Crystal growth and characterization of the organic salt 4‐N, N‐dimethylamino‐4′‐N‐methyl‐stilbazolium tosylate (dast)

Abstract

Organic materials with large second-order nonlinear optical (NLO) susceptibilities are of interest because of their potential applications in optical signal processing and frequency conversion.['-31 Much work has therefore been devoted to the search for optimal molecular crystalline materials composed of stable chromophoric molecules with large molecular hyperpolarizabilities with an optimized orientation for large macroscopic NLO effects.Crystal growth research is of basic importance for the application of organic crystals in NLO and electro-optical devices.I4] Bulk crystalline samples of reasonable size and good quality are also essential for the accurate measurement of electro-optical and NLO coefficients in order to evaluate the potential for future applications. In addition, it has been found that, particularly in organic materials, the linear electro-optical responses are strongly dependent on the crystal quality.[" Furthermore, growth of bulk crystals of organic salts with large chromophoric cations has hardly been reported in the literature. In this work, we describe the growth of the organic salt crystal 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST), and the main results of the linear, nonlinear, and electro-optical characterization.In this crystal, the stilbazolium, one of the most efficient NLO chromophores, is the nonlinear optically active part.[61 The anion (tosylate) induces the non-centrosymmetric macroscopic crystal packing (see Fig. 2, bottom). DAST crystals have already been reported to have very large nonlinear optical su~ceptibilities.[~-~~~ The lack of reasonably large and optically homogeneous DAST crystals has hindered the accurate linear, nonlinear, and electro-optical characterization in earlier investigations of DAST.[*-'O1 DAST was synthesized by the condensation of 4-methyl-N-methyl pyridinium tosylate, which was prepared from 4-picoline and methyl toluenesulphonate, and 4-N,N-dimethylamino-benzaldehyde in the presence of pipendine (Scheme 1).DAST was then purified ( > 99.8 %) by recrystallization from water and methanol. Orange co-crystals, DAST . H20, in space group Pi (point group i, z = 2)[l2]were obtained from water or a methanol-water mixture. DAST can hardly be dissolved in non-polar and most polar solvents. Alcohol, however, is a reasonably good solvent for DAST and we found that methanol was the most suitable solvent for the growth of high-quality DAST crystals. The solubility curve for DAST in a methanol solution (see Fig. 1) was defined by saturating solutions at a high temperature and slowly cooling the solution in the presence of a precipitated solid to maintain equilibrium and analyzing the solution at defined temperatures.DAST single crystals were grown from a seeded saturated methanol solution (between 40 and 50°C with concentrations of about 4-5.5 g(DAST)/IOO g(so1vent)) by a 8 . 0 ) . I . , . , . , . , . , .

Synthesis and Crystal Growth of Stilbazolium Derivatives for Second-Order Nonlinear Optics

“…[6,7] We have studied the growth of DAST crystals, its processing, and device applications for the last several years. [8,9] The results show that DAST promises to work well for highly efficient, high-speed electrooptic applications. The growth of bulk, high-quality DAST crystals from solution, however, remains extremely difficult, requiring temperature stabilities within ±0.002 C over several months.…”

“…The most suitable solvent for crystallizing DAST is methanol. [8] DSHS and DSAS, possessing hydroxyl and amino groups, are not readily soluble, even in methanol. A higher solubility was achieved by introducing alkyl substitution, as in DSMOS and DSMAS.…”

Large‐Size Bulk and Thin‐Film Stilbazolium‐Salt Single Crystals for Nonlinear Optics and THz Generation

“…Three absorption bands observed in the infrared region at about 1.2, 1.4, and 1.7 lm correspond to overtones of the C-H stretching vibrations and have also been observed in DAST. [11] The refractive indices we have measured at the telecommunication wavelength of 1.55 lm by an interferometric technique. [3] DSTMS crystals are strongly anisotropic with refractive index of n a = 2.07 ± 0.05 along the polar a axis, and n b = 1.64 ± 0.05 along the b axis.…”

“…[10,11] DAST consists of a positively charged nonlinear optical chromophore stilbazolium and a negatively charged tosylate anion. The counter-ion tosylate is used in order to override the preferred antiparallel crystallization of the chromophores.…”

N-Methylquinolinium derivatives for photonic applications: Enhancement of electron-withdrawing character beyond that of the widely-used N-methylpyridinium

“…2a) were synthesized by a condensation of 4-(dimethylamino)benzaldehyde with the corresponding dimethylquinolinium 4-methylbenzenesulfonate (DMQ-T) intermediates in a similar manner as reported previously [33]. For comparison, the pyridinium-based DAST chromophore was synthesized by a condensation of 4-(dimethylamino)benzaldehyde with 1,4-dimethylpyridinium 4-methylbenzenesulfonate (DMP-T) in a similar manner as reported previously [27].…”