A Photoswitchable Macrocycle Controls Anion-Templated Pseudorotaxane Formation and Axle Relocalization

Important biological processes, such as signaling and transport, are regulated by dynamic binding events. The development of artificial supramolecular systems in which binding between different components is controlled could help emulate such processes. Herein, we describe stiff-stilbene-containing macrocycles that can be switched between (Z)- and (E)-isomers by light, as demonstrated by UV/Vis and 1H NMR spectroscopy. The (Z)-isomers can be effectively threaded by pyridinium halide axles to give pseudorotaxane complexes, as confirmed by 1H NMR titration studies and single-crystal X-ray crystallography. The overall stability of these complexes can be tuned by varying the templating counteranion. However, upon light-induced isomerization to the (E)-isomer, the threading capability is drastically reduced. The axle component, in addition, can form a heterodimeric complex with a secondary isophthalamide host. Therefore, when all components are combined, light irradiation triggers axle exchange between the macrocycle and this secondary host, which has been monitored by 1H NMR spectroscopy and simulated computationally. Anion-templated pseudorotaxane formation is effectively controlled by macrocycles that expand and contract in response to a light stimulus. Upon light-induced threading and dethreading, the axle component can dynamically relocate between the macrocycle and a secondary isophthalamide host. This work is a stepping stone towards signal processing in multicomponent supramolecular systems.image