Study of Chiral Dimesogens: Liquid Crystalline Properties, Effect of Smectic Cybotactic Domains in Controlling the Chiral Reflections and Glassy Liquid Crystal Forming Properties

Abstract

Liquid crystalline properties, temperature dependent reflection studies and glassy liquid crystal forming properties of azobenzene/alkylazobenzene containing cholesterol dimesogens with varying methylene spacers have been described. All these compounds exhibit chiral nematic phases, and both chiral nematic and smecticA phases have been observed for the dimesogens containing 4-alkylazobenzene moieties. X-ray diffraction studies in the smecticA phases of these dimesogens show that both monolayer and intercalated arrangements co-exist in the meso phase. Selective reflection observed in the chiral nematics was found to be red shifted upon lowering the temperature due to fluctuations in smectic order. By rapid cooling of the 4-alkylazobenzene compounds from the cholesteric phase transition temperature to 0°C, solid films maintaining a helical molecular order were obtained.

Keywords:

• chiral dimesogens
• glassy liquid crystals
• selective reflection
• smectic cybotactics

Notes

^a Transition temperatures are obtained from DSC analysis at a rate of 5°C min⁻¹ in the first heating and cooling cycles.

^b Cr = crystalline, N* = cholesteric, SmA* = smecticA and Iso = Isotropic.

^c Observed from polarizing optical microscope.