A Dynamic Hydrogen‐Bonded Azo‐Macrocycle for Precisely Photo‐Controlled Molecular Encapsulation and Release

Abstract

A light‐responsive system constructed from hydrogen‐bonded azo‐macrocycles demonstrates precisely controlled propensity in molecular encapsulation and release process. A significant decrease in the size of the cavity is observed in the course of the E→Z photoisomerization based on the results from DFT calculations and traveling wave ion mobility mass spectrometry. These macrocyclic hosts exhibit a rare 2:1 host–guest stoichiometry and guest‐dependent slow or fast exchange on the NMR timescale. With the slow host–guest exchange and switchable shape change of the cavity, quantitative release and capture of bipyridinium guests is achieved with the maximum release of 68 %. This work underscores the importance of slow host–guest exchange on realizing accurate release of organic cations in a stepwise manner under light irradiation. The light‐responsive system established here could advance further design of novel photoresponsive molecular switches and mechanically interlocked molecules.

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

“…Azobenzene (Azo), owing a light‐induced E ↔ Z isomerized feature, is an outstanding building block for light responsive structures and materials [24–27] . To date, just few examples of macrocycles containing azo units were reported [28–31] . However, these photo‐responsive macrocycles usually need relatively complicated organic synthesis and purification, which greatly impeded the development of photo‐responsive macrocycles.…”

“…[24][25][26][27] To date, just few examples of macrocycles containing azo units were reported. [28][29][30][31] However, these photo-responsive macrocycles usually need relatively complicated organic synthesis and purification, which greatly impeded the development of photo-responsive macrocycles. In addition, these azo-macrocycles were constructed by para-substituted azos, macrocycles fabricated by meta-and ortho-substituted azos have been rarely reported.…”

Recent Advances of Photoresponsive Supramolecular Switches

“…b) The amount of the precisely released guest as a function of irradiation time. Reproduced with permission [26] . Copyright 2019, Wiley‐VCH.…”

“…In addition to the hosts mentioned above, some novel photoresponsive macrocycles [22][23][24][25][26] have also been reported. These photoresponsive macrocyclic compounds are built with incorporated photoactive azo moieties in their molecular backbones.…”

“…Reproduced with permission. [26] Copyright 2019, Wiley-VCH. engulf guests because of the lack of inward-pointing functional groups as binding sites.…”