Optically Ambidextrous Reflection and Luminescence in Self-Organized Left-Handed Chiral Nematic Cellulose Nanocrystal Films

Abstract

Defect-embedded chiral nematic organizations are attractive due to their light manipulation ability that is crucial for photonic applications. Self-assembly of cellulose nanocrystals (CNC) forms a left-handed chiral nematic structure, which makes simultaneous reflection of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light a challenging task. Herein, we present unprecedented evidence that self-organized CNC films with left-handed helical sense and photonic bandgaps (PBG) display ambidextrous CP light reflection with peak reflectivity up to 68% and transform spontaneous photoluminescence to RCP and LCP luminescence with respective |glum| values up to 0.796 and 0.120. These ambidextrous chiroptical properties originate from a left-handed chiral nematic structure consisting of a nematic-like phase, acting as a half-wave retarder, sandwiched between two PBG layers. The latter are spontaneously intercalated into the left-handed helicoids by rapid gelation of CNC colloidal suspensions. We demonstrate that the ambidextrous chiroptical properties can be manipulated by changes in evaporation temperatures, concentrations, and characteristics of CNC suspensions. We showcase the potential of defect-embedded chiral nematic CNC films for the sustainable and scalable development of anti-counterfeiting optical labels.