Reversible Handedness Inversion and Circularly Polarized Light Reflection Tuning in Self-Organized Helical Superstructures Using Visible-Light-Driven Macrocyclic Chiral Switches

A series of macrocyclic azobenzene-based chiral photoswitches have been judiciously designed, synthesized, and characterized. In the molecular structures, binaphthyl is covalently linked to ortho-positions of azobenzene, and four different substituents are linked to 6,6 '-positions of binaphthyl. The photoswitches show enhanced helical twisting power (HTP) when doping in commercially available achiral liquid crystals to form self-organized helical superstructures, i.e., cholesteric liquid crystals (CLCs). All the photoswitches exhibit reversible photoisomerization driven by visible light of different wavelengths in both organic solvent and liquid crystals. The photoswitches with shorter substituents enable handedness inversion of CLCs upon photoisomerization. These are the first examples of ortho-linked azobenzene-based photoswitches that enable handedness inversion in CLCs. The photoswitches with longer substituents display only HTP values decreasing while maintaining the same handedness.

Automated summary

A series of macrocyclic azobenzene-based chiral photoswitches have been designed, synthesized, and characterized. The photoswitches, when doped in achiral liquid crystals, exhibit enhanced helical twisting power and form self-organized helical superstructures called cholesteric liquid crystals. Reversible photoisomerization can be achieved by visible light, and the photoswitches with shorter substituents enable handedness inversion of the liquid crystals. This is the first example of ortho-linked azobenzene-based photoswitches that enable handedness inversion in cholesteric liquid crystals.