Adjusting the photomechanical behavior and mechanical properties of photoactive crystals is a challenging goal, especially for the same photoactive molecule. In this study, cocrystals of 4-aminoazobenzene (AAB) with a series of coformers containing pyridyl groups were designed to tune its photobending behavior and elasticity. 5 AAB-based cocrystals exhibiting different photomechanical behaviors and elasticity were obtained. The structure-related bending behaviors of these cocrystals were correlated to the dihedral angles between AAB molecules and the bending faces. A rarely observed photoinduced curling was discovered on the AAB–4,4′-bipyridine (BIP) cocrystal according to this structure–property correlation. Excellent elasticity was achieved on the AAB–4-(1-naphthylvinyl)pyridine (NPE) cocrystal. The molecular mechanism analysis revealed that the formation of large dispersive weak interactions and molecular interlocking are essential to improving the elasticity. Typical irreversible plastic deformation was found on the AAB–BIP cocrystal which was attributed to the appearance of slip planes connected via weak interactions. This demonstrated that the photomechanical properties and elasticity are closely related to the supramolecular packing and can be tuned via cocrystallization. Cocrystallization and the results of this work could be useful to expand the variety of photomechanical molecular crystals, and tune the photobending behavior and improve the elasticity of molecular crystals.

中文翻译：

---

通过共晶工程调节偶氮苯的光机械性能和优异的弹性

调整光活性晶体的光机械行为和机械性能是一个挑战性的目标，尤其是对于相同的光活性分子而言。在这项研究中，设计了4-氨基偶氮苯（AAB）与一系列含有吡啶基的共形成物的共晶体，以调节其光弯曲行为和弹性。获得了5种显示出不同光机械行为和弹性的AAB基共晶体。这些共晶体的结构相关的弯曲行为与AAB分子和弯曲面之间的二面角相关。根据这种结构与性质的相关性，在AAB-4,4'-联吡啶（BIP）共晶体上发现了很少见的光致卷曲。在AAB-4-（1-萘乙烯基）吡啶（NPE）共晶体上获得了出色的弹性。分子机理分析表明，大分散弱相互作用的形成和分子互锁对提高弹性至关重要。在AAB–BIP共晶体上发现了典型的不可逆塑性变形，这归因于连接的滑移面的出现通过弱互动。这表明光机械性质和弹性与超分子堆积紧密相关，并且可以通过共结晶来调节。共结晶和这项工作的结果可能有助于扩大光机械分子晶体的种类，调节光弯曲行为并改善分子晶体的弹性。