Odd-even effects in bent-core compounds containing terminal n-alkyl carboxylate groups

Area of Science:

• Materials Science
• Organic Chemistry
• Condensed Matter Physics

Background:

• Bent-core liquid crystals are a unique class of materials with potential applications in advanced optical devices.
• Symmetrical bent-core compounds with terminal alkyl carboxylate groups offer tunable properties based on molecular structure.
• Understanding structure-property relationships is crucial for designing novel liquid crystalline materials.

Purpose of the Study:

• To synthesize and characterize a homologous series of five-ring symmetrical bent-core compounds.
• To investigate the dielectric and electro-optical properties of these compounds.
• To explore the influence of alkyl chain length on mesophase behavior and phase transitions.

Main Methods:

• Synthesis of eleven five-ring symmetrical bent-core compounds with varying terminal alkyl carboxylate chain lengths.
• Characterization using techniques such as NMR spectroscopy and differential scanning calorimetry.
• Investigation of dielectric and electro-optical properties, including phase transitions and switching behavior.

Main Results:

• Lower homologues (n=6-11) exhibited B structures with an odd-even effect in director tilt and polar arrangements, attributed to steric factors.
• Three middle homologues displayed a bistable B' phase with linear electro-optical switching, transitioning to a chiral antiferroelectric smectic phase.
• Higher homologues (n=16, 18) exclusively showed the B' phase.

Conclusions:

• The study demonstrates a significant odd-even effect in the mesophase behavior of symmetrical bent-core liquid crystals.
• The observed B' phase exhibits bistability and linear electro-optical switching, highlighting potential for display applications.
• Molecular structure, specifically alkyl chain length, critically influences the phase behavior and electro-optical response of these materials.