Natural bond orbital analysis, electronic structure, non-linear properties and vibrational spectral analysis of l-histidinium bromide monohydrate: A density functional theory

The spectroscopic properties of the crystallized nonlinear optical molecule l-histidinium bromide monohydrate (abbreviated as l-HBr-mh) have been recorded and analyzed by FT-IR, FT-Raman and UV techniques. The equilibrium geometry, vibrational wavenumbers and the first order hyperpolarizability of the crystal were calculated with the help of density functional theory computations. The optimized geometric bond lengths and bond angles obtained by using DFT (B3LYP/6-311++G(d,p)) show good agreement with the experimental data. The complete assignments of fundamental vibrations were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The natural bond orbital (NBO) analysis confirms the occurrence of strong intra and intermolecular N–H⋯O hydrogen bonding.

The experimental and theoretical vibrational analyses of l-histidinium bromide monohydrate have been performed. The NBO analysis explained the intramolecular hydrogen bonding and the hyperconjugative interaction.Figure optionsDownload as PowerPoint slideHighlights
► FT-Raman and FT-IR spectra of the crystallized nonlinear optical molecule l-histidinium bromide monohydrate have been recorded and analyzed.
► The assignments of the vibrational spectra have been carried out with the help of Scaled Quantum Mechanic force field theory.
► FMO, MEP and UV–vis spectra are also performed via quantum computational methods.
► The natural bond orbital analysis confirms the occurrence of strong intra and intermolecular N–H⋯O hydrogen bonding.