Photoinduced Mechanical Motions of Pseudorotaxane Crystals Composed of Azobenzene and Ferrocenyl Groups on an Axle and a Crown Ether Ring

This work describes the design and
characterization of photoresponsive dynamic pseudorotaxane crystals
composed of azobenzene and ferrocenyl groups in an ammonium cation
axle component threaded through dibenzo[24]­crown-8 ether rings. Pseudorotaxanes
provide flexibility for cis and trans isomerization of azobenzene
groups in a crystal state, enabling reversible bending motions under
alternating 360 and 445 nm laser irradiation. For such bending motions,
strained azobenzene structures were essential; these motifs were obtained
by increasing the bulkiness of the substituents on the axle and ring
molecules. In addition, the crystals showed photosalient effects,
such as jumping motions, under 445 nm laser irradiation. These motions
were assisted by the photoabsorption of the ferrocenyl group, which
converted 445 nm laser light into heat. The maximum lifting weight
accompanied by the photoinduced mechanical motion of a particular
crystal was estimated to be 9600 times the crystal weight. These pseudorotaxane
crystals exhibit promising features for applications in micro-nanometer-sized
miniature mechanical devices.

本项研究阐述了由叠氮苯和铁卡烯基团构成的氨离子轴组件穿过二苯并[24]冠-8醚环所形成的对光响应性动态假轮烷晶体的设计与表征。假轮烷晶体为叠氮苯基团在晶体状态下的顺反异构化提供了灵活性，使其能够在交替的360 nm和445 nm激光照射下实现可逆的弯曲运动。此类弯曲运动依赖于应变叠氮苯结构的必要性；通过增大轴和环分子上取代基的体积，获得了这些结构模式。此外，晶体在445 nm激光照射下展现出显著的光电效应，如跳跃运动，这些运动得益于铁卡烯基团的光吸收，将445 nm激光光能转化为热能。特定晶体的光诱导机械运动所伴随的最大提升重量估计为晶体重量的9600倍。这些假轮烷晶体在微型纳米级微型机械装置的应用中展现出巨大的潜力。