Dicyanodistyrylbenzene‐Based Chiral Fluorescence Photoswitches: An Emerging Class of Multifunctional Switches for Dual‐Mode Phototunable Liquid Crystals

Two novel enantiomeric chiral fluorescence photoswitches containing two chiroptical ( S )‐(−)‐ or ( R )‐(+)‐1,1′‐bi‐2‐naphthol covalently bonded to a central dicyanodistyrylbenzene unit are facilely synthesized and efficiently used to construct an optically tunable reflective‐photoluminescent cholesteric liquid crystal (LC) device. In comparison with conventional azobenzene‐based devices, this new class of chiral photoswitches is found to undergo unprecedented irreversible Z/E photoisomerization in both organic solvent and LC media upon irradiation of 365 nm ultraviolet (UV) light. The isomers on the photostationary state and even the intermediate states after Z/E photoisomerization do not exhibit thermal relaxation behavior and thus are stable in a dark environment. The photo‐induced Z/E photoisomerization leads to a large change in the helical twisted power of the chiral switches, enabling a reflection spectral shift of more than 1500 nm in the cholesteric LC. These structural modifications also produce a pronounced fluorescence spectral variation, which makes it possible to simultaneously phototune both the reflection and the fluorescence in the cholesteric LC. We also present proof‐of‐principle demonstrations of the fact that the phototuning of the cholesteric LC based on the chiral fluorescence photoswitches can be used in irreversible UV light indicators and reflective–photoluminescent LC display devices.