Structure and Dynamics of Crystalline Molecular Gyrotops with a Difluorophenylene Rotor

Macrocage molecules with a bridged π-electron system could be assumed as crystalline molecular gyrotops because of the structural similarity and the rotatable π-electron system. In this study, 1,2-difluoro-3,6-phenylene-bridged macrocages were designed and synthesized as crystalline molecular gyrotops with a dipolar rotor. The thermal ring dynamics of the dipolar rotor in the crystal were investigated by solid-state NMR and dielectric spectroscopy. The gyrotop that was surrounded by three C14-alkyl chains exhibited an exchange between two stationary positions in the crystalline state. In contrast, the gyrotop cage consisting of C18 chains exhibited no dynamics in the crystalline state. Although the corresponding phenylene derivatives exhibit a facile rotational motion of the phenylene group in the crystalline state, the dynamics of each derivative was observed to be different. The reason for this difference is ascribed to the difference in the bulkiness between the fluorine and hydrogen atoms in the rotor.