Abstract
The dependence of the helical pitch of a cholesteric liquid crystal based on a composite photosensitive chiral dopant (cChD) on the intensity of light irradiation was studied. The transmission spectra and the selective reflection spectra of cholesteric liquid crystal cells were measured. The concentration of the cChD additive is calculated, so that the peak of selective reflection and its rearrangement occurs in the visible range of the electromagnetic radiation spectrum (380-780 nm). The possibility of photo-control by shifting the peak of the selective reflection of the cChD additive was studied, when exposed to LEDs with wavelengths of 365 nm and 450 nm, while reducing or increasing the intensity, a change in the spiral pitch was observed. Depending on the light intensity, part of the molecules of the chiral additive containing the azo group underwent isomerization, i.e. molecules in the trans-form passed to the cis-form, which led to a spectral shift of the selective reflection peak. If a small intensity of the 365 nm LED was applied, then some of the molecules were forced to transition from the trans- to the cis-form, and then, when illuminated with a 450 nm LED, from the cisto the trans-form. After reversible rearrangement, the properties of cholesteric liquid crystal changes due to interaction with light, because under the influence of light, the equilibrium ratio of the trans- and cis-isomers of the molecules of the substance changed, which macroscopically changed the torsion force of the chiral additive. Using two LEDs of 365 nm and 450 nm with different emission spectra, a reversible control of the cChD selective reflection peak in the visible range was obtained. The maximum displacement occurred at approximately 145 nm.
Highlights
The non-display applications of liquid crystals (LC) for novel LC based devices is the current trend of the LC device technology
Typical cholesteric liquid crystal is achiral nematic liquid crystal mixture doped with a chiral dopant, which ensures the selforganization of the chiral structure of LC molecules
The photosensitive ChLC mixture was obtained by doping nematic LC mixture MLC-6809000, (Merck, Germany) with composite chiral dopant, (IChNM NAS Belarus) that comprises non-photosensitive and photosensitive chiral dopants with the same sign of the helical twist
Summary
The non-display applications of liquid crystals (LC) for novel LC based devices is the current trend of the LC device technology. Сholesteric liquid crystals (ChLC) are chiral materials possessing unique property of selective reflection in the visible spectral range, are in focus of the R&D interest due to their ability to change the distribution of LC molecules under the action of external influences [1] such as temperature [2], light [3], electric field [4] and etc. Planar LC cells are applied to achieve vertical orientation of the ChLC helix and obtain homogeneous structure that does not scatter light [5].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
