A Crystalline Supramolecular Switch: Controlling the Optical Anisotropy through the Collective Dynamic Motion of Molecules

Going 'round the twist: Single crystals of a ferrocenyl-substituted pseudorotaxane have different structures at 30 and 128 °C owing to a thermal crystalline phase transition. This change in crystal structure results from a conformational change that involves rotation of the aromatic ring of the axle component (see scheme), and cooperative unidirectional rotation of the molecules alters the optical anisotropy of the crystal.