Exploring the Structural, Optical, and electrochemical behavior of semicarbazone pyranoquinoline ligand (PQMHC) and its Cu(II) complex for efficient hydrogen peroxide sensing.

The structural, morphological, and optical features of a newly synthesized PQMHC ligand and its Cu(II)-coordinated complex were thoroughly investigated using powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and UV-Vis diffuse reflectance spectroscopy. XRD results confirmed that the PQMHC ligand crystallizes in an orthorhombic phase (space group Imma), while the Cu(II)-PQMHC complex exhibits a monoclinic phase (space group P2₁/m), indicating successful coordination with the metal center. FE-SEM images showed vertically aligned nanofibers, with average diameters of approximately 73 nm for the ligand and 52 nm for the complex, supporting their potential in optoelectronic applications. Diffuse-reflectance UV-Vis spectroscopy coupled with Kubelka-Munk/Tauc analysis yielded optical band gaps of (2.661 and 2.460 eV in the direct transition case) and (2.305 and 1.896 eV in the indirect transition case) for PQMHC and Cu(II)-PQMHC, respectively, consistent with charge-transfer-mediated gap narrowing upon complexation. The electrochemical properties of the PQMHC ligand and its Cu(II)-PQMHC complex were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Both the ligand and its Cu(II) complex demonstrated efficient electron transfer and rapid, linear sensitivity toward hydrogen peroxide detection within the 0.05-1000 µM range and a detection limit of 0.009 µM using the chronoamperometric (CA) technique. These enhanced electrochemical characteristics suggest their potential suitability for applications in sensors and biosensors.