Responsive Chiral Photonic Cellulose Nanocrystal Materials

Abstract

Responsive photonic crystals have attracted significant attention in fundamental scientific research and technological applications. Upon applying external stimuli, such as mechanical, electrical, magnetic, and optical triggers, the optical properties of photonic crystals can be actively tuned. Among a large number of photonic crystals, cellulose nanocrystals (CNCs) are considered one of the most promising materials due to their renewability, simplicity of preparation, and unprecedented chirality. A comprehensive overview of the fundamental design principles, methodologies, responsive mechanisms, and practical applications of responsive chiral photonic CNC materials is presented here. The changes in helix pitch, refractive index, orientation, and resulting structural and optical properties of chiral photonic CNCs in response to various stimuli are discussed. Thereafter, novel applications of responsive chiral photonic CNCs, such as colorimetric sensors, photonic actuators, rewritable photonic papers, and anti‐counterfeiting smart tags are described. We conclude by discussing future challenges and opportunities for developing high‐performance responsive chiral photonic CNC materials.

From 0 toN: circularly polarized luminescence generation from achiral luminophores in fibrous morphologies

“…(i) At the nanoscale, the chiral motifs and achiral luminophores self-assemble into a 1D fibrous architecture (e.g., nanohelixes, nanotwists, and nanotubes), where the chirality could be transferred from chiral molecules to a supramolecular system. [28][29][30] (ii) At the microscale, nano-fibrous building blocks (e.g., liquid crystals, 31 cellulose nanocrystals, [32][33][34] and twisted crystallites [35][36][37] ) are capable of organizing into a chiral solid film, showing the selective reflection activity to transform the emission of achiral luminophores into CPL with well-defined handedness. (iii) At the macroscale, continuous macroscopic fibers could impart CPL properties to the incorporated achiral luminophores via external twisting, 38 and their traditional spinning methodology and twisting process make scalable production of CPL materials realistic.…”

Optical Properties of Slot‐Die Coated Hybrid Colloid/Cellulose‐Nanofibril Thin Films

“…[12][13][14] Often, cellulose nanocrystals (CNC) are used for structural colors, for example, in dried films forming nematic hierarchical nanostructures. [15] Due to the evaporationinduced self-assembly, ordered structures occur, which are responsible for the structural colors. [16] When using cellulose nanocrystals' arrangements, one determining parameter of the structural color is the helical stacking [17] with a blue-shift of the reflected intensity due to a changing pitch and the expulsion of water during drying increasing the refractive index contrast.…”

Mechanically Responsive Circularly Polarized Luminescence from Cellulose‐Nanocrystal‐Based Shape‐Memory Polymers

“…When the helical pitch is on the order of the wavelength of visible light, films of CNCs can display vivid iridescence. [24,25] Many recent studies have demonstrated the potential use of iridescent CNC films for sensing, [26][27][28] encoding, [29][30][31] pigments, [32] and optical devices. [33,34] An interesting physical consequence of the helical structure is that the CNC films selectively reflect left-handed circularly polarized light and transmit right-handed circularly polarized light [35][36][37] These properties make CNC films excellent chiral hosts to achieve CPL.…”

“…When the helical pitch is on the order of the wavelength of visible light, films of CNCs can display vivid iridescence. [ 24,25 ] Many recent studies have demonstrated the potential use of iridescent CNC films for sensing, [ 26–28 ] encoding, [ 29–31 ] pigments, [ 32 ] and optical devices. [ 33,34 ]…”