Photonic Bioderived Materials with Discrete Helical Organization

Local and global chirality control is essential for many prospective technologies, including lightweight tough materials, photonics, optical sensors, pharmaceutics, and electronics [1]. Natural polymers, such as polysaccharides and plant-derived nanocelluloses in particular, self-organize into hierarchical structures, enabling mechanical robustness, bright iridescent color and emission, and polarized light reflection. This set of biomimetic functionalities is engendered by individual components such as high-aspect ratio cellulose nanocrystals (CNCs) that naturally assemble into a left-handed helical pitch [2].
Here, we discuss how optically active films with pre-programmed handedness (left or right) can be constructed via layer-by-layer shear-induced 3D printing with clockwise and counter-clockwise twisted printing vectors [3]. The resulting thin films are transparent yet exhibit pre-determined mirror symmetrical optical activity dominated by linear and circular birefringence, enabling distinction of absorbed and emitted circularly polarized light (CPL) with different handedness. The resulting films possess complex light polarization behavior due to step-like changes in linear birefringence within each deposited layer and give rise to pre-programmed circular birefringence, not seen in conventional self-assembled films. Furthermore, intercalating an organic dye into the printed structures induces circularly polarized luminescence while preserving high transmittance and handedness. Furthermore, twisted CNC films with dual CPL and near-infra-red range (NIR) reflectance properties are demonstrated [4]. It is demonstrated that by manipulation of the process parameters of the discrete twisted helical organization– twisting angle and anisotropic block thickness – distinct CD patterns and transmittance could be achieved. We further show that the produced films could be treated as optical twisted metamaterials swinging between two extremes – a 1D photonic crystal aka Bragg stacks from anisotropic blocks and a conventional continuous chiral nematic phases. These twisted chiroptical metamaterials with tunable circular polarization, reflection, absorption, and emission can be explored for optical filters, photonic coatings, chiral sensors, and optical encryption as well for achieving tailored photonic bio-skin and exoskeletons for visual camouflaging.

1 D. Nepal, et al. Hierarchically Structured Bioinspired Nanocomposites, Nature Mat., 2023, 22, 18.
2 R. Xiong, et al. Natural Biopolymers for Organized Photonic Structures, Chem. Soc. Review, 2020, 49, 983.
3 D. Bukharina, et al.^, Left and Right-Handed Light Reflection and Emission in Ultrathin Films with Printed Helicity, Adv. Funct. Mater., 2024, in print, 10.1002/adfm.202404857
4. B. Dimitrov, et al. Discrete Twisted Films From Cellulose Nanocrystals with Dual Near-Infra-Red Bandgaps and Chiroptical Properties, Adv. Optical Mater., 2024, submitted