Design and investigation of de Vries liquid crystals based on 5-phenyl-pyrimidine and (R,R)-2,3-epoxyhexoxy backbone

Area of Science:

• Materials Science
• Organic Chemistry
• Condensed Matter Physics

Background:

• Calamitic liquid crystals are essential for electro-optic devices.
• 5-phenyl-pyrimidine derivatives offer a versatile core for designing novel liquid crystalline materials.
• Understanding phase transitions and molecular behavior is crucial for optimizing liquid crystal performance.

Purpose of the Study:

• To design, synthesize, and characterize novel calamitic liquid crystals based on 5-phenyl-pyrimidine.
• To investigate the influence of terminal siloxane and perfluorinated chains on liquid crystal phases and properties.
• To explore the de Vries smectic characteristics and electro-optic behavior of these new compounds.

Main Methods:

• Synthesis of 5-phenyl-pyrimidine derivatives functionalized with chiral epoxyhexoxy and siloxane/perfluorinated chains.
• Characterization using techniques to determine phase behavior (e.g., DSC, polarized optical microscopy).
• Analysis of layer shrinkage and de Vries coefficient.
• Development of a three-parameter mean-field model for orientational distribution function (ODF).

Main Results:

• The perfluorinated analog exhibits a wide SmA* phase range (82 °C).
• The siloxane analog shows both SmA* and SmC* phases with a weak first-order transition.
• The siloxane analog displays de Vries smectic characteristics (CdeVries ≈ 0.86) with significant layer shrinkage (1.7%).
• The mean-field model successfully reproduces electro-optic properties and predicts an ODF crossover near the SmA*-SmC* transition.

Conclusions:

• Novel 5-phenyl-pyrimidine liquid crystals with tunable properties have been developed.
• The siloxane-based compound exhibits promising de Vries smectic behavior, suitable for specific electro-optic applications.
• The developed mean-field model provides insights into the molecular ordering and electro-optic response of these liquid crystals.