Efficient visible-light full-color tuning of self-organized helical superstructures enabled by fluorinated chiral switches

Abstract

Light-driven chiral switches have the ability to tune and control the self-organized helical superstructures of cholesteric liquid crystals (CLCs), resulting in the photo-induced reflection wavelength shift of the CLCs. A new type of axially chiral switch functionalized with fluorine atoms ortho to the azobenzene moiety is found to exhibit reversible visible-light-driven photoisomerization due to a separation of the n–π* absorption bands of the trans and cis isomers. These chiral switches all have high HTP values and the doped CLCs with 15.8 wt% concentration demonstrates reversible dynamic tuning of the reflection color within the entire visible spectrum driven by 530 nm and 445 nm visible light. It is also noteworthy that the thermal stability is improved thanks to the cis form of the fluorinated azobenzenes possessing a remarkably long half-life. The newly designed visible-light-driven chiral switches may broaden the application of CLCs, especially in the fields where high energy UV light is unfavorable.