Light-Driven Liquid Crystalline Materials: From Photo-Induced Phase Transitions and Property Modulations to Applications

Abstract

Light-driven phenomena both in living systems and nonliving materials have enabled truly fascinating and incredible dynamic architectures with terrific forms and functions. Recently, liquid crystalline materials endowed with photoresponsive capability have emerged as enticing systems. In this Review, we focus on the developments of light-driven liquid crystalline materials containing photochromic components over the past decade. Design and synthesis of photochromic liquid crystals (LCs), photoinduced phase transitions in LC, and photoalignment and photoorientation of LCs have been covered. Photomodulation of pitch, polarization, lattice constant and handedness inversion of chiral LCs is discussed. Light-driven phenomena and properties of liquid crystalline polymers, elastomers, and networks have also been analyzed. The applications of photoinduced phase transitions, photoalignment, photomodulation of chiral LCs, and photomobile polymers have been highlighted wherever appropriate. The combination of photochromism, liquid crystallinity, and fabrication techniques has enabled some fascinating functional materials which can be driven by ultraviolet, visible, and infrared light irradiation. Nanoscale particles have been incorporated to widen and diversify the scope of the light-driven liquid crystalline materials. The developed materials possess huge potential for applications in optics, photonics, adaptive materials, nanotechnology, etc. The challenges and opportunities in this area are discussed at the end of the Review.

Synthesis and Characterization of Photo-Responsive Thermotropic Liquid Crystals Based on Azobenzene

“…Compound 3a-c was synthesized in accordance with the literature and our previous works. Data are not shown here [17][18][19][20][21].…”

“…As we know, the properties of an LC depend on the chemical structure of the azobenzene and other segments [18]. With those objects in mind, we designed and synthesized a new series of azobenzene LC compounds, containing a flexible chain of C m H 2m (where m = 4-12).…”

Stimuli‐Directed Dynamic Reconfiguration in Self‐Organized Helical Superstructures Enabled by Chemical Kinetics of Chiral Molecular Motors

“…Light‐driven dynamic self‐organized helical superstructures, i.e., cholesteric liquid crystals (CLCs), could be obtained upon doping the chiral molecular motors into achiral LC hosts, where the orientation of helical axes is typically expressed as three configurations: (1) parallel to the substrate with a fingerprint texture (lying helixes) resulting from the periodical helical pitch ( p ) defined as the distance as the molecular rotation by 360° twist along the helical axis; (2) perpendicular to the substrate with a Grandjean texture (standing helixes) performing unique Bragg reflection of circularly polarized light at wavelength λ = np , where n is the average refractive index of LC; (3) spatial disorder alignment with a focal conic (FC) texture, which can strongly scatter incident light. Accordingly, light‐directed dynamic control over the helical axes as well as the helical pitch in one, two and three dimensions has been a burgeoning area for promising applications, including photodynamic photonic crystals, tunable mirrorless lasers, holographic microlenses, and light‐directed diffraction gratings 15, 16, 17, 18, 19, 20, 21…”

Synthesis and mesophase behaviour of branched azobenzene-based supramolecular hydrogen-bonded liquid crystals

“…Therefore, the azobenzene moiety is the most widely used photoactive bistable group whether in a rod-shaped [19] or bent-core-shaped mesogen [20,21] because of its easy synthesis and having a good compatibility with LC phase especially in its trans-form (its elongated structure). Depending on the trans-cis transformation of azobenzene, extensive works have been performed to control the orientation of LC, such as inducing nematic phase [18], smectic phase [22], cubic phases [23], adjusting the reflection wavelength of the chiral nematic (N*) phase [24][25][26][27] or Bragg reflection of BPs [28][29][30][31][32][33], phase transitions from nematic to isotropic states [34] and the helical twisting power [35,36]. However, azo compounds usually have relatively high melting point and low solubility in liquid crystals matrix, which has been one of the obstacles to their potential applications.…”