Title: Photostationary RGB Selective Reflection from Self-Organized Helical Superstructures for Continuous Photopatterning

Author: Lang Qin, Jia Wei, Yanlei Yu*

Journal: Adv. Optical Mater., 2019, 7(18), 1900430.

Abstract:

Light-driven cholesteric liquid crystals (CLCs) are intriguing materials due to the dynamic tuning of their selective reflection, which originates from self-organized helical superstructures, in response to light. However, CLC systems are restricted to displaying static optically addressed images and need to be initialized or refreshed before every new image can be displayed. Herein, a novel tuning mechanism based on a partial photochemical phase transition is proposed to enable continuous patterning of photostationary red, green, and blue (RGB) colors in a CLC system, which contains nonresponsive chiral dopants and o-fluoroazobenzenes (Fazo) to serve as the photoswitch. Distinct isomer ratios of Fazo result in precise light-directed RGB colors for the photostationary states, and, thus, a fixed relationship is established between the light stimulus and the reflection color. Accordingly, the RGB color patterns can be continuously erased and rewritten under light irradiation with different wavelengths. A photocontrollable “Tetris game” is demonstrated for the first time according to the programmable modulation of the CLC reflection, providing a new concept for optically rewritable displays.

Fulltext Link: https://onlinelibrary.wiley.com/doi/10.1002/adom.201900430

Herein, we report a new and straightforward strategy to program the reflection of cholesteric liquid crystals (CLCs) for continuous patterning of RGB colors based on a novel partial photochemical phase transition mechanism in the CLCs rather than through HTP variation. We separated a commonly used photoresponsive chiral switch into two independent simple structures, including a binaphthyl derivative as the chiral dopant and Fazo as the photoswitch. When doped into the LC host E7, the binaphthyl derivative immediately induced helical superstructures, and Fazo underwent conformational changes upon photoisomerization, disturbing the LC alignment and tuning the reflection color. Fazo of distinct isomer ratios (trans/cis) of 75/25, 50/50, and 20/80 contributes to the full-color tuning in the visible spectrum and light-directed modulation of the three primary RGB colors. Based on this programmable modulation of the CLC reflection, RGB color patterns can be continuously erased and rewritten under irradiation with different wavelengths. Furthermore, we demonstrated colorful patterns and even a photocontrollable “Tetris game”.