Multicolor SwitchableLatexes Containing a BicyclicAziridine Compound as Anticounterfeiting Inks for Reversible Photopatterning

Abstract

Photochromic latexes are a class of smart materials increasingly valued for their diverse applications such as anticounterfeiting inks and rewritable surfaces. These latexes have the ability to undergo reversible color changes upon exposure to light. An ideal photochromic compound should exhibit rapid switching upon light irradiation. Among different photochromic compounds, 1,3-diazabicyclo[3.1.0]­hex-3-ene (DBH) compounds stand out for their excellent performance in both these aspects, and their photochromic behavior consists of rapid switching between closed-ring and open-ring forms under UV irradiation in both solid and aqueous states. Here, a photochromic compound, DBH-GA, derived from DBH compounds, was synthesized in turn through the reaction of 4-nitroketoaziridine and a natural sugar, galactose (GA), which has not been reported yet. Then, latexes containing different ratios of methyl methacrylate (MMA), acrylamide (AAm), and hydroxyethyl methacrylate (HEMA) monomers were prepared via emulsion copolymerization. Subsequently, DBH-GA was incorporated into latexes for enhanced application and performance by the doping technique to prepare photochromic latexes. The reversible switching of photochromic latexes rapidly occurred from colorless to yellow, blue, or green under UV light (245–400 nm) or upon sunlight exposure for 10 s either in the solid or solution state, demonstrating their multicolor switching ability. These latexes revert to a colorless form when exposed to visible light (578 nm) or in darkness for 6–8 h. Furthermore, all fabricated latexes showed a reversible color change over 10 cycles. The resulting photochromic latexes were applied to papers and fabrics. Our investigation delved into the potential applications of DBH-GA–latexes, including their use as an anticounterfeiting ink for confidential documents with a high level of security, creation of durable photochromic fabrics and papers, development of smart artworks, and rewritable papers. DBH-GA–latexes with fast photoswitchability, environmental compatibility, easy use on different substrates, and dynamic multicolor switching showed great potential as smart materials in various applications.