Evaluation of Hydrogen-Bond Acceptors for Redox-Switchable Resorcin[4]arene Cavitands

Various H-bond acceptor groups were
evaluated for their propensity
to induce conformational switching between the kite and vase forms
of diquinone-diquinoxaline resorcin[4]­arene cavitands upon redox interconversion.
The H-bond acceptors were placed on the quinoxaline walls with the
purpose of stabilizing the vase form only in the reduced hydroquinone
state of the cavitand by forming H-bonds with the hydroquinone OH
groups. Design guidelines for successful acceptors were derived. The
carboxamide acceptor was shown to be the best candidate. Based on
this moiety, a redox-switchable triptycene-based basket that can completely
sterically encapsulate a guest in its closed vase conformation was
prepared. The basket binds small molecule guests with association
constants of up to 104 M–1 in mesitylene-d12 and exhibits slow guest exchange kinetics
with a half-life for guest release in the order of 104 s.