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 macrocycle, AzoP[5/6]A, by directly introducing an azobenzene (azo) unit onto the pillararene macrocycle scaffold, which does not impair the guest binding ability yet allows 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 configurations with blocked cavities self-filled with partial Z-azo modules, which causes a dramatic reduction of the binding affinity towards the guest molecules by up to 1 × 10⁴-fold, resulting in efficient release of guests from the 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 networks featuring photoswitchable self-assembly behavior.