Chromone Hydrazone-Based Fluorescent Chemosensor for Pb2+ Detection: Experimental and Theoretical Insights into a Turn-On Fluorescence Response

The detection of Pb 2+ ions is essential because to their extensive industrial applications and well-documented toxicity.In this study, a series of chromone hydrazone-based ligands, namely FCMSH, CFCMSH, and DCFCMSH, were synthesised under reflux conditions and characterised using CHNS elemental analysis, FTIR, NMR, and UV-Vis spectroscopy.The fluorescence properties of the ligands in the presence of Pb 2+ ions were examined using a fluorescence spectrophotometer.Only DCFCMSH exhibited turn-on fluorescence, changing from silent quenching to a green glow upon Pb 2+ ion coordination.The DCFCMSH sensor exhibited a binding constant of 1.17  10 4 M -1 and a limit of detection (LOD) of 2.4  10 -8 M, demonstrating its sensitivity toward Pb 2+ ion detection.FTIR analysis of DCFCMSH revealed shifts in the C=O (1598 cm⁻¹) and C=N (1519 cm⁻¹) bands, suggesting coordination through carbonyl and imine sites, while the appearance of the υ(SO₂) band at 1050 cm⁻¹ confirmed sulphonyl-oxygen involvement.The disappearance of the N-H proton signal (10.67 ppm) in the ¹H NMR spectrum and the C=N signal shift (147.39 ppm) in the ¹³C NMR spectrum further supported Pb 2+ ion coordination in DCFCMSH.DFT (B3LYP/6-311G(d,p)) calculations provided insights into the HOMO-LUMO transition responsible for fluorescence enhancement.Overall, coordination through ONO donor sites induces a chelation-enhanced fluorescence (CHEF) effect, and these findings represent an important step toward the development of chromone hydrazone-based as potential Pb 2+ ion chemosensors in aqueous environments.Overall, the proposed coordination through ONO donor sites is associated with a chelationenhanced fluorescence (CHEF) effect, and these findings highlight the potential of DCFCMSH as fluorescent chemosensors for Pb 2+ ion detection.