Azobenzene-Based Macrocyclic Arenes: Synthesis, Crystal Structures, and Light-Controlled Molecular Encapsulation and Release.

Azobenzene (azo)-based macrocycles are highly fascinating in supramolecular chemistry because of their light-responsiveness. In this work, a series of azo-based macrocyclic arenes 1, 2, 3, and 4, distinguished by the substituted positions of azo groups, is rationally designed and synthesized via a fragment-cyclization method. From the crystal and computed structures of 1, 2, and 3, we observe that the cavity size of these azo-macrocycles decreases gradually upon E→Z photoisomerization. Moreover, light-controlled host-guest complexations between azo-macrocycle 1 and guest molecules (7,7,8,8-tetracyanoquinodimethane, terephthalonitrile) are successfully achieved. This work provides a simple and effective method to prepare azo-macrocycles, and the light-responsive molecular-encapsulation systems in this work may further advance the design and applications of novel photo-responsive host-guest systems.