Fluorenone imidazolium salts as novel de Vries materials

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Liquid Crystals

Background:

• Tilted mesophases, such as the SmC phase, are essential for electro-optic devices but are rare in ionic liquid crystals (ILCs).
• Developing ILCs with SmC phase behavior is critical for advancing display and photonic technologies.

Purpose of the Study:

• To design and synthesize novel ILCs capable of forming the SmC phase.
• To investigate the de Vries-like behavior in these newly synthesized ILCs.
• To understand the influence of molecular structure on mesomorphic properties and phase transitions.

Main Methods:

• Synthesis and characterization of a library of ILC derivatives, ImR(On,Ym)X, featuring a fluorenone core, flexible spacer, and imidazolium head group.
• Mesomorphic properties were studied using differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD).
• Temperature-dependent small-angle X-ray scattering (SAXS) and POM were used to measure smectic layer spacing and optical tilt angles.

Main Results:

• The synthesized ILCs ImR(On,Ym)X successfully exhibited SmA-SmC phase transitions.
• Maximum layer contraction values ranged from 0.4% to 2.1%, with a lowest reduction factor (R) of 0.2 observed for Im(O12,S14)Br.
• Electron density calculations suggested a bilayer structure, and temperature-dependent emission studies indicated self-assembly influences emission intensity.

Conclusions:

• A novel design concept successfully induced the SmC phase and de Vries-like behavior in ionic liquid crystals.
• The synthesized ILCs demonstrate tunable mesomorphic properties suitable for electro-optic applications.
• Molecular design and self-assembly play significant roles in the properties and performance of these functional ILCs.