Order-disorder transition of dipolar rotor in a crystalline molecular gyrotop and its optical change.

Successful control of the orientation of the π-electron systems in media has been achieved in certain liquid crystals, making them applicable to devices for optical systems because of the variation in the optical properties with the orientation of the π-electron system. However, because of close packing, changing the orientation of molecules in the crystalline state is usually difficult. A macrocage molecule with a bridged thiophene rotor was synthesized as a molecular gyrotop having a dipolar rotor, given that the dipole derived from the thiophene can rotate even in the crystal. The thermally induced change in the orientation of the dipolar rotors (thiophene ring) inside the crystal, i.e., order-disorder transition, and the variation in the optical properties in the crystalline state were observed.