Synthesis and crystal growth of thienyl-substituted pyridinium derivatives for second-order nonlinear optics

Abstract

Two series of thienyl-substituted pyridinium salts with different counteranions have been synthesized to investigate the effect of hydrous/anhydrous phase on crystal packing. Single crystals of two kinds of salts were successfully obtained from methanol by slow evaporation method. X-Ray studies exhibited that they crystallized in the monoclinic space group P1 and P, respectively. (E)-4-(2-(5-(dimethylamino)thiophen-2-yl)vinyl)-1-methylpyridinium3-nitrobenzenesulfonate (TPNS) forms a hydrated noncentrosymmetric phase with a macroscopic optical nonlinearity 0.40 times of that of DAST at the non-resonant wavelength of λ = 2109 nm. (E)-4-(2-(5-(dimethylamino)thiophen-2-yl)vinyl)-1-methyl-pyridinium2,5-dimethylbenzenesulfonate (TPDMS) forms an anhydrous phase and crystallizes in centrosymmetric structures without SHG signal.