Stimulus-responsive molecular rotors: Control of rotary motion in triptycene–ionophore systems with s-block metal cations

Triptycene derivatives bearing a pair of ionophores were synthesized and their rotational behaviors were observed with/without s-block metal cations as an external stimulus. In this study, oxyethylene-based ionophores were introduced at both bridgehead positions of triptycene as the stimulus receptors. The NMR experiments revealed the formation of complexes of the triptycenes with the s-block metal cations. We demonstrated that the rate (activation energy) of the internal rotation of the triptycyl moiety could be controlled by the formation of the complexes. We also found that the conformation of those complexes can be controllable with the species of metal cations.