Observation of a chiral smectic C phase over a wide thermal range with novel phase sequences in rigid, bulky chiral dimers

Abstract

Four new, non-symmetric, optically active, liquid crystal dimers in which cholesterol and three-ring salicylaldimine mesogenic cores are interlinked through a flexible even-parity (ω-oxyalkanoyloxy) spacer have been synthesized and characterized by polarising optical microscopy, differential scanning calorimetry, electrical switching and X-ray diffraction. All the dimers, which differ from each other in the lengths of the central spacers (n = 3 and 5) and the terminal alkoxy chains (m = 20 and 22), exhibit a thermodynamically stable chiral smectic C phase over an unprecedented (100–180 °C) thermal range in novel phase sequences. Notably, the electrical switching study suggests the ferrielectric nature of the chiral smectic C phase originating arguably due to equally strong competition between ferroelectric and antiferroelectric ordering. The occurrence of such a mesophase in mesogens synthesized in this study is especially noteworthy as they comprise a bulky, rigid cholesterol entity.