Xu Tian-Yi, Tong Fei, Xu Hui, Wang Meng-Qi, Tian He, Qu Da-Hui
Key Laboratory for Advanced Materials and Joint International Research Laboratory of Precision Chemistry and Molecular Engineering, Feringa Nobel Prize Scientist Joint Research Center, Frontiers Science Center for Materiobiology and Dynamic Chemistry, Institute of Fine Chemicals, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, The People's Republic of China.
J Am Chem Soc. 2022 Apr 13;144(14):6278-6290. doi: 10.1021/jacs.1c12485. Epub 2022 Mar 15.
Photomechanical molecular crystals are promising candidates for photoactuators and can potentially be implemented as smart materials in various fields. Here, we synthesized a new molecular crystal, ()-3-(naphthalen-1-yl)acrylaldehyde malononitrile (()-), that can undergo a solid-state [2 + 2] photocycloaddition reaction under visible light (≥400 nm) illumination. ()- microcrystals containing symmetric twinned sealed cavities were prepared using a surfactant-mediated crystal seeded growth method. When exposed to light, the hollow microcrystals exhibited robust photomechanical motions, including bending and dramatic directional expansion of up to 43.1% elongation of the original crystal length before fragmentation due to the photosalient effect. The sealed cavities inside the microcrystals could store different aqueous dye solutions for approximately one month and release the solutions instantly upon light irradiation. A unique slow-fast-slow crystal elongation kinematic process was observed, suggesting significant molecular rearrangements during the illumination period, leading to an average anisotropic crystal elongation of 37.0% (±3.8%). The significant molecular structure and geometry changes accompanying the photocycloaddition reaction, which propels photochemistry to nearly 100% completion, also facilitate photomechanical crystal expansion. Our results provide a possible way to rationally design molecular structures and engineer crystal morphologies to promote more interesting photomechanical behaviors.
光机械分子晶体是光致动器的有前途的候选材料，并有可能在各个领域作为智能材料得到应用。在此，我们合成了一种新的分子晶体，即（）-3-（萘-1-基）丙烯醛丙二腈（（）-），它在可见光（≥400 nm）照射下可发生固态[2 + 2]光环加成反应。使用表面活性剂介导的晶种生长方法制备了含有对称孪晶密封腔的（）-微晶。当暴露于光下时，空心微晶表现出强烈的光机械运动，包括弯曲以及由于光突出效应导致的高达原始晶体长度43.1%伸长的显著定向膨胀，直至破碎前。微晶内部的密封腔可以储存不同的水性染料溶液约一个月，并在光照时立即释放溶液。观察到独特的慢-快-慢晶体伸长运动过程，表明在光照期间发生了显著的分子重排，导致平均各向异性晶体伸长率为37.0%（±3.8%）。伴随光环加成反应的显著分子结构和几何形状变化推动光化学反应几乎完全完成，这也促进了光机械晶体膨胀。我们的结果为合理设计分子结构和工程化晶体形态以促进更有趣的光机械行为提供了一种可能的方法。
