Complexation between pentiptycene derived bis(crown ether)s and CBPQT4+ salt: ion-controlled switchable processes and changeable role of the CBPQT4+ in host-guest systems

The pentiptycene derived bis(crown ether)s with two 24-crown-8 moieties in the cis position could include the CBPQT(4+) ring inside their cavities to form 1:1 complexes, and the naphthalene groups connected in the crown ether moieties showed less effective complexation ability toward the CBPQT(4+) ring than the host containing two terminal benzene rings. This result was probably due to the stereohindrance effect of the naphthalene groups, and it was obviously different from that of the pentiptycene derived mono(crown ether)s. For the pentiptycene derived bis(crown ether) with two 24-crown-8 moieties in the trans position, it formed a 1:2 stable complex with the CBPQT(4+) salt in solution and in the solid state, in which the pentiptycene moiety played an important role in stabilizing the complex. Moreover, binding and release of the CBPQT(4+) ring in the complexes based on the pentiptycene-derived crown ethers could be chemically controlled by adding and removing potassium ions, in which the complexation modes played the key role. Interestingly, it was further found that switching the role of the CBPQT(4+) ring in host and guest systems based on the pentiptycene derived bis(crown ether)s was easily achieved, which represents a new kind of supramolecular system.