Photochemical tuning capability of cholesteric liquid crystal cells containing chiral dopants end capped with menthyl groups

Abstract

2007) Photochemical tuning capability of cholesteric liquid crystal cells containing chiral dopants end capped with menthyl groups, Liquid Crystals, 34:7, 891-902,In order to investigate the photochemical tuning capability of chiral monomers and polymers containing end-capped menthyl groups, a new series of chiral dopants was synthesized and added to commercially available nematic liquid crystals to induce cholesteric liquid crystal (LC) phases. The addition of chiral dopants with azo structure led to phototunability of the reflection colour of the LC cells. Photochromic variation of the LC cells due to photoisomerization of the azo compound was investigated. After photopolymerization of the monomers inside the cholesteric LC cells, the centre wavelength of the reflected band of the incident light was found to be fixed and the reflected bandwidth was broadened, resulting in a red shift. A schematic representation of both the photoisomerization of the azo dopants and its effect on variation of twisting pitches is proposed. Real image recording was performed using 365 nm UV through a mask with text. The top and side views of the morphological network structures of a fabricated cholesteric LC cell were investigated using scanning electron microscopy. The results of this investigation demonstrated that RGB reflected colours of LC cells can easily be achieved through the addition of the menthylcontaining synthesized chiral compounds to nematic LCs. The addition of synthesized AzoM helped further in recording the patterns onto cholesteric LC films using 365 nm UV exposure.

Photoresponsive Cholesteric Liquid Crystals

“…Taking into account that the molecular shape for cis isomers of 3,3 -disubstituted azobenzenes (rod-like) and 4,4 -disubstituted azobenzenes (bent) is different, these results strongly support the theory that the pitch changes are related to the order parameter affected by the photoisomerization of azobenzene molecules. The multiple dopants system may also contain photoresponsive chiral dopants and non-photoresponsive codopants [32,82,96,97,[105][106][107][108][109][110]. In these systems, the pitch lengths are determined by the HTPs of both dopants, and the photoresponsive dopant has the additional function of photosensitization.…”

Holographic gratings formed in photosensitive polymer materials with a liquid crystalline monomer

“…In another article, it was reported that the steric hindrance and molecular arrangement of chiral segments affect the physical properties of photoresists [19][20][21]. In studying the steric effects on the induction of cholesteric liquid-crystals, we synthesized a series of chiral dopants and chiral monomers [22][23][24].…”

Reversible Reflection Color‐Control in Smectic Liquid Crystal Switched by Photo‐Isomerization of Azobenzene

“…It is well known that reflection colors from the cholesteric phase can be reversibly tuned by external stimuli such as temperature, force, light exposure or electric fields. [4][5][6] In addition, azobenzene photochirals with two chiral centers have been synthesized to control the reflection color. [1] Azobenzene is famous as an excellent photochromic molecule due to its thermal stability, photoreversibility as well as easily resolved isomers.…”

“…Among them, light exposure is particularly attractive due to its advantages of remote, spatial, and temporal control. [4][5][6] In addition, azobenzene photochirals with two chiral centers have been synthesized to control the reflection color. As such, it is not unexpected a much work in the area of dynamic color-control is focused on azobenzene chromophores.…”

“…[3] When the azobenzene-based chiral compounds were capped with menthyl groups, an improved range of nearly 200 nm was observed. [4][5][6] In addition, azobenzene photochirals with two chiral centers have been synthesized to control the reflection color. The team of Li examined an axially chiral bis(azo) chromophore with a large HTP [7] and realized a reversible phototuning of the reflection color across the full visible spectrum by imparting axially chiral azobenzene to an achiral nematic LC host.…”