Synthesis, characterization (FT-IR, UV, NMR, elemental), and DFT simulations (NBO, AIM, Fukui function, MEP, FMO) of N-(4-isopropylbenzylidene)-2-phenylethanamine

Schiff bases are pivotal motifs in materials science and medicinal chemistry; their properties are governed by electronic structure. Density Functional Theory (DFT) provides a powerful framework for elucidating structure–property relationships in such systems, offering insights into reactivity, stability, and optoelectronic characteristics that are often difficult to probe experimentally. In this work, a novel phenylalanine-derived Schiff base, N-(4-isopropylbenzylidene)-2-phenylethanamine (IP), which incorporates an electron-donating isopropyl group to modulate electronic and optical properties, was synthesized and characterized. The compound is synthesized via a solvent-free mechanochemical approach and characterized using FT-IR, UV-Vis, and NMR spectroscopy, and elemental analysis. A detailed DFT study was conducted at the B3LYP/6–31G(d,p) level to optimize geometry, compute vibrational frequencies, NMR chemical shifts, electronic transitions, and global/local reactivity descriptors. Topological analysis was performed within the Quantum Theory of Atoms in Molecules (QTAIM) framework. Natural bond orbital (NBO) analysis was employed to investigate intramolecular charge transfer. The DFT-calculated spectroscopic data show excellent agreement with experimental results, validating the chosen computational model. The molecule exhibits a high HOMO–LUMO energy gap (5.112 eV), indicating significant kinetic stability. NBO analysis revealed strong hyperconjugative interactions, particularly π(C = C) → π*(C = C) delocalization within aromatic systems, with stabilization energies up to 22.59 kcal mol−1. The first hyperpolarizability (βtot = 562.71 × 10–33 esu) suggests potential nonlinear optical activity. Fukui function and Molecular Electrostatic Potential (MEP) analyses identified the imine nitrogen and specific carbon atoms as nucleophilic and electrophilic sites, respectively. This study successfully demonstrates the synergistic use of experiment and DFT to fully characterize a novel Schiff base and underscores its potential in optoelectronic and bioactive applications.