Engineering of Organic Chromophores with Large Second-Order Optical Nonlinearity and Superior Crystal Growth Ability

We present two D-π-A organic cationic core structures leading to highly efficient nonlinear optical (NLO) salts (E)-2-(4-(dimethylamino)­styryl)-1,1,3-trimethyl-1H-benzo­[e]­indol-3-ium iodide (P–BI) and (E)-2-(2-(5-(dimethylamino)­thiophen-2-yl) vinyl)-1,1,3 -trimethyl-1H-benzo­[e]­indol-3-ium iodide (S–BI). Single crystals of the above two materials were successfully obtained by the slow evaporation method. Two different polymorphic crystals of both P–BI and S–BI were obtained from different polar solvents. Kurtz powder tests revealed that the maximum second harmonic generation (SHG) efficiency of P–BI with monoclinic space group P21 is 1.14 times the benchmark DAST­(4-N,N-dimethylamino-4,-N,-methylstilbazolium tosylate). Bulk single crystals of P–BI were obtained with size of up to 17.0 × 6.0 × 2.0 mm3 without using seed crystals. This demonstrates that this material exhibits great crystal growth ability along with a high second-order optical nonlinearity, making it a very attractive candidate for NLO applications such as electro-optics and THz-wave generation.本研究报道了两种可制备高效非线性光学（nonlinear optical, NLO）盐的D-π-A型（Donor-π-Acceptor，给体-π-受体）有机阳离子核心骨架，具体为(E)-2-(4-(二甲氨基)苯乙烯基)-1,1,3-三甲基-1H-苯并[e]吲哚鎓碘盐（P–BI）与(E)-2-(2-(5-(二甲氨基)噻吩-2-基)乙烯基)-1,1,3-三甲基-1H-苯并[e]吲哚鎓碘盐（S–BI）。通过缓慢挥发法成功获得了上述两种材料的单晶；从不同极性溶剂中分别得到了P–BI与S–BI的两种不同多晶型晶体。库尔茨粉末测试结果显示，具有单斜空间群P2₁的P–BI的最大二次谐波产生（second harmonic generation, SHG）效率为基准材料DAST（4-N,N-二甲基氨基-4'-N'-甲基二苯乙烯唑鎓对甲苯磺酸盐）的1.14倍。无需使用晶种即可合成尺寸最大达17.0 × 6.0 × 2.0 mm³的块状P–BI单晶。这表明该材料兼具优异的晶体生长能力与较高的二阶光学非线性性能，是一类极具应用前景的NLO候选材料，可应用于电光器件、太赫兹波产生等NLO相关领域。