Interlayer Interactions Induced by Amphiphilicities of a Rod-Like Molecule Produce Frustrated Structures in Conventional Calamitic Phases

We prepared a rod-like molecule, 4-[4-(7-hydroxyheptyloxy)phenyl]-1-(4-hexylphenyl)-2,3-difluorobenzene, and investigated its physical properties using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The compound was found to exhibit nematic, smectic A, and smectic C phases. A smectic-like layer ordering was detected using XRD at low temperatures of the nematic phase. The nematic phase changed to a smectic A phase when cooled, with no accompanying enthalpy change. Analyses using XRD and POM revealed that the smectic C phase consists of three states: conventional SmC with a monolayered structure, monolayered SmC' possessing an additional weak bilayered character, and SmC '' possessing both monolayered and bilayered structures. Furthermore, a discontinuous increase in birefringence of a homeotropically aligned sample of the compound was observed in the SmC '' phase. Interlayer interactions organized by hydrophobic-hydrophilic amphiphilicity and orthogonal-tilt amphiphilicity are discussed to explain the appearance of the unusual liquid-crystalline phases with a hierarchical structure.