“…However, certain intermolecular arrangements of the rotors in a crystal can allow correlated motion between multiple neighboring rotators, which effectively creates a molecular gear (Figure c). Recently, the design of crystals formed of molecules that demonstrate correlated mechanical motion has attracted significant interest in the field of crystalline molecular machines. − In particular, gear-like molecular rotation via multiple neighboring rotary moieties has been noted as an attractive target given the ability to transmit mechanical force at the molecular level and because the alternation of molecular geometry can be related to the physical properties of solids. − Correlated motion implies a reduction in entropy due to a decrease in the number of allowed geometries during the dynamic processes, resulting in a negative value in the entropy change (Δ S ‡ ) for the rotational frequency (Figure c) …”