Effect of lateral methoxy substitution on mesomorphic and structural properties of ferroelectric liquid crystals

Abstract

A new series of materials with a chiral fragment derived from lactic acid and a methoxy group as lateral substituent in different positions of the molecular core was synthesised and investigated. Derivatives with ester or ether linkages of the non‐chiral chain were also studied. Depending on the molecular structure, cholesteric, twist grain boundary smectic A (TGBA*), chiral smectic A (SmA*) or chiral smectic C (SmC*) phases were detected. In derivatives with the ester linkage and a methoxy group at the nearest and the next nearest phenyl ring to the non‐chiral chain these phases completely disappear. On the other hand, a methoxy group on the phenyl ring close to the chiral chain provides a compound with low layer shrinkage at the SmA*–SmC* phase transition (“de Vries” behaviour). The temperature dependence of the spontaneous polarisation, the tilt angle, the layer spacing as well as the complex permittivity were studied and the results discussed in terms of molecular structure.

Keywords:

• ferroelectric liquid crystal
• chiral materials
• methoxy substituent
• layer shrinkage
• X‐ray diffraction
• dielectric properties
• spontaneous polarisation

Acknowledgements

This work is supported by the German–Czech bilateral programme DAAD (German Academic Exchange Service)–ASCR (Academy of Science of the Czech Republic) No. D11‐CZ7/06‐07 & D7‐CZ8/08‐09 and also partially by projects No. IAA100100710 from the Grant Agency of the Academy of Sciences of the Czech Republic, No. 202/05/0431 from the Czech Science Foundation and No. AVOZ10100520. Authors (A.B. and V.N.) greatly acknowledge Dr. S. Bezner and Dr. C. Hägele for help with the SAXS measurements.