Methyl Made Noncentrosymmetric Stacking: A Promising Organic Single Crystal for Highly Efficient Terahertz-wave Generation
Regulating secondary bonds in organic compounds is one of the important routes to design practical materials with excellent performances. However, it is still a great challenge to control molecular arrangement and spatial configuration by changing limited substituent groups. Herein, two indolium-based (C19H20NO)+ crystals, centric OHI-CBS and acentric OHI-T were synthesized and grown by evaporation method. An intriguing structural change from centrosymmetric (P21/c) to noncentrosymmetric (Cc) space group was obtained by a simple substitution from chloro- to methyl. Theoretical calculations demonstrate hydrogen bonds and π-π interactions make a dominated contribution to molecular spatial alignment. Meanwhile, OHI-T crystal exhibits prominent nonlinearity about 0.7 times that of the benchmark OH1 crystal, wide band gap (2.47 eV), wide transparency range (504 - 2100 nm), and remarkably efficient output energy among 0.1 - 20 THz region, suggesting it is a potential nonlinear optical media for THz-wave generation. This work realizes the rational crystal structural regulation by simple molecular subsitution and provides a feasible design strategy for other organic optoelectronic functional materials.