Near-White Circularly Polarized Luminescence by Color Mixing Utilizing Surface-Fluorophore-Modified Cellulose...

Herein, we present the fabrication of freestanding cellulose nanocrystal (CNC) films exhibiting blue, green, red, and, in combination, near-white right-handed CPL (RCPL) through covalent grafting of achiral fluorophores to CNCs via Steglich esterification. The weakly-twisted CNCs, hierarchically organized through evaporation-induced self-assembly, act as chiral scaffolds enforcing the supramolecular chirality. The ensuing composite CNC films display dye-specific photoluminescence with maximum negative luminescence dissymmetry ( $g_{lum}$ ) values of -0.15, -0.16, and -0.11 for blue, green, and red emissive films, respectively, indicative of preferential right-handed emission. Morphological evaluation via scanning electron microscopy (SEM) reveals well-defined Bouligand arches, and studies by polarized optical microscopy (POM) fingerprint textures, each confirming the preservation of chiral nematic ordering across all emissive films. Notably, by integration of all three fluorescent dyes within the CNC matrix, near-white CPL was achieved by color mixing, as corroborated by CIE 1931 chromaticity analysis with $|g_{lum}|$ values ranging from 0.05 to 0.10 over the visible spectral region, with $\sim$ 90% permanence of the fluorescence over a 12-h irradiation period. This approach establishes the basic framework for generating mechanically and thermally robust CPL-active, principally bio-renewable chiral CNC materials and optical elements for advanced displays, optoelectronic devices, and chiroptical sensing platforms.