Large Thermally Irreversible Photoinduced Shift of Selective Light Reflection in Hydrazone‐Containing Cholesteric Polymer Systems

Abstract

Stimuli responsive liquid crystalline polymers are a unique class of so‐called “smart” materials demonstrating various types of mesomorphic structures easily controlled by external fields, including light. In the present work we synthesized and studied a comb‐shaped hydrazone‐containing copolyacrylate exhibited cholesteric liquid crystalline properties with the pitch length of the helix being tuned under irradiation with light. In the cholesteric phase selective light reflection in the near IR spectral range (1650 nm) was measured and a large blue shift of the reflection peak from 1650 nm to 500 nm was found under blue light (428 or 457 nm) irradiation. This shift is related to the Z‐E isomerization of photochromic hydrazone‐containing groups and it is photochemically reversible. The improved and faster photo‐optical response was found after copolymer doping with 10 wt % of low‐molar‐mass liquid crystal. It is noteworthy that both, the E and Z isomers of hydrazone photochromic group are thermally stable that enable to achieve a pure photoinduced switch without any dark relaxation at any temperatures. The large photoinduced shift of the selective light reflection, together with thermal bistability, makes such systems promising for applications in photonics.

P‐190: Photo‐triggered Transmission‐color Through a Cholesteric Liquid Crystal for Multi‐level Information Encryption

“…Among these stimuli, optically driven CLCs in accordance with the light field facilitating localized reflection have spatial advantages for the capability of electric-free remote control [1] and local control. Photochrome isomerization of dye molecules are used to generate the driving force to tune pitch, subsequently modulate the reflection colors [2][3][4][5][6][7][8]. These days, the printed CLCs droplets are also investigated by depositing picolitres of nematic LC droplets into short-pitch CLC droplets using dropon-demand inkjet printing [9].…”

Temperature Self-Adaptive and Color-Adjustable Smart Window Based on Templated Cholesteric Liquid Crystals

“…CLCs are excellent candidates for application in many fields, such as displays, sensors, and filters, due to unique twist structures [ 1 , 2 , 3 , 4 , 5 , 6 ]. Their dynamic response to external stimuli, such as heat, light, or electricity, makes them attractive in smart windows [ 7 , 8 , 9 , 10 , 11 ]. Compared with traditional windows, smart windows enable dynamic regulation of daylighting, which is conducive to thermal management, energy consumption reduction, and color adjustment for humans [ 12 , 13 , 14 , 15 , 16 , 17 ].…”