Preparation, properties and structures of 1-methyl-4-{2-[4-(dimethylamino)phenyl]ethenyl}pyridinium crystals with various counter anions

1-Methyl-4-{2-[4-(dimethylamino)phenyl]ethenyl}pyridinium p-toluenesulfonate (DAST) is known to be an excellent second-order nonlinear optical (NLO) crystalline material. However, studies on property variation caused by anion exchange are still an interesting subject to find out new compounds not only with large NLO properties but also with easy crystal-growing ability. In this report, some 1-methyl-4-{2-[4-(dimethylamino)phenyl]ethenyl}pyridinium derivatives with p- or m-substituted benzenesulfonate or 2-naphthalenesulfonate were prepared and their thermal properties, solubility in methanol and SHG activity were investigated. Their crystal growth was performed by the slow cooling method, and quality crystals for X-ray crystallographic analysis were obtained for three compounds. Among them, crystal structures of p-ethylbenzenesulfonate and p-styrenesulfonate derivatives were found to be almost the same as those of DAST.