Exploring crystal structure, spectral, optical, and nonlinear optical properties of hydrazide-type Schiff base through integrated experimental and computational approach
摘要
The Schiff base compound (E)-N′-(2-chlorobenzylidene)-3-methoxybenzohydrazide (OCBMAH) was synthesized via a condensation reaction and grown into high-quality single crystals using the slow solvent evaporation method. Its formation was confirmed through elemental analysis, and its molecular structure was elucidated using spectroscopic techniques. Single-crystal X-ray diffraction (SCXRD) analysis revealed a monoclinic crystal system with a centrosymmetric P21/n space group, while sharp peaks in powder X-ray diffraction (PXRD) confirmed its high crystallinity. The linear optical properties were investigated using electronic absorption and emission spectroscopy. The compound exhibits a lower cutoff wavelength at 334 nm and a direct optical bandgap of 3.36 eV, along with 90% transparency in the visible region, making it suitable for optical applications. Additionally, a violet emission peak centered at 403 nm (3.08 eV) suggests its potential for light-filtering applications. Quantum computational analysis was performed to explore the molecular structure, electronic topology, and third-order nonlinear optical (NLO) response. Theoretical geometry optimizations yielded a near-planar conformation with a root mean square standard deviation of 0.017 Å. The third-order NLO response, quantified by the average second hyperpolarizability (γ), was calculated to be 44.96 × 10⁻36 esu, indicating significant NLO activity. A comparative analysis of computational and experimental UV–Vis spectra, along with electron density difference (EDD) maps, provided insights into electronic transitions. Further investigations included density of states (DOS) and partial density of states (PDOS) analyses to assess fragment contributions. Topological studies were expanded through frontier molecular orbital (FMO) analysis, molecular electrostatic potential (MEP) maps, and localized orbital locator (LOL) analysis.