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.