Optical behaviour of cholesteric liquid crystal cells with novel photoisomerizable chiral dopants

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.…”

New U-shaped liquid crystals azobenzene derived from catechol for photoswitching properties

“…A photostationary state from trans to cis isomer was reached within approximately 120 s under irradiation at 365 nm [22]. A photochemical switching behavior by means of cholesteric liquid crystals systems containing an azobenzene derivative as a photoisomerizable guest molecule is reported [24,25]. From the results of the investigation, the UV spectra of azo compounds in chloroform show that trans-azo derivatives could be changed to the cis-form in 70 s through UV irradiation and were found to have 12 h thermostability [25].…”

“…The reverse transformation of the Z isomer into the E isomer can be brought by irradiation with visible light (in the range of 400 to 500 nm). This reverse process is known as thermal back relaxation which occurs in the dark and this reverse process (cis to the trans) can occur thermally or photochemically with visible light [20][21][22][23][24][25][26][27].…”

Dynamic gratings in a chiral nematic liquid crystal

“…Chiral nematic LC's have been successfully employed for light modulation due to electrically-controlled optical activity [1,2], switchable diffractive gratings [3] or as the media for dynamic holography with high diffraction efficiency [4,5]. A very low energy is needed for the substantial change of the intrinsic helical pitch when photosensitive chiral additives are used that allowed for efficient colour image recording [6,7], tunable CLC lasers [8,9], light polarisation control [10,11] as well as diffraction grating recording [12].…”