Chiral Nematic Polymer Mixture Containing Crosslinker and Photosensitive Chiral Dopant: New Type of Materials with Tunable Photo-Optical Properties

Abstract

A cholesteric mixture based on a menthyl‐containing copolymer, photosensitive chiral dopant, mesogenic diacrylate, and photoinitiating agent has been prepared. The mixture shows a selective light reflection in the visible light spectral region. The action of UV irradiation (313 or 365 nm) on the planar‐oriented films generates the occurrence of two parallel processes: E/Z (i.e., cis–trans) photoisomerization of the chiral dopant and photopolymerization of the diacrylate. The first process leads to the untwisting of the cholesteric helix and shifts the selective light‐reflection maximum to the long‐wavelength spectral region, whereas the second process leads to the development of a polymer network that fixes the helical supramolecular structure. As a result of a simultaneous occurrence of the two above‐mentioned processes, the shift in the selective light‐reflection maximum is thermally irreversible, even though the Z/E isomerization of the chiral dopant itself can be reversed by annealing. On irradiation with visible light (>450 nm), the dopant experiences the E/Z isomerization but photopolymerization is absent because the photoinitiator shows no absorption in this spectral region. In this case, the shift in the selective light‐reflection maximum can be reversed to its initial value by annealing, whereby the original helix pitch is recovered. The kinetic features of helix untwisting at different temperatures and light wavelengths were studied. The experimental data obtained in this work allow one to conclude that the as‐prepared mixture presents a new multifunctional material with “tunable” photo‐optical properties and may be used for recording and storage of optical information.

Controlling the Color of Cholesteric Liquid‐Crystalline Films by Photoirradiation of a Chiroptical Molecular Switch Used as Dopant

“…Recently, a polymeric LC system was reported where switching an azobenzene dopant was accompanied by crosslinking of the polymeric LC due to the presence of a diacrylate and a polymerization initiator. [19] This resulted in simultaneous switching and crosslinking from a polymeric LC state showing an approximately 645 nm reflection, to a crosslinked state maximally showing an approximately 750 nm reflection. In an approach comparable to our approach reported in this article, the authors make elegant use of the simultaneously occurring light-induced switching and crosslinking, but only red colored liquid-crystalline and crosslinked samples were obtained.…”

Synthesis, Liquid‐Crystalline Properties, and Photo‐optical Studies of Photoresponsive Oligomeric Mesogens as Dopants in a Chiral Glassy Liquid Crystal

“…[3,4] The sensitivity of ChLCs to external parameters, such as temperature, the presence of impurities, and light, has led to many practical applications and has been the subject of much theoretical research. [2,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Several mechanisms have been proposed to explain the role that the dopant molecules play in the modulation of the macroscopic chirality of ChLCs. [11,[24][25][26][27][28] Recently, we reported that the mechanism of the helical-pitch shift that is induced by achiral dopants (as well as in dimesogenic compounds) is due to enhancement of smectic A (SmA)-like clusters in the cholesteric phases.…”

Photo-Thermal Modulation of Cholesteric Liquid Crystals with a Dual Circularly Polarized Light Reflection Band

“…Among these, the change in the helical pitch caused by photochemical reactions in the Ch-LCs is especially of interest [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. Azobenzene is a typical photochromic compound, which changes its molecular shape upon photoirradiation.…”