A Molecular Balloon: Expansion of a Molecular Gyrotop Cage Due to Rotation of the Phenylene Rotor

A macrocage molecule with a bridged phenylene rotor has
been reported
as a molecular gyrotop, because the rotor can rotate even in a crystalline
state. Although the most stable cage structure of the molecular gyrotop
in a crystal was folded and shrunken at low temperature, expansion
of the cage was observed at high temperature due to rapid rotation
of the phenylene in a crystal. This phenomenon is analogous to the
deflation and inflation of a balloon. Moreover, the unusually large
thermal expansion coefficient of the crystal was estimated in the
temperature range in which the expansion of the cage was observed,
indicating a new function of dynamic states of the molecules.