Pretransitional Layer Contraction at the Chiral Smectic A-to-Chiral Smectic C Phase Transition of a Chiral Nitroxide Radical

We have designed and synthesized a new chiral paramagnetic liquid crystalline compound with a nitroxide radical moiety showing chiral smectic A (SmA*) and C (SmC*) phases. This compound shows pretransitional layer contraction prior to the SmA*-to-SmC* phase transition in the cooling run. Electron paramagnetic resonance spectroscopy, X-ray diffraction analysis, and polarized optical microscopy reveal that a temperature-dependent conformational change is responsible for the pretransitional layer contraction.