Rewritable flexible CNC-based composite film with highly homogeneous structural color and time-dependent fluorescence for optical information storage and encryption

The tunable, controllable dual-optical materials combined vivid structural color with conspicuous fluorescence have received widespread interest for coping the rising challenges of information leakage and counterfeiting. Sodium dodecyl sulfate is beneficial to break up the agglomerates and reduce electric potential of cellulose nanocrystals (CNCs), forming a homogeneously iridescent film. Thereby, through facile co-assembly strategy that is notably suitable for large-scale industrial production, we develop a novel, rewritable, flexible CNC composite film with outstanding capability for optical information storage and encryption due to its highly homogeneous structure color and controllable time-dependent fluorescence that can be repeatedly activated/quenched. This film can be directly written on and erased repeatedly without damage, and the written content will spontaneously fade over time. Furthermore, the introduction of superhydrophilic photosensitive ionic liquid enables the prepared film to overcome the deformation induced by inhomogeneous swelling during writing. Under the disguise of dazzling iridescent appearance, the reversible photoinduced dimerization and controllable fluorescence stemmed from coumarin-based molecules allow the encoding of a hidden pattern containing ciphertext on the CNC composite film, offering a promising capability of information storage and encryption. This dual-optical film based on renewable bionanomaterials paves the way for the design and improvement of sustainable functional information materials.