Ratchet-free solid-state inertial rotation of a guest ball in a tight tubular host

Dynamics of molecules in the solid state holds promise for connecting molecular behaviors with properties of bulk materials. Solid-state dynamics of [60]fullerene (C₆₀) is controlled by intimate intermolecular contacts and results in restricted motions of a ratchet phase at low temperatures. Manipulation of the solid-state dynamics of fullerene molecules is thus an interesting yet challenging problem. Here we show that a tubular host for C₆₀ liberates the solid-state dynamics of the guest from the motional restrictions. Although the intermolecular contacts between the host and C₆₀ were present to enable a tight association with a large energy gain of -14 kcal mol^-1, the dynamic rotations of C₆₀ were simultaneously enabled by a small energy barrier of +2 kcal mol^-1 for the reorientation. The solid-state rotational motions reached a non-Brownian, inertial regime with an extremely rapid rotational frequency of 213 GHz at 335 K.