Unidirectional cellulose nanocrystal hydrogel for bio-based invertible chiral optics and sensors

Realizing invertible chiral optical properties in the visible region is crucial for developing optical systems with applications in displays and sensors. Achieving this with cellulose nanocrystal (CNC)-based materials is difficult because their chiral nematic structures are inherently fixed in a left-handed configuration. Here, we demonstrate that by introducing a unidirectional (or monodomain nematic-like) CNC hydrogel as a retardation layer onto a chiral nematic CNC film, the naturally left-handed chiral reflections of CNC films can be converted to right-handed reflections. Furthermore, the right-handed reflection can be switched back to their left-handed state simply by applying pressure. These mechano-responsive invertible chiral optical phenomena, along with the manipulation of light through the cooperation of unidirectional and chiral nematic CNC structures, opens up new opportunities for developing bio-based invertible chiral optics and sensors.