Solid-State 2H NMR Study for Deuterated Phenylene Dynamics in a Crystalline Gyroscope-Like Molecule

Abstract

Molecular rotors have earned substantial popularity in recent times, owing to the unique dependence of its crystalline properties on the rotational dynamics of the rotor. We have recently reported the synthesis and crystal structure of a phenylene-bridged macrocage as a gyroscope-like molecule in the crystalline state. The dynamics of the phenylene moiety was probed by solid-state 13C CP/MAS proton dipolar dephasing NMR spectroscopy. Herein, solid-state 2H NMR studies were performed to study the dynamics of the gyroscope-like molecule with a deuterated rotor in the crystalline state. A spectrum with a narrow line shape was obtained at 300 K. The facile exchange among three stationary states, which was observed by X-ray crystallography, was clearly confirmed. Additionally, a crystal-to-crystal phase transition that switches the motion of the rotor was observed in the DSC analysis of the powdered sample.