Qualitative and quantitative approach towards the molecular understanding of structural, vibrational and optical features of urea ninhydrin monohydrate

Abstract

In this study, single crystals of urea ninhydrin monohydrate (UNMH) have been grown by slow evaporation method. The grown crystals were characterized by FT-IR, FT-Raman and UV-Vis-NIR spectroscopies. The Kurtz and Perry powder method was employed to confirm the near-zero SHG efficiency of the as-grown centrosymmetric UNMH crystal. The third order nonlinearity of the crystal has been studied by the open aperture Z-scan method. The nonlinear absorption coefficient is calculated and the potentiality of UNMH in optical limiting applications is identified. The molecular geometry and the origin of optical nonlinearity at the molecular level have been investigated by the density functional theory. The normal coordinate analysis was carried out to assign the molecular vibrational modes. Vibrational spectral studies confirms the presence of weak O-H•••O and moderate O-H•••O type hydrogen bonds in the molecule as well as O-H•••O, N-H•••O and blue-shifted C-H•••O type H-bonds in the crystal. The intramolecular charge transfer interactions and the electronic absorption mechanisms have been discussed. The static and the dynamic values of hyperpolarizabilities for UNMH were estimated theoretically by DFT methods.