Molecular structure and vibrational spectral investigation of charge transfer NLO crystal Naphthalene Picrate for THz application

Molecular structure and the vibrational spectra of Naphthalene Picrate have been calculated using density functional theoretical computation and compared with the experimental. The dipole moments (μ), polarizability (α), first hyperpolarizabilities (β) second hyperpolarizability (γ) and frontier molecular orbital energies are computed at the DFT level. The frontier molecular orbital calculation shows the inverse relationship of HOMO–LUMO gap with the total static hyperpolarizability. The hyperpolarizability value reveals that these classes of organic compounds show very large non-linear optical properties. Natural Bond Orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction. Terahertz time-domain spectroscopy has been used to detect the absorption spectra in the frequency range from 0.2 to 1.5 THz.

Graphical abstractStructural investigations of Naphthalene Picrate have been performed using vibrational spectra. The dipole moments (μ), polarizability (α), first hyperpolarizabilities (β) second hyperpolarizability (γ) and frontier molecular orbital energies are computed at the DFT level. The hyperpolarizability value reveals that these classes of organic compounds show very large non-linear optical properties. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction. The terahertz absorption spectra have been detected from 0.02 to 1.5 THz region and the observed peaks shows the terahertz generation is due to the intermolecular phonon modes..Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Structural features of NLO crystal NP and vibrational spectral investigation are carried out. ► The calculated first order hyperpolarizability of NP was found to be 20 times that of urea. ► Hydrogen bonding and charge transfer interactions are also analyzed. ► Observed THz peaks shows the intermolecular phonon modes and the torsion modes.