Comprehensive structural, spectroscopic, DFT, Hirshfeld surface, and nonlinear optical investigations of (E)-N′-(2,5-dimethoxybenzylidene)-4-fluorobenzohydrazide
摘要
A novel organic Schiff base, (E)-N′-(2,5-dimethoxybenzylidene)-4-fluorobenzohydrazide (EDBFB), was synthesized and systematically investigated through combined experimental and density functional theory (DFT) approaches to assess its nonlinear optical (NLO) performance. Single-crystal X-ray diffraction analysis reveals that EDBFB crystallizes in the non-centrosymmetric orthorhombic space group P212121, exhibiting a nearly planar hydrazone framework stabilized by intermolecular N–H···O hydrogen bonding interactions. Hirshfeld surface and fingerprint plot analyses indicate that crystal packing is predominantly governed by H···H (38.2%), C···H/H···C (22.9%), and H···O/O···H (16.1%) contacts. Geometry optimization using DFT reproduces the experimental structure, with bond-length deviations confined to ± 0.04 Å, and predicts a moderate HOMO–LUMO energy gap of 3.82 eV, indicating effective intramolecular charge transfer. The experimental FTIR spectrum shows excellent consistency with scaled theoretical vibrational frequencies, confirming the reliability of the computational model. UV–Vis absorption spectroscopy shows an intense π→π* transition at 252 nm, which closely matches the TD-DFT-simulated transition at 248 nm. Molecular electrostatic potential analysis reveals well-defined electrophilic and nucleophilic regions, supporting the molecule’s donor–acceptor architecture. The calculated mean polarizability (3.31 × 10− 23 esu) and first hyperpolarizability (1.675 × 10− 22 esu) values indicate a significant NLO response. Furthermore, open-aperture Z-scan studies performed at 532 nm reveal pronounced reverse saturable absorption with a nonlinear absorption coefficient of 0.92 × 10− 10 m W− 1 and an optical limiting threshold of 3.04 × 1012 W m− 2. These findings demonstrate that EDBFB is a potential candidate for optoelectronic and photonic device applications.