New Pyrazolium Salts as a Support for Ionic Liquid Crystals and Ionic Conductors

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Physical Chemistry

Background:

• Ionic liquid crystals (ILCs) integrate properties of liquid crystals and ionic liquids.
• ILCs are explored for their potential in creating conductive materials within ordered systems.
• Understanding the relationship between molecular structure and mesophase behavior is crucial for designing functional ILCs.

Purpose of the Study:

• To synthesize and characterize novel ionic liquid crystals (ILCs) with pyrazolium cations and various anions.
• To investigate the thermal behavior and mesophase characteristics of these newly synthesized ILCs.
• To explore the influence of mesophase structure on ionic conductivity.

Main Methods:

• Synthesis of five new families of ILCs with varying alkyl chain lengths and anions (Cl⁻, BF₄⁻, ReO₄⁻, PTS, OTf).
• Thermal analysis using polarized light optical microscopy (POM) and differential scanning calorimetry (DSC).
• Structural characterization via X-ray diffraction (XRD) and dielectric property measurements.

Main Results:

• ILCs with Cl⁻, BF₄⁻, ReO₄⁻, and PTS anions exhibited thermotropic mesomorphism, forming lamellar mesophases.
• POM and XRD confirmed the lamellar structure, consistent with the crystal structure of a representative ILC.
• Dielectric studies revealed that the mesophase arrangement enhances ionic mobility and conductivity, particularly in mesomorphic salts.

Conclusions:

• The synthesized pyrazolium-based ILCs, excluding those with OTf anions, display thermotropic lamellar mesomorphism.
• The ordered supramolecular structure of the mesophases significantly promotes ionic mobility and conductivity.
• These findings highlight the potential of ILCs for applications requiring ordered, conductive materials.