Imato Keiichi, Ishii Akira, Kaneda Naoki, Hidaka Taichi, Sasaki Ayane, Imae Ichiro, Ooyama Yousuke
Applied Chemistry Program, Graduate School of Advanced Science and Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashihiroshima 739-8527, Japan.
JACS Au. 2023 Aug 21;3(9):2458-2466. doi: 10.1021/jacsau.3c00213. eCollection 2023 Sep 25.
Molecular photoswitches are extensively used as molecular machines because of the small structures, simple motions, and advantages of light including high spatiotemporal resolution. Applications of photoswitches depend on the mechanical responses, in other words, whether they can generate motions against mechanical forces as actuators or can be activated and controlled by mechanical forces as mechanophores. Sterically hindered stiff stilbene (HSS) is a promising photoswitch offering large hinge-like motions in the / isomerization, high thermal stability of the isomer, which is relatively unstable compared to the isomer, with a half-life of ca. 1000 years at room temperature, and near-quantitative two-way photoisomerization. However, its mechanical response is entirely unexplored. Here, we elucidate the mechanochemical reactivity of HSS by incorporating one or isomer into the center of polymer chains, ultrasonicating the polymer solutions, and stretching the polymer films to apply elongational forces to the embedded HSS. The present study demonstrated that HSS mechanically isomerizes only in the to direction and reversibly isomerizes in combination with UV light, i.e., works as a photomechanical hinge. The photomechanically inducible but thermally irreversible hinge-like motions render HSS unique and promise unconventional applications differently from existing photoswitches, mechanophores, and hinges.
分子光开关因其结构小、运动简单以及光具有高时空分辨率等优点而被广泛用作分子机器。光开关的应用取决于其机械响应，换句话说，取决于它们能否作为致动器产生抵抗机械力的运动，或者能否作为机械传感分子被机械力激活和控制。空间位阻刚性二苯乙烯（HSS）是一种很有前景的光开关，在顺反异构化过程中呈现出类似铰链的大幅度运动，反式异构体具有高热稳定性，而顺式异构体相对不稳定，在室温下半衰期约为1000年，并且具有近乎定量的双向光异构化。然而，其机械响应尚未得到充分研究。在此，我们通过将一个反式或顺式异构体引入聚合物链中心、超声处理聚合物溶液以及拉伸聚合物薄膜以对嵌入的HSS施加拉伸力，来阐明HSS的机械化学反应性。本研究表明，HSS仅在反式到顺式方向发生机械异构化，并与紫外光结合发生可逆异构化，即起到光机械铰链的作用。这种光机械诱导但热不可逆的类似铰链的运动使HSS独具特色，并有望实现与现有光开关、机械传感分子和铰链不同的非常规应用。
