Synthesis, spectroscopic and computational examination of an optically active E-N'-2,3-dimethoxybenzylidene-4-nitrobenzohydrazide crystal

Abstract

A new hydrazide derivative, (E)-N′-(2,3-dimethoxybenzylidene)-4-nitrobenzohydrazide (DB4N), was synthesized by condensation of 2,3-dimethoxybenzaldehyde with 4-nitrobenzohydrazide, and its molecular structure was confirmed by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic system, and C − N and N − N bond lengths prove the existence of extended π-electron delocalization. The crystallographic structure is stabilized by intra- and intermolecular hydrogen-bonding interactions, as revealed by Hirshfeld surface and interaction energy analyses of DB4N dimers. Experimental FTIR, FT-Raman, and UV–VIS spectra were recorded and assigned with the aid of density functional theory (DFT) calculations performed using several functionals with the 6–311++G(d,p) basis set. The optimized geometry obtained at the CAM-B3LYP level showed the best agreement with crystallographic bond lengths and angles. Natural Bond Orbital (NBO) and Quantum Theory of Atoms in Molecules (QTAIM) analyses provided detailed insight into intramolecular charge transfer, stabilization interactions, and the role of substituents in electron delocalization. The theoretically predicted vibrational wavenumbers exhibited excellent correlation with experimental values, as supported by potential energy distribution (PED) analysis. Time-dependent DFT (TD-DFT) calculations reproduced the observed absorption maxima and clarified the electronic transitions. The difference of 6 nm between the most intense experimental and theoretical bands was explained by the explicit interactions between DB4N and DMSO solvent molecules. Third-order nonlinear optical (NLO) properties were investigated using the Z-scan technique, yielding a susceptibility of χ³ = 6.554 × 10^–4 esu, indicating significant potential for DB4N in photonic and optoelectronic applications. The combined crystallographic, spectroscopic, and computational findings highlight the title molecule's stability, electronic delocalization, and promising NLO activity.