Wang Zhihua, Han Wenqing, Fu Bona, Kang Hanwen, Cheng Puxin, Guan Junjie, Zheng Yongshen, Shi Rongchao, Xu Jialiang, Bu Xian-He
School of Materials Science and Engineering, Tianjin Key Laboratory of Metal and Molecular Materials Chemistry, Frontiers Science Center for New Organic Matter, Nankai University, Tongyan Road 38, Tianjin 300350, P. R. China.
SINOPEC (Beijing) Research Institute of Chemical Industry Co., Ltd. Yanshan Branch, Fenghuangting Road 15, Beijing 102500, P. R. China.
J Am Chem Soc. 2025 Jan 22;147(3):2766-2775. doi: 10.1021/jacs.4c15519. Epub 2025 Jan 7.
Flexible molecular crystals are essential for advancing smart materials, providing unique functionality and adaptability for applications in next-generation electronics, pharmaceuticals, and energy storage. However, the optical applications of flexible molecular crystals have been largely restricted to linear optics, with nonlinear optical (NLO) properties rarely explored. Herein, we report on the application of mechanical twisting of flexible molecular crystals for second-order nonlinear optics. The crystal formed through the self-assembly of the model compound 9-anthraldehyde () features an intrinsic chiral and noncentrosymmetric structure, demonstrating high efficiency second harmonic generation (SHG) and NLO circular dichroism, which could be greatly enhanced by macroscopic mechanical twisting. The anisotropic molecular stacking imparts the crystal with mechanical flexibility of combined elastic bending and plastic twisting. The isochiral mechanical twisting could greatly enhance the SHG intensities by an order of magnitude depending on their - or -configuration. Meanwhile, the SHG circular dichroism factor of the isochiral twisted crystal is greatly increased, achieving the highest reported NLO anisotropy factor among organic NLO materials. These boosted NLO performances of SHG intensity and nonlinear chiroptical response are expected to greatly expand the photonic applications of flexible molecular crystals.
柔性分子晶体对于推动智能材料的发展至关重要，为下一代电子学、制药和能量存储应用提供独特的功能和适应性。然而，柔性分子晶体的光学应用在很大程度上局限于线性光学，非线性光学（NLO）特性很少被探索。在此，我们报道了柔性分子晶体的机械扭转在二阶非线性光学中的应用。通过模型化合物9-蒽醛（）自组装形成的晶体具有固有的手性和非中心对称结构，表现出高效的二次谐波产生（SHG）和NLO圆二色性，通过宏观机械扭转可以大大增强。各向异性的分子堆积赋予晶体兼具弹性弯曲和塑性扭转的机械柔韧性。等手性机械扭转可根据其 - 或 - 构型将SHG强度极大地增强一个数量级。同时，等手性扭曲晶体的SHG圆二色性因子大幅增加，在有机NLO材料中实现了报道的最高NLO各向异性因子。SHG强度和非线性手性光学响应的这些增强的NLO性能有望极大地扩展柔性分子晶体的光子应用。
