Engineering of Organic Chromophores with Large Second-OrderOptical Nonlinearity and Superior Crystal Growth Ability.

We present two D-π-A organiccationic core structures leadingto 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 obtainedby the slow evaporation method. Two different polymorphic crystalsof both P–BI and S–BI were obtained from different polarsolvents. Kurtz powder tests revealed that the maximum second harmonicgeneration (SHG) efficiency of P–BI with monoclinic space group P21is 1.14 times the benchmark DAST(4-N,N-dimethylamino-4,-N,-methylstilbazolium tosylate). Bulk single crystals of P–BIwere obtained with size of up to 17.0 × 6.0 × 2.0 mm3without using seed crystals. This demonstrates that thismaterial exhibits great crystal growth ability along with a high second-orderoptical nonlinearity, making it a very attractive candidate for NLOapplications such as electro-optics and THz-wave generation. [ABSTRACT FROM AUTHOR]