Chiral Plastic Crystal of Solid-State Dual Rotators

A dual molecular rotor N-adamantyl camphor sulfonamide (ADCS) consisting of adamantane (AD) and camphor (CA) linked by a sulfonamide (−SO2NH−) bond was designed to form a chiral plastic crystal. Chiral 1S-ADCS and racemic rac-ADCS crystals exhibited a phase transition from the crystal to the plastic crystal phase upon heating at approximately 400 K, as confirmed by optical, structural, and dielectric measurements. In the plastic crystal phase, both the AD and CA units have thermally activated motional freedom and their dynamics freeze to form a low-temperature plastic crystal phase rather than a crystal phase. The most stable and metastable ADCS conformations coexist in the as-grown crystalline phase, and the dynamic behavior of the plastic crystal phase makes it difficult to recover the initial conformations necessary for the formation of the closest packing structure upon cooling, resulting in a phase transition to the plastic crystalline state. The as-grown white crystals of both 1S-ADCS and rac-ADCS exhibited weak luminescence, whereas the phase transition from glass to transparent plastic crystals changed to a non-fluorescent state.