Multi-State Redox and Light-Driven Switching of Pseudorotaxanation and Cation Shuttling.

The modulation of molecular recognition underpins numerous wide-ranging applications and has inspired the development of a myriad of switchable receptors, in particular photo- or redox-responsive hosts. Herein, we report a highly versatile three-state cation receptor family and switch system based on an overcrowded alkene strapped with crown ethers, which can be switched by both redox and light stimuli, thereby combining the advantages of both approaches. Specifically, the neutral switches can be quantitatively converted between and folded receptor geometries by irradiation, leading to the discovery of a significant increase or decrease in cation binding affinity, which was exploited to shuttle the pseudorotaxane-forming dibenzylammonium guest between the switchable crown ethers of slightly different sizes. Alternatively, two-electron oxidation to the orthogonal, dicationic, nonvolatile state completely turns off cation binding to the host, thereby ejecting the guest. Upon reduction, the metastable folded state is first formed, which then thermally relaxes, resulting in a unique, autonomous, and cation-dependent multistate switching cascade.