Anion-Regulated Molecular Rotor Crystal: The First Case of a Stator–Rotator Double Switch with Relaxation Behavior

Molecular
rotational motion is crucial in artificial molecular
machines and is expected to be very significant for the development
of an electronic information molecular machine as mentioned in the
2016 Nobel Prize. However, controlling multiple motor modes is a huge
challenge. Here, we report a case in which the structural phase transition
effectively triggers multiple motor modes by regulating the rotational
speed of the cation and/or anion. A novel switchable crystalline supramolecular
rotor, [(cyclohexylammonium)­(18-crown-6)] FSO3 (1), exhibits prominent temperature-dependent double switching behavior
at 157.9 and 389.1 K induced by the variation of the rotational speed
of the FSO3– anion (which acts as a super
miniature rotator) in response to temperature. Moreover, it exhibits
significant relaxation behavior and excellent pyroelectric switch
characteristics. To the best of our knowledge, this might be the first
discovery of the stator–rotator double switch with a relaxation
effect, which could be a promising candidate for a slow/fast responsive
double switch over a wide temperature range.