Structural, spectroscopic and nonlinear optical studies on a new efficient organic donor-acceptor crystal for second harmonic generation: L-Threoninium picrate.

A new and efficient organic nonlinear optical (NLO) crystal from the amino acid family, viz., l-threoninium picrate (LTHP), has been grown by solvent evaporation technique from aqueous solution. The structure of LTHP was elucidated using single crystal X-ray diffraction data. The compound crystallized in the non-centrosymmetric space group P2(1) and the unit cell contains two l-threoninium cations and two picrate anions. The backbone conformation angles Psi(1) and Psi(2) are in cis and trans configurations for both the picrate and the threoninium residues. An intra-molecular hydrogen bond between the amine N atom and the nearby oxygen atom, viz., N1-H1B(...)O3 is observed, with a graph set motif R(1)(1)(5). The second harmonic generation (SHG) efficiency of this material was measured using Kurtz and Perry method and found to be about 43 times that of standard potassium dihydrogen phosphate (KDP) crystals. Fourier transform infrared (FTIR) and ultraviloet-visible-near infrared spectral studies were also carried out. The details are discussed.