Synthesis and Characterization of Novel Radical Liquid Crystals Showing Ferroelectricity

Abstract

Preparation and characterization of a new series of all-organic ferroelectric liquid crystalline (LC) materials, 4-alkoxyphenyl trans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxyl-2-yl] benzoates (2), which are the structural isomers of the previously reported trans-2-alkoxyphenyl-5-[4-(4-alkoxybenzenecarbonyloxy)phenyl]-2,5-dimethylpyrrolidine-1-oxyls (1) containing a polar and chiral cyclic-nitroxide unit within the rigid core, are described. (2S,5S)- 2 showed ferroelectricity in the SmC* phase, and one of them exhibited a temperature-dependent spontaneous polarization (P _S ) inversion, which was not observed for (2S,5S)- 1.

Keywords:

• Paramagnetic chiral liquid crystals
• smectic liquid crystals
• ferroelectricity
• nitroxyl radical
• spontaneous polarization inversion

Acknowledgment

This work was supported by the Grant-in-Aid for Scientific research (No. 19350067) from Japan Society for the Promotion of Science and the Asahi Glass Foundation (R.T.).

Notes

^b The phase transition is not observed by DSC analysis but by polarizing microscopy.

^c Two peaks are overlapping so that the transition enthalpies are united.

^a Measured at a temperature 2°C below the phase transition form the SmA* phase to the SmC

*phase on the cooling run.

^b Spotaneous polarization.

^c Optical response time required to attain 10–90% of the optical transmittance after field reversal.

^d Viscosity calculated using γ = |Ps| Eτ _{10 − 90}/1.75.

^e Optical tilt angle measured by hot-stage polarized microscopy.