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Chiral Liquid Crystal Trimer Exhibiting an Optically Uniaxial Smectic Phase with a Double-Peak Polarization
Ist Teil von
Journal of physical chemistry. C, 2012-04, Vol.116 (15), p.8678-8687
Ort / Verlag
Columbus, OH: American Chemical Society
Erscheinungsjahr
2012
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
We prepared a chiral liquid crystal trimer consisting of three different mesogenic units connected via flexible spacers with different parity. We then investigated its liquid crystalline properties using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). A POM study revealed that the trimer has a phase sequence of isotropic liquid–optically uniaxial smectic A (SmA*)–helical smectic C (SmC*) on cooling. However, XRD measurements revealed a discontinuous decrease in layer spacing occurring at T – T IA* = −4 K in the SmA* phase. Double-peak polarization in the current response and tristable switching were observed in the low-temperature SmA* phase below T = T IA* – 4 °C. In a binary phase diagram of the trimer and its enantiomer, the transition temperature from the low-temperature SmA* phase to the SmC* phase increased continuously with decreasing optical purity. The results indicate that the low-temperature SmA* phase forms an optically uniaxial structure in which the molecules tilt to the same direction in each layer, as they do in the SmC phase. We discuss the organization of the supermolecules in the unusual smectic phase.