Mesophases of hockey stick mesogens

Abstract

Enantiotropic anticlinic smectic C (SmC_a), smectic C (SmC), smectic A (SmA) and nematic (N) phases of hockey stick molecules were obtained by tuning the length of hydrocarbon chain located at the meta‐position to the carbon–carbon double bond of a stilbenyl moiety of calamitic mesogenic skeletons. The thermodynamic properties and some aspects of optical appearance of these phases are indiscernible from those of calamitic mesogens. Distinctions are noted such as the appearance of two‐brush defects and two types of domains in the tilted smectic phases. X‐ray results indicate the existence of clusters in the nematic phase and simple layer structure in the smectic phases. These phases exhibit electric field driven colour switching, and all the results imply that all three molecular axes are simultaneously aligned in the N and SmC phases, a behaviour unprecedented and different from those of conventional calamitic mesogens. Doping with a chiral calamitic mesogen results in formation of corresponding chiral N and ferroelectric SmC phases, but the effect for the SmC_a phase is not clear. Small and comparable values of spontaneous polarisation are obtained for the doped and non‐doped phases. Molecular organisations of the SmC and SmCa phases are proposed and discussed.

Keywords:

• hockey stick molecule
• synclinic phase
• anticlinic phase
• chiral dopant
• ferroelectric phase
• antiferroelectric phase

Acknowledgements

This work was supported by the National Science Council contract numbers NSC96‐2113‐M‐032‐001 and NSC94‐2113‐M‐032‐005. Parts of the electric studies were conducted at the Department of Polymer Engineering of NTUST Taiwan. J.Y. Lee and H. H. Liang are gratefully acknowledged.