Molecular dynamics study of crystalline molecular gyroscopes

In recent years molecular rotors have attracted the attention of many research groups for possible applications as new nanoscale devices and materials with controlled chemical, physical, and mechanical properties. One of the most unique systems with molecular rotations is amphidynamic molecular crystals, also known as crystalline molecular gyroscopes. This system can be viewed as a solid-state assembly of molecules that cannot move translationally but show internal rotations. Recent experiments on amphidynamic crystals indicate importance of rotational symmetry for describing their dynamics. However, mechanisms and rotational dynamic properties of molecular gyroscopes are still not well understood. We present here a theoretical investigation of amphidynamic crystals by utilizing extensive rigid-body molecular dynamics simulations and simple phenomenological arguments. Theoretical analysis suggests that intramolecular interactions within stator and rotator segments of molecular rotors as well as their flexibility strongly affect their crystal packing, energies and rotational behavior. Our quantitative predictions for dynamic properties agree well with available experimental results.