DOI: https://doi.org/10.55373/mjchem.v28i5.147

Keywords: Chromone hydrazone-based, Pb²⁺ ion, turn-on fluorescence, HOMO–LUMO transition

Abstract

The detection of Pb²⁺ 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 Pb²⁺ ions were examined using a fluorescence spectrophotometer. Only DCFCMSH exhibited turn-on fluorescence, changing from silent quenching to a green glow upon Pb²⁺ ion coordination. The DCFCMSH sensor exhibited a binding constant of 1.17 × 10⁴ M^-1 and a limit of detection (LOD) of 2.4 × 10^-8 M, demonstrating its sensitivity toward Pb²⁺ 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 Pb²⁺ 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 Pb²⁺ ion chemosensors in aqueous environments. Overall, the proposed coordination through ONO donor sites is associated with a chelation-enhanced fluorescence (CHEF) effect, and these findings highlight the potential of DCFCMSH as fluorescent chemosensors for Pb²⁺ ion detection.