1,2,4-oxadiazole-based bent-core liquid crystals with cybotactic nematic phases

Area of Science:

• Liquid Crystal Physics
• Materials Science
• Organic Chemistry

Background:

• Bent-core mesogens and polycatenar molecules are advanced liquid crystal materials.
• Understanding their mesomorphic behavior is crucial for developing new electro-optical devices.

Purpose of the Study:

• To synthesize and investigate the mesomorphic properties of novel bent-core mesogens and polycatenar molecules.
• To explore the influence of molecular structure on phase behavior and physical properties.

Main Methods:

• Synthesis of diphenyl-1,2,4-oxadiazole-based bent-core mesogens and polycatenar molecules.
• Characterization using polarizing microscopy, differential scanning calorimetry, X-ray diffraction (XRD), dielectric, electro-optical, and second-harmonic generation (SHG) experiments.

Main Results:

• Most compounds exhibited broad regions of skewed cybotactic nematic (NcybC) and tilted smectic (SmC) phases with significant core tilt (up to 63°).
• Non-tilted SmA and NcybA phases were observed in a compound with a single terminal chain.
• XRD patterns indicated 2D periodicity in nematic phases, suggesting short correlation lengths.
• Nematic phases displayed local polar order with dielectric reorientation of polar domains.
• Chiral nematic phases (NcybC*) were obtained with chiral tails, but blue phases were not observed.

Conclusions:

• The synthesized bent-core mesogens and polycatenar molecules exhibit diverse mesomorphic behaviors, including NcybC and SmC phases.
• The nematic phases possess local polar order and exhibit dielectric reorientation.
• Molecular structure, particularly terminal chains, significantly influences phase behavior and tilt angles.