The design and synthesis of three organic nonlinear optical crystals is presented for terahertz (THz) generation that incorporates the optimal characteristics of known organic nonlinear optical crystals 4-(4-(dimethylamino)styryl)-1-methylpyridinium 4- methylbenzenesulfonate (DAST) and 2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate (HMQ-TMS). The three crystals feature the 4-((4-(dimethylamino)phenyl)ethynyl)-1-methylpyridin-1-ium (4DEP) cation and three different anion combinations. Gas phase ab initio calculations of the cation show that 4DEP has a larger hyperpolarizability than cations from both DAST and HMQ-TMS. To obtain the molecular packing needed for large nonlinear optical susceptibility and efficient THz generation, three anions are tested that result in noncentrosymmetric crystals: 4- methylbenzenesulfonate, 3-nitrobenzenesulfonate, and napthalene-2-sulfonate. After synthesis and crystallization, the crystal structure is characterized via X- ray diffraction (XRD) analysis, and the relative THz generation efficiency for ideal crystals is predicted. 4DEP-N2S shows a roughly 30 larger relative second-order nonlinear optical susceptibility compared to HMQ-TMS and DAST and, therefore, shows promise as a new advanced THz generation crystal.
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