Visible Light and Temperature Regulated Reflection Colors in Self-supporting Cholesteric Liquid Crystal Physical Gels

Photo-responsive cholesteric liquid crystals (CLCs) have attracted much attention in recent years due to their wide applications in filters, tunable optical lasers, dynamic display devices, etc. However, UV light is usually used as the external stimulus source, which is not environment-friendly enough. On the other hand, the mechanical properties of CLCs are not strong enough for these practical applications. Therefore, it still remains a challenge to endow the CLCs with visible light response and high mechanical properties at the same time. Herein, an axially chiral tetra-fluorinated binaphthyl azobenzene gelator (S-4F-AG) is synthesized. Upon 550 and 450 nm light irradiations, S-4F-AG exhibits excellent photo-switchable behaviors. Notably, the maximum content of cis-isomer and its half-life are as high as 35% and 89 h in acetonitrile, respectively. A self-supporting CLC physical gel with a storage modulus around 104 Pa can be obtained when 3wt% S-4F-AG and 12wt% binaphthyl azobenzene derivative (dopant 2) are co-doped into a nematic LC host P0616A. This CLC physical gel exhibits a temperature-driven blue, green, and red reflection colors reversibly. Importantly, such three primary RGB colors can also be realized by adjusting the exposure time of 550 nm green light. This work lays a solid foundation for the applications ranging from information storage to high-tech anticounterfeit.