Role of Anions in Inducing Noncentrosymmetry in 4-Dimethylaminopyridinium Salts for Quadratic Nonlinear Optics

A novel organic nonlinear optical material 4-dimethylaminopyridinium l-tartrate dihydrate (DMAPT·2H2O)
(C11H16N2O6·2H2O) was synthesized and characterized by CHN elemental analysis, FT-NMR, FT-IR, and FT-Raman spectral
studies. Single crystals of average dimensions 15 × 2 × 2 mm3 were grown by the solvent evaporation method from an aqueous
solution at pH 3.60 at constant temperature (30 °C). The crystal structure was solved by the single-crystal X-ray diffraction method
and belongs to the orthorhombic, noncentrosymmetric space group P212121 with unit cell dimensions of a = 7.2903(5) Å, b =
11.7980(7) Å, c = 16.2981(10) Å, and Z = 4. Thermogravimetry (TG) and differential thermal analysis (DTA) showed that the
compound decomposes at 75 °C. The optical transmittance window was found to be 310−1100 nm. The Kurtz and Perry powder
test illustrates the phase matching property of DMAPT·2H2O, and the powder second harmonic generation efficiency is 1.13 times
greater than that of KDP. The laser induced surface damage threshold for the grown crystal was measured as 9.72 GW/cm2 with a
Nd:YAG laser assembly.