3-Hydroxycinnamic acid – a new central core for the design of bent-shaped liquid crystals

Abstract

The synthesis and mesomorphic properties of a new series of bent-shaped liquid crystals based on 3-hydroxycinnamic acid are presented. Prepared compounds differ in the orientation of an ester linking group in one of the side arms. Additionally, the mesomorphic properties have been tuned by employing either an alkoxy or carboxylic terminal group and by varying the length of terminal alkyl chains. Texture observation and calorimetric studies, as well as electro-optics, X-ray and dielectric measurements have been performed. Influence of the ester linking group orientation and the length of the terminal alkyl chain on mesomorphic behaviour has been established. Out of 12 studied compounds only one formed lamellar phases, namely the B2–B5 phase sequence, while all other exhibited columnar phases, either B1 or B1Rev type, depending on the direction of the ester group. Structural properties of the columnar phases have been studied in detail using X-ray diffraction techniques for pure materials as well as for binary mixtures of compounds forming the B1 and B1Rev phase. All results are discussed with respect to the molecular structure.