Color Tuning in Ferroelectric Nematic Liquid Crystals using Triptycene/Hydrazone Chiral Photoswitches

Area of Science:

• Liquid Crystal Physics
• Materials Science
• Photochemistry

Background:

• Ferroelectric nematic liquid crystals (N_FLCs) offer unique electro-optic properties.
• Controlling N_FLC properties with external stimuli is crucial for advanced applications.
• Photoresponsive materials enable light-based tuning of material characteristics.

Purpose of the Study:

• To develop photoresponsive chiral ferroelectric nematic liquid crystals (N_F^*LCs).
• To achieve multi-stimuli control over N_F^*LC properties using light.
• To investigate the impact of photoisomerization on helical twisting power and reflection color.

Main Methods:

• Incorporation of chiral triptycene/hydrazone-based bistable photoswitchable dopants into a polar liquid crystal mesogen (DIO).
• Utilizing UV (340 nm) and visible (442 nm) light irradiation to induce Z→E and E→Z photoisomerization of the dopants.
• Measuring helical twisting power and observing reflection color changes.
• Applying alternating current (AC) electric fields to confirm ferroelectricity.

Main Results:

• Propeller-like dopants exhibited high helical twisting powers (13.5 µm^-1 in DIO).
• Helical twisting power increased to 31.0 µm^-1 upon 442 nm light-induced Z→E photoisomerization.
• Reflection color tuned across the visible spectrum (NIR to blue) at 50 °C.
• Reversible color tuning achieved via 340 nm light-induced E→Z photoisomerization.
• Ferroelectric nature confirmed by light-induced azimuthal deformations under AC electric field.

Conclusions:

• Photoresponsive chiral ferroelectric nematic liquid crystals (N_F^*LCs) were successfully developed.
• Light-induced isomerization provides a powerful method for tuning N_F^*LC properties, including helical twisting power and reflection color.
• These findings open avenues for multi-stimuli responsive liquid crystal devices.