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 anti- and syn-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 syn-folded state is first formed, which then thermally relaxes,
resulting in a unique, autonomous, and cation-dependent multistate
switching cascade.