Synthesis and Characterization of a Pyrazoline-Based Fluorescence Turn-Off Sensor for Selective Fe³⁺ Detection in...

The present research focuses on synthesizing a "turn-off" fluorescent sensor Ligand, 3-{(5R)-5-[4-(dimethylamino)phenyl]-1-phenyl-4,5-dihydro-1H-pyrazol-3-yl} phenol (PZ). The structures of the newly synthesized intermediate chalcone and ligand pyrazoline (PZ) were systematically characterized using UV-Vis, FT-IR, ¹HNMR, ¹³CNMR and ESIMS spectroscopic techniques. The fluorescence and absorbance behaviour were studied by introducing heavy metal ions Fe³⁺, Al³⁺, Co²⁺, Fe²⁺, Mg²⁺, Cu²⁺, Zn²⁺, Hg²⁺, Cd²⁺, Pb²⁺, Na⁺, Ca²⁺, Sn²⁺, Ba²⁺ & Ni²⁺ among which Fe³⁺ showed the most significant quenching effect. Under optimal circumstances, the fluorescence intensity of the PZ sensor was quenched by Fe³⁺ within the range of 0 to 5 µM, exhibiting a detection Limit of 0.30 µM and a Limit of quantification of 1.004 µM. The fluorescent titration indicated the formation of a 1:1 PY-Fe³⁺ metal ion complex. The binding constant of PZ with Fe³⁺ has been calculated using modified Benesi-Hildebrand plot, which has demonstrated a higher association constant at 1.25 × 10³ M^-1. DFT calculations were performed to further investigate the formation of PZ-Fe³⁺ complex.