Gyroscopes and the Chemical Literature, 2002-2020: Approaches to a Nascent Family of Molecular Devices.

Research directed toward the goal of molecular gyroscopes since the coverage of a previous review (2002) is described. Such species are a subclass of molecular rotors, which are comprised of rotators and stators. Major categories include (1) systems in which a rotator is embedded in a cage-like stator reminiscent of mechanical toy gyroscopes and (2) molecules that have been engineered to crystallize with parallel rotators and voids or other features that enable the rotator to rotate in the solid state (amphidynamic crystals). Particular attention is given to structural data and strategies for the minimization of rotational barriers. Synthetic routes are also described. Some allied types of molecules and supramolecular assemblies are also treated.