Long-Afterglow Materials Enabled by the Confinement Effect of Cellulose Nanocrystals Cholesteric Liquid Crystals

Room-temperature phosphorescence (RTP) is highly sought after for optical sensing and encryption, but is constrained by triplet exciton quenching. This challenge is addressed by employing cellulose nanocrystals (CNC), specifically carboxylated CNC, as a cholesteric host and coronene tetracarboxylate (CS) as a phosphorescent guest. The self-assembled CNC matrix provides a rigid, anisotropic microenvironment through nanorod ordering and hydrogen bonding with CS, effectively suppressing non-radiative relaxation. Systematic CS loading (0.3-5 wt%) reveals optimal performance at 1 wt% (lifetime: 1.756 s, quantum yield: 9.4%, 8 s afterglow), while higher loadings disrupt ordering and induce aggregation quenching. Three application strategies are further demonstrated: doping-contrast Morse coding, water/thermal rewritable patterns, and Rhodamine B-mediated multicolor time-sequenced luminescence. Collectively, these results show that CNC cholesteric order actively enhances RTP, establishing these biocomposite films as viable materials for advanced anti-counterfeiting and encryption systems.