Photoregulation of the Chiral Nematic Phase by Using a Hexa-Arylazopyrazole-Substituted Co(III) Complex

Area of Science:

• Coordination Chemistry
• Materials Science
• Photochemistry

Background:

• Photoresponsive materials offer dynamic control over material properties.
• Liquid crystals are widely used in displays and optical devices.
• Chiral dopants are essential for inducing specific liquid crystal phases.

Purpose of the Study:

• To synthesize and characterize a photoresponsive Cobalt(III) complex.
• To investigate its ability to induce and modulate the chiral nematic phase in liquid crystals.
• To evaluate its potential for optical applications.

Main Methods:

• Synthesis and isolation of Λ- and Δ-enantiomers of a hexa-arylazopyrazole-substituted tris-(β-diketonato) Co-(III) complex.
• Photoisomerization studies using UV and visible light (E/Z isomerization).
• Doping of the liquid crystal MBBA with the Co-(III) complex and characterization of the induced chiral nematic phase.

Main Results:

• The Co-(III) complex exhibits reversible E/Z photoisomerization upon irradiation with UV and visible light.
• The complex effectively induces a chiral nematic phase in MBBA at low concentrations.
• Photoisomerization leads to significant reversible modulation of the helical pitch and high helical twisting power (HTP).
• HTP values ranged from 615 to 346 μm⁻¹ (P helix) and -563 to -352 μm⁻¹ (M helix) at 30 °C.

Conclusions:

• The synthesized Co-(III) complex is a highly effective photoresponsive dopant for liquid crystals.
• It enables precise, light-induced control over the helical pitch and HTP.
• Its ability to induce chiral nematic phases at low concentrations makes it promising for advanced optical devices.