Direct optical switching of bistable cholesteric textures in chiral azobenzene-doped liquid crystals

Abstract

The direct optical switching of bistable cholesteric textures (i.e., planar and focal conic textures) in chiral azobenzene-doped liquid crystals (LCs) is demonstrated. Chiral azobenzene is a chiral dopant with optically tuned helical twisting power that results from the photo-isomerization between trans- and cis- isomers via exposure to UV or visible light. The pitch length of the material can be optically and repeatedly elongated and shortened. With regard to free energy, LCs tend to be stable at planar (focal conic) textures when pitch length is elongated (shortened) by exposure to UV (visible) light. Thus, direct optical switchable LC displays are investigated.

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

“…As shown in Figure 3c, the photodynamic light‐scattering performance accelerated and strengthened along with increasing UV power because of the drop in helical pitch adapting to the excited photon‐density dependence on the photoisomerization ratio of chiral motor (Figure S11a, Supporting Information), as described in previous work 58. Importantly, since the elastic energy of defects, containing lines, loops, and knots, is positively correlated with the pitch length,69, 70, 71 an increasing energy barrier occurs between the free energy of the FC and planar reconfiguration in the photochemical reaction 72, 73. However, the light scattering performance spontaneously degenerated at the low excitation power density (<20.0 mW cm −2 ), as a result of the advantage of the surface anchoring energy of CLCs on the alignment layer over the low energy barrier with a large pitch length 74, 75.…”

Liquid Crystal Display—Present Status and Emerging Technology

“…In recent decade, cholesteric LCs (CLCs), also known as chiral nematic LCs, have been studied by many scientists [18][19][20][21][22][23]. CLCs usually consist of nematics and a chiral dopant, as well as have two stable textures, planar (P) and focal conic (FC) textures.…”

“…12.4b) show strong light scattering because of the randomly arranged helical axes. Such various potential bistable (reflective planar and scattering focal conic states) LCD technologies have been developed because they present low power consumption [22,23].…”

Optically Switchable Circularly Polarization-Dependent Optical Vortex

“…Azobenzene is a kind of material that can change its molecular structure under ultraviolet light (UV) and green light between trans isomer and cis isomer, which has been used for phase transition between blue phase and chiral nematic phase [13,14], and spectra shift [15][16][17][18][19]. Optical switch mechanisms, such as phase transition between blue phase and chiral nematic phase of azobenzene materials, have been explored intensively based on azobenzene materials including azobenzene chiral dopant [16,17], azobenzene liquid crystal [15,[20][21][22], and other azobenzene molecules [13,14,18,19].…”

“…Optical switch mechanisms, such as phase transition between blue phase and chiral nematic phase of azobenzene materials, have been explored intensively based on azobenzene materials including azobenzene chiral dopant [16,17], azobenzene liquid crystal [15,[20][21][22], and other azobenzene molecules [13,14,18,19]. Recently, photo-manipulated photonic bandgap devices based on optically tristable chiral-tilted homeotropic nematic liquid crystal has been demonstrated [23].…”