Comprehensive density functional theory investigation of the structural, spectroscopic, and electronic properties of 5-phenoxy-1 H-benzimidazole

A detailed quantum-chemical investigation of 5-phenoxy-1 H-benzimidazole (5-PB) has been carried out using Density Functional Theory to elucidate its molecular structure, vibrational characteristics, and electronic behavior. Geometry optimization and frequency calculations were performed at the B3LYP/6-31G(d, p) level, confirming a stable ground-state configuration with no imaginary vibrational modes. The optimized structure reveals a conjugated aromatic framework in which the benzimidazole and phenoxy rings adopt a slightly twisted orientation, enabling efficient π-electron delocalization across the molecule. Simulated infrared and Raman spectra display characteristic vibrational signatures corresponding to aromatic C–H, C = N, C–N, and C–O stretching modes, supported by depolarization analysis that distinguishes symmetric and asymmetric vibrations. Time-dependent DFT calculations predict strong ultraviolet absorption dominated by π→π* electronic transitions, highlighting the conjugated nature of the molecule. Gauge-including atomic orbital (GIAO) calculations reproduce the expected deshielding patterns for heteroatoms and aromatic nuclei in the NMR spectrum. Frontier molecular orbital analysis reveals a moderate HOMO–LUMO energy gap, indicating electronic stability combined with favorable charge-transfer capability. Overall, this study provides a coherent theoretical description of 5-PB, offering valuable insight into its structural integrity, spectroscopic behavior, and electronic features, and establishes a reliable computational foundation for future chemical or biological investigations involving benzimidazole-based systems.