Third‐Order Nonlinear Optical Studies of 4‐Methoxybenzylammonium Nitrate (4MBAN) Using Z‐Scan Technique and the DFT Method

ABSTRACT A semi‐organic single crystal of 4‐methoxybenzylammonium nitrate (4MBAN) was successfully grown by the solvent evaporation technique at room temperature, highlighting its potential significance in nonlinear optical (NLO) applications. The third‐order NLO properties were experimentally evaluated using the Z‐scan technique at 532 nm, revealing reverse saturable absorption, self‐defocusing behavior, and an optical limiting threshold of 1.82 kJ/cm 2 . Density functional theory calculations at the B3LYP/6‐31G level were employed to optimize the molecular structure and determine key NLO parameters, including dipole moment, polarizability, and first‐ and second‐order hyperpolarizabilities. A comparative analysis with urea shows that the static second hyperpolarizability of 4MBAN is 2.16 times higher, while the dynamic second hyperpolarizabilities corresponding to the electro‐optic Kerr effect and electric‐field‐induced second harmonic generation are enhanced by 2.34 and 8.36 times, respectively. Furthermore, topological analyses, such as the Laplacian of the electron density (LED), and quantum molecular descriptors, including the average localized ionization energy (ALIE) and the local information entropy (LIE), were performed to identify reactive sites within the molecule. The combined experimental and theoretical results demonstrate that 4MBAN is a promising candidate for low‐power optical limiting applications.