Theoretical Modelling of NLO‐Active 4DMAPBP Crystal: Structure–Electronic Interplay and Optical Nonlinearity

ABSTRACT Amid the evolving landscape of nonlinear optical (NLO) materials, crystal research has gained significant attention due to the modulation in frequency generation for photonics and bio‐photonics. In this study, a new third‐order NLO material, 4‐dimethylaminopyridinium p‐bromophenolate (4DMAPBP), is investigated through comprehensive quantum chemical analysis to advance knowledge of structural, electronic, spectroscopic, and NLO properties. Density Functional Theory represents a methodological framework employed for the optimization of molecular geometry as well as the examination of fundamental electronic and optical characteristics. Analyses of Natural Bond Orbital (NBO), Hirshfeld Surface, HOMO–LUMO and Molecular Electrostatic Potential (MEP) reveal molecular stability and reactivity details. The computed first hyperpolarizability of 4DMAPBP measures 6.627 × 10 − 3 0 esu, approximately 34 times greater than urea's hyperpolarizability value. The structure‐property relationship reveals itself through detailed comparisons of nonlinear behavior between structurally similar molecules and 4DMAPBP. These findings of the 4DMAPBP molecule establish the next generation of advanced nonlinear optical systems.