Dynamic Fluorescent Anti-Counterfeiting Labels Based on Conjugated Polymers Confined in Submicron Fibrous Membranes

Novel core-shell materials SiO2@Tb-MOF for the incorporation of spiropyran molecules and its application in dynamic advanced information encryption

Dynamic fluorescent switches with multiple light outputs offer promising opportunities for advanced security encryption. However, the achievement of dynamic emission, particularly when based on the timing of external stimuli, continues to present a significant challenge. Herein, a unique dynamic fluorescent switch was developed by integrating spiropyran molecules (SP) into a core-shell structure (SiO2@Tb-MOF). The core-shell structure, derived from lanthanide complexes and silica microspheres, was synthesized under solvothermal conditions. This structure not only preserves the green fluorescence emission of Tb-MOF, but also results in a substantial specific surface area and mesoporous pore size from SiO2, which is advantageous for incorporating SP molecules to create a dynamic fluorescent switch, SP ⊂ SiO2@Tb-MOF. Upon exposure to ultraviolet light, SP gradually transitions into the merocyanine form (MC), displaying a pronounced absorption band at approximately 550 nm. Concurrently, a fluorescence resonance energy transfer (FRET) process is initiated between Tb3+ and the merocyanine isomers. With prolonged exposure to UV light, the fluorescence color shifts progressively from green to red, facilitated by the ongoing FRET process. Moreover, SP ⊂ SiO2@Tb-MOF is doped with polydimethylsiloxane to fabricate a film. Utilizing time-dependent fluorescence, dynamic encryption patterns and advanced information encryption were investigated. This work provides a design basis for how to better construct core-shell structures and combine them with SP molecules to prepare dynamic fluorescent materials, and paves a way for constructing advanced encryption materials with higher safety requirements.

Fluorescent Materials Based on Spiropyran for Advanced Anti-Counterfeiting and Information Encryption

In daily life, counterfeit and substandard products, particularly currency, medicine, food, and confidential documents, are capable of bringing about very serious consequences. The development of anti-counterfeiting and authentication technologies with multilevel securities is a powerful means to overcome this challenge. Among various anti-counterfeiting technologies, fluorescent anti-counterfeiting technology is well-known and commonly used to fight counterfeiters due to its wide material source, low cost, simple usage, good concealment, and simple response mechanism. Spiropyran is favored by scientists in the fields of anti-counterfeiting and information encryption due to its reversible photochromic property. Here, we summarize the current available spiropyran-based fluorescent materials from design to anti-counterfeiting applications. This review will be help scientists to design and develop fluorescent anti-counterfeiting materials with high security, high performance, quick response, and high anti-counterfeiting level.

Preparation and dynamic color-changing study of fluorescent polymer nanoparticles for individualized and customized anti-counterfeiting application

Preparing new fluorescent materials for individualized and customized anti-counterfeiting applications to meet needs from the rapid development of e-commerce is of great significance. This paper reports the preparation of dynamic color-changing fluorescent polymer nanoparticles (PNPs) by constructing a fluorescence resonance energy transfer (FRET) pair between aggregation-induced emission (AIE) structures and photochromic structures. At first, methyl methacrylate (MMA) was used as the main monomer and tetraphenylethylene (TPE, a typical AIE structure) modified methacrylate (TPE-MA) and photochromic spiropyran (SP) modified methacrylate (SP-MA) as minor monomers were copolymerized to obtain the ternary copolymer PMMA-TPE-SP. Then, two types of PNPs based on this terpolymer was prepared via the reprecipitation method, with and without the addition of an amphiphilic polymer as the surfactant. The photophysical study shows that the fluorescence color of PNPs dynamically changes from blue to light violet and finally to red under UV light irradiation, a process that can be reversed under visible light. The PNPs were alternately irradiated with UV light and visible light for 10 cycles, which proved their good photoswitching reproducibility. The PNPs prepared with addition of surfactant were found to have stronger fluorescence and better stability. Finally, the photochromic fluorescent inks were prepared based on these PNPs. Several anti-counterfeiting scenarios and modes were designed, exhibiting excellent photochromic behavior on cellulose paper, even after 120 days of long-term storage. With simple equipment, desirable anti-counterfeiting effects with dynamic fluorescence color changing was achieved. This study demonstrated a promising hard-to-imitate anti-counterfeiting encryption strategy, which can achieve multiple outputs with simple operation and can be personalized and customized as needed.

Green syntheses of silk fibroin/wool keratin-protected AuAg nanoclusters with enhanced fluorescence for multicolor and patterned anti-counterfeiting

Counterfeiting is a serious worldwide issue that threatens human health and economic security. How to apply anti-counterfeiting techniques to textile materials remains a great challenge. Herein, we report bimetallic AuAg nanoclusters (NCs) synthesized by one-step reduction of chloroauric acid (HAuCl4) and silver nitrate (AgNO3) with wool keratin (WK) as reducer and silk fibroin (SF) as stabilizer. The strongest orange-red fluorescence under ultraviolet light as well as the highest zeta potential absolute values of -27.97 mV were simultaneously realized in the optimal proportion Au-AgNCs2 (WK/SF is 3/2), which was further processed to a series of anti-counterfeiting films by blending with SF, silk sericin (SS), and polyvinyl alcohol (PVA). After successfully being numbered into fifteen colors, a dark blue-orange-dark red-dark blue cyclic fluorescent anti-counterfeiting color chart was designed. In addition, a two-Maxwell-unit model was constructed to assist with the microstructure analysis, which found that the formation of hydrogen bonds and the secondary structure transition from α-helices to β-sheets during stretching were responsible for improving the mechanical properties and the two-staged fracture curves of films, respectively. Finally, a patterned and multicolor fluorescence anti-counterfeiting fabric application was demonstrated by combining the color chart and screen printing, indicating the great potential in textile anti-counterfeiting.