Adjustable Multicolor Doped Cellulose Nanocrystal Film with Excitation and Temperature Dependence for All-Weather Anticounterfeiting in Sunlight and Darkness

Multicolor tunable persistent room temperature phosphorescence (p-RTP) materials, capable of achieving simultaneous multiple dependent emissions, hold promising commercial prospects in anticounterfeiting encryption applications. However, the anticounterfeiting encryption of these materials can only be achieved in the dark, and there are a few reports of achieving anticounterfeiting encryption effects in both sunlight and darkness. Herein, a flexible strategy for the preparation of highly crystalline, multicolor tunable p-RTP films is provided by mixing water-soluble aromatic sodium salts with a cellulose nanocrystal (CNC)-dispersed aqueous solution and casting the resulting mixture into a film. Specifically, the formation of rigid clusters through hydrogen bonds and ion interactions between sodium aromatic acids and cellulose segments leads to the generation of multiple emission centers, enabling tunable p-RTP emissions ranging from blue to red. This phenomenon can be reasonably explained by a cluster-triggered emission (CTE) mechanism. Moreover, these luminescent materials exhibit excitation (λex-) and temperature (T)-dependent multicolor tunable phosphorescence concurrently. Notably, observing T-dependent full-color gamut persistent phosphorescence under identical excitation conditions has rarely been reported before, which also further supports the CTE mechanism. Variable temperature experiments and theoretical calculations fully demonstrate that responsive emission originates from multiple emission centers formed within the doped film structure. These p-RTP–doped films based on structural color characteristics of CNC have demonstrated exceptional capabilities in information encryption and anticounterfeiting under both sunlight and darkness. This approach combines conventional conjugated units with macromolecular cluster luminescence techniques, providing a sustainable and flexible method for fabricating tunable p-RTP materials while also serving as a reference for intelligent luminescent materials.