Broadband Circularly Polarized Luminescent Films Based on the Heterogeneous Assembly of Cellulose Nanocrystals

Broadband circularly polarized films display promising applications for multiwavelength lasers and "smart" windows in buildings. Herein, broadband films are fabricated through the heterogeneous assembly of cellulose nanocrystals (CNCs) and thermoplastic polyurethane (TPU) particles in mixed solvents of water and DMF. During the heterogeneous assembly process, a portion of the small TPU particles coassembled with CNCs to form chiral nematic structures and another portion of the TPU particles fused together to form large aggregates. These large aggregates are located around the helical structures of CNCs and induce a twisting effect on the helical axis of the chiral nematic phase. Helical axis twisting continuously occurs in various directions, leading to broad-band reflections of the films. Additionally, multicolor and white right-handed circularly polarized luminescent (CPL) films have been attained by integrating three organic dyes into the chiral structures of CNCs. A high dissymmetry factor value of -0.47 was achieved for the white CPL film.