Columnar liquid crystal with a spontaneous polarization along the columnar axis

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Liquid Crystals

Background:

• Molecular self-assembly is key to creating advanced materials.
• Liquid crystals exhibit unique phases between solid and liquid states.
• Macroscopic polarization in soft materials is challenging to achieve.

Purpose of the Study:

• To design and synthesize a fan-shaped molecule capable of self-assembly.
• To investigate the liquid crystalline properties of the self-assembled material.
• To explore the optical properties, specifically second harmonic generation (SHG), of the polar mesophase.

Main Methods:

• Synthesis of a fan-shaped molecule with hydrogen-bonding amide groups and a polar aromatic core.
• Characterization of the self-assembled structure using techniques like X-ray diffraction and microscopy.
• Measurement of macroscopic polarization along the columnar axis.
• Optical measurements of second harmonic generation (SHG) during phase transitions.

Main Results:

• The fan-shaped molecule self-assembles into a columnar liquid crystalline mesophase.
• This mesophase exhibits unprecedented spontaneous macroscopic polarization along the columnar axis.
• The polar mesophase shows a significant second harmonic generation (SHG) signal.
• The SHG signal disappears upon transition to an isotropic melt and is recovered upon cooling.

Conclusions:

• Fan-shaped molecules with specific functional groups can form polar liquid crystalline phases.
• Spontaneous macroscopic polarization in liquid crystals can be achieved through molecular design.
• The observed SHG signal confirms the polar nature of the mesophase and its potential for nonlinear optical applications.