Wang Chi-Hsien, Lin Yi-Chia, Bhunia Surojit, Feng Yuanning, Kundu Pramita, Stern Charlotte L, Chen Pei-Lin, Stoddart J Fraser, Horie Masaki
Department of Chemical Engineering, National Tsing Hua University, 101, Sec. 2, Kuang-Fu Road, Hsinchu 30013, Taiwan.
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
J Am Chem Soc. 2023 Oct 4;145(39):21378-21386. doi: 10.1021/jacs.3c06371. Epub 2023 Sep 21.
Stimuli-responsive molecular crystals have attracted considerable attention as promising smart materials with applications in various fields such as sensing, actuation, and optoelectronics. Understanding the structure-mechanical property relationships, however, remains largely unexplored when it comes to functionalizing these organic crystals. Here, we report three polymorphic crystals (, , and ) formed by the non-threaded complexation of a dibenzo[18]crown-6 (DB18C6) ether ring and an azobenzene-based ammonium cation, each exhibiting distinct thermal phase transitions, photoinduced deformations, and mechanical behavior. Structural changes on going from to and from to during heating and cooling, respectively, are observed by single-crystal X-ray crystallography. shows photoinduced reversible bending, whereas exhibits isotropic expansion. displays uniaxial negative expansion with a remarkable increase of 44% in thickness under photoirradiation. Force measurements and nanoindentation reveal that the soft crystals of with a low elastic modulus demonstrate a significant photoresponse, attributed to the non-threaded molecular structure, which permits flexibility of the azobenzene unit. This work represents a significant advance in the understanding of the correlation between structure-thermomechanical and structure-photomechanical properties necessary for the development of multi-stimulus-responsive materials with tailored properties.
刺激响应性分子晶体作为一种有前景的智能材料，在传感、驱动和光电子学等各个领域具有应用潜力，因而备受关注。然而，在对这些有机晶体进行功能化时，结构与力学性能之间的关系在很大程度上仍未得到探索。在此，我们报道了由二苯并[18]冠-6（DB18C6）醚环与基于偶氮苯的铵阳离子通过非穿线络合形成的三种多晶型晶体（α、β和γ），每种晶体都表现出独特的热相变、光致变形和力学行为。通过单晶X射线晶体学分别观察到在加热和冷却过程中从α到β以及从β到γ的结构变化。α表现出光致可逆弯曲，而β表现出各向同性膨胀。γ在光照射下呈现单轴负膨胀，厚度显著增加44%。力测量和纳米压痕表明，具有低弹性模量的γ软晶体表现出显著的光响应，这归因于非穿线分子结构，该结构允许偶氮苯单元具有灵活性。这项工作代表了在理解结构 - 热机械和结构 - 光机械性能之间的相关性方面取得的重大进展，这对于开发具有定制性能的多刺激响应材料是必要的。
