[n]Pseudorotaxanes (n=2, 3) from Self-Assembly of Two Cryptands and a 1,2-Bis(4-pyridinium)ethane Derivative

Efficient hostguest complexation and interesting self-assembled structures formed between two crown ether-based cryptands and a 1,2-bis(4-pyridinium)ethane derivative 3 are reported. By self-assembly of cis-dibenzo-24-crown-8-based cryptand 1 and guest 3, a [3]pseudorotaxane was formed in solution, which further formed a supramolecular poly[3]pseudorotaxane structure in the solid state driven by pi-pi stacking interactions. Meanwhile, a [2]pseudorotaxane, obtained from self-assembly of a bis(m-phenylene)-32-crown-10-based cryptand 2 and guest 3, can form a supramolecular poly[2]pseudorotaxane structure in the solid state. This difference in the binding model reflects the diversity of hostguest chemistry of crown ether-based cryptands. Furthermore, these hostguest recognition processes and self-assembled structures were fully characterized by H-1 NMR, UV/Vis spectroscopy, electrospray ionization mass spectrometry, and single-crystal X-ray analysis. Interestingly, formation of the [3]pseudorotaxane between cryptand 1 and guest 3 can be reversibly controlled by adding and removing potassium cations in acetone. This reversible complexation process provides a simple on/off mechanism that can be used in the construction of controllable molecular switches.