Hasebe Shodai, Hagiwara Yuki, Asahi Toru, Koshima Hideko
Graduate School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo, 169-8555, Japan.
Present address: Institute for Molecular Systems Engineering and Advanced Materials (IMSEAM), Heidelberg University, Im neuenheimer Feld 225, Heidelberg, 69120, Germany.
Angew Chem Int Ed Engl. 2025 Jan 2;64(1):e202418570. doi: 10.1002/anie.202418570. Epub 2024 Nov 11.
Photomechanical crystals exhibit mechanical motion upon light irradiation and may thus find applications as actuators. Over the last decades, many photomechanical organic crystals have been developed, commonly via photochemical reactions, particularly photoisomerization. However, photochemical crystal actuation is associated with several drawbacks, including a limited number of available crystals, slow actuation speed (<5 Hz), and narrow wavelength range (<550 nm). Such constraints have hindered the widespread use of crystals as actuation materials. In this minireview, we focus on crystal actuation by employing more universal physical phenomena (the photothermal effect and photothermally resonated natural vibration) and quantitatively evaluate actuation performance. Both mechanisms, particularly the latter, outperformed conventional photomechanical crystal activation in terms of both speed (maximum: 1,350 Hz) and the useful wavelength range (ultraviolet to near-infrared). The oscillation frequencies of the crystals exceeded those of polymers, efficiently filling the gap between soft and hard materials. Both the photothermal effect and natural vibration can actuate any crystal that absorbs light. These two versatile physical actuation mechanisms could expand 40 years of research on photomechanical crystals-which had been based on photochemical reactions-from the realm of chemistry into engineering and lead to their practical applications in actuators and soft robots.
光机械晶体在光照下会产生机械运动，因此有望用作致动器。在过去几十年中，人们开发了许多光机械有机晶体，通常是通过光化学反应，特别是光异构化反应。然而，光化学晶体致动存在几个缺点，包括可用晶体数量有限、致动速度慢（<5 Hz）以及波长范围窄（<550 nm）。这些限制阻碍了晶体作为致动材料的广泛应用。在这篇综述中，我们专注于利用更普遍的物理现象（光热效应和光热共振自然振动）来实现晶体致动，并定量评估致动性能。这两种机制，尤其是后者，在速度（最高可达1350 Hz）和有用波长范围（紫外到近红外）方面都优于传统的光机械晶体激活方式。晶体的振荡频率超过了聚合物，有效地填补了软材料和硬材料之间的空白。光热效应和自然振动都可以驱动任何吸收光的晶体。这两种通用的物理致动机制可以将基于光化学反应的光机械晶体40年的研究从化学领域扩展到工程领域，并使其在致动器和软机器人中得到实际应用。
