield of 45 % and a melting point is 245 oC. The FTIR spectrum showed the presence of functional groups such as amine, C-H aromatic, C=N, C=C aromatic, C-N, Zn-N and Zn-Cl. Analysis with UV-Vis spectrophotometer showed that there was a shift in the maximum wavelength from the ligand to the Zn(II)-ligand complex, namely 240 nm to 246 nm and 363 nm with molar absorptivity values (log ) of 4.56 and 4.28, respectively. For fluorescence analysis, two absorbance peaks were obtained, namely at a wavelength of 370 nm with an intensity of 3644 a.u and 478 m at 8216 a.u. The results of fluorescence chemosensor studies on the addition of heavy metal ions Hg2+ and Cd2+ showed that the metal ion complex compound Zn2+ with pyrazoline-derived ligands can detect heavy metal ions Hg2+ and Cd2+ with a turn-on type.
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