Upgrading Pillar[n]arenes to Reversible Photocontrolled Self-Folding Hosts for Photoswitchable Guest Uptake/Release and Self-Assembly

Abstract

Photoresponsive macrocycles can serve as versatile supramolecular platforms for exploring remote-controllable self-assembly systems and materials. However, reconciling excellent host-guest properties with robust photocontrollable capabilities persists as a formidable yet pivotal challenge in the design and construction of photoresponsive macrocycles. Herein, we demonstrate a photocontrolled self-folding strategy to obtain a new class of photoswitchable macrocycles, AzoP[5/6]A, by directly introducing an azobenzene (azo) unit onto the pillararene macrocycle scaffolds, which does not degrade guest-binding ability and yet allow for significant ON/OFF photoswitching. It transpires that when the azo unit adopts the E-configuration, these AzoP[5/6]A feature a guest-accessible cavity and exhibit comparable guest-binding ability to that of the pristine alkylated pillararenes. However, as the azo unit undergoes photoisomerization from E to Z, these AzoP[5/6]A fold into the blocked cavities self-filled with partial Z-azo module, causes the dramatic reduction of binding affinity towards guest molecules by up to 1×10⁴-fold, resulting in efficient release of guests from macrocycle cavity. Furthermore, in the presence or absence of guests, these azopillararenes could all show high bidirectional E⇆Z photoconversion (up to ≥ 95%). These unique properties further benefit the fabrication of host-guest supramolecular polymeric network featuring photoswitchable self-assembly behavior. .