Facile access to photo-switchable, dynamic-optical, multi-colored and solid-state materials from carbon dots and cellulose for photo-rewritable paper and advanced anti-counterfeiting

Abstract Dynamic optical materials can respond to external stimuli to give intriguing and chameleon-like visual effect and carry more information, they hence have attracted considerable attention. In this work, we propose a simple and efficient strategy to construct multi-color solid-state carbon dots (CDs) materials with photo-switchable and reversible dynamic-optical properties. A photochromic and positively-charged cellulose derivative C-Im+-SP with an imidazole salt (Im+) group and a spiropyran (SP) group is designed and synthesized. Subsequently, C-Im+-SP is spontaneously coated on the surface of negatively-charged CDs (NCDs) via electrostatic attraction to form a physical protective shell, which not only inhibits aggregation-caused quenching (ACQ) in NCDs but also promotes effective fluorescence resonance energy transfer (FRET). The resultant NCDs@C-Im+-SP exhibits a photo-triggering reversible dynamic-optical property. The NCDs to C-Im+-SP ratio can be used to effectively regulate fluorescence emission and fluorescence kinetics. The polymeric C-Im+-SP shell layer endows NCDs with excellent processability and formability, whereby NCDs@C-Im+-SP materials can be utilized as functional coatings and inks to fabricate photo-rewritable paper and dynamic anti-counterfeit patterns that have considerable potential applications for special coatings, complex anti-counterfeiting, and information encryption.