A Photoswitchable Chloride‐Binding [2]Rotaxane

Control over the binding properties of anion receptors by external stimuli can be advantageous in various applications such as extraction and transport processes. Toward a light-responsive anion receptor with high binding affinity and selectivity, a stiff-stilbene photoswitch is incorporated into the macrocycle of a mechanically interlocked, chloride-binding [2]rotaxane structure. UV-Vis and ¹H NMR studies show reversible transformation between Z/E-isomers upon light irradiation, causing changes in motional dynamics and binding affinity. Photoswitching also takes place in the presence of chloride, as monitored by ¹H NMR spectroscopy, which results in its concomitant uptake and release. Our results show the suitability of rotaxanes as light-responsive ion receptors, which could serve as prototypes for supramolecular pumps.