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C3-Symmetric Photoresponsive Chiral Dopants Based on Tribenzotriquinacene
Doping cholesteric liquid crystals (CLCs) with photoresponsive chiral molecules is an effective strategy for devising responsive soft materials, as it allows for the phototuning of the noncovalent interactions in the CLCs, and hence, their helical pitch and optical properties. Here we describe the use of tribenzotriquinacene-based (TBTQ) hydrazone and azobenzene chiral dopants in the modulation of the helical pitch of the LC host, 5CB. The unique C3-symmetry of the TBTQ scaffold enhances the noncovalent interactions with the host and thus the chiral information transfer, resulting in helical twisting power (β) values as high as 147 μm–1. Notably, the TBTQ hydrazone exhibits an unusual deviation from trends observed so far in previous studies, resulting in larger β values for the Z isomer rather than the E one. Moreover, the overall β values for the hydrazone-based dopants are unexpectedly higher than those of the azobenzene dopants. These results indicate that the host/guest interactions are better when the photoswitchable chiral dopant is more rigid, as is the case with the H-bonded Z state of the hydrazone. The large β values and excellent miscibility of the hydrazone-based dopants in 5CB allowed us to design films that reflect visible structural color. The properties of the azobenzene-based dopants precluded their use in such applications. By codoping 5CB with hydrazone and azobenzene derivatives of opposite chirality, we demonstrated reversible handedness inversion upon photoswitching, providing a versatile soft material platform for reconfigurable photonic materials and colorimetric display technologies.
