Dynamic assembly endows flexible iridescent CNC-based photonic composite film with emergent nonreciprocal chiroptical...

As natural polysaccharide, cellulose nanocrystals (CNCs) provide a sustainable, bio-based nanophotonic platform, and have received considerable attention in recent years. Despite much research, regulating the microstructure of assembled CNC photonic crystals to optimize their versatile chiroptical properties remains challenging. A facile dynamic assembly strategy that can combined with traditional adjusting methods is established to prepare flexible, iridescent CNC-based photonic composite films with a unique Janus surface structure. Because the dynamic assembly of CNC photonic crystals occurs in vortex, this strategy enhances the oriented degree of order, and endows the films with a smooth lower surface and an undulant upper surface, with an interwoven interior composed of inherent left-handed nematic phases and twisted right-handed helical fibers induced by vortex. This unique structure combination results in extraordinary nonreciprocal chiroptical capability based on the opposite faces of the composite films characterized by dual circularly polarized reflection, nonreciprocal circular dichroism (CD), and circularly polarized luminescence (CPL) with asymmetry factors (g_lum) close to 0.1 for the upper surface and - 0.4 for lower surface. This work provides new insights for preparing versatile CNC-based photonic functional materials. Emergent nonreciprocal CPL behavior without chiral enantiomers is of significance for the design and development of next-generation optoelectronic devices.