Azophenyl-substitutedSchiff Base as a Cu(II) Sensor A Molecular Spectroscopyand DFT-BasedStudy

This study investigates the physical mechanisms underlying the detection of Cu(II) using an azophenyl-substituted ortho-vanillin Schiff base (HL) probe. Its electronic and optical properties were analyzed using atomic spectroscopy and theoretical modeling. Upon interaction with Cu(II), the probe exhibits a distinct color change, confirmed through UV-Vis, FTIR, and EPR spectroscopy. The study of electronic transitions, particularly the blue shift and changes in absorption maxima, indicates a stable 1:2 stoichiometry between Cu(II) and the probe. These findings are supported by Job's plot and X-ray crystal structure analysis. Theoretical investigations based on Density Functional Theory (DFT), utilizing X-ray crystal structure data, provide detailed insights into electronic density redistribution and molecular orbital energy levels (HOMO-LUMO). During the formation of Cu(II) complexes, the observed decrease in the HOMO-LUMO gap reflects the physiochemical mechanism of electronic transitions and internal charge transfer. This process significantly alters the optical characteristics of the probe, highlighting its importance in metal ion detection and in understanding electronic charge dynamics. The HL probe demostraste significantly low cytotoxicity toward cancer cells, making it suitable for live-cell imaging of Cu(II) ions in MDA-MB 231 cellline. The probe is employed to detect cancer cells in the presence of normal cells. Its spectroscopic shifts, combined with theoretical analysis, offer a comprehensive model for studying electronic structures, energy level transitions, and molecular dynamics. This research underscores the probe’s potential not only in ion detection but also in advancing materials development and theoretical modelling for cellular and molecular processes.