Photoinduced multi-directional deformation of azobenzene molecular crystals
Photoinduced multi-directional deformation of azobenzene molecular crystals
复制标题
偶氮苯分子晶体的光致多向变形
DOI：
10.1039/c8tc04631j
复制
发表时间：
2019-01-21
影响因子：
6.4
通讯作者：
Yu, Haifeng
中科院分区：
文献类型：
--
作者：
Hao, Yunhui;Huang, Shuai;Yu, Haifeng
开发仿生刺激响应材料来模拟动植物的运动一直是材料科学和工程学中一个非常令人兴奋的研究领域。然而，用单组分材料实现多种形式的运动仍然是极具挑战性的。本文首次用4-氰基-4‘-戊氧基偶氮苯(AZ)片状晶体实现了光致多向变形。在紫外光照射下，在不同的温度范围内观察到三种不同类型的光机械运动：第一，当温度保持在顺-AZ(MPCA)的熔点以下时，实现了快速且可逆地偏离光源的光机械弯曲。其次，当温度高于MPCA的熔点时，观察到向光源的光致弯曲。第三，在MPCA熔点以下和熔点附近的温度范围内，由于光异构化引起的体积膨胀和光热效应辅助下的相变引起的体积收缩之间的竞争，实现了全双向运动。通过温度调节，同一晶体样品在相同的光照条件下的光定向多向运动，标志着一类新的、多功能的光可控单组分分子晶体，并通过光异构化和光热效应的结合，为光机械致动器的操作提供了一个新的控制水平。
Developing biomimetic stimuli-responsive materials to imitate movements found in plants and animals has been a very exciting research field in materials science and engineering. However, achieving multiple forms of motion with a mono-component material is still extremely challenging. Here, photoinduced multi-directional deformations were firstly achieved with plate-like crystals of 4-cyano-4'-pentyloxy azobenzene (AZ). Upon irradiation of UV light, three separate types of photomechanical motions are observed in different temperature regimes: Firstly, a rapid and reversible photomechanical bending away from the light source was achieved when the temperature was kept below the melting point of cis-AZ (MPCA). Secondly, photoinduced bending towards the light source was observed when the temperature was higher than the melting point of MPCA. Thirdly, fully bidirectional motions were achieved in the temperature regime below but near the melting point of MPCA, due to a competition between photoisomerization-induced volume expansion and phase-transition caused volume contraction, aided by a photothermal effect. The light-directed multi-directional motions of the same crystal sample under the same photoirradiation conditions enabled by temperature tuning demonstrated here signify a new and versatile class of photocontrollable mono-component molecular crystals and provide a novel level of control of operation for photomechanical actuators by combination of photoisomerization and photothermal effects.