Anticounterfeiting materials are used to distinguish real banknotes, products, and documents from counterfeits, fakes, or unauthorized replicas. However, conventional anticounterfeiting materials generally exhibit a single anticounterfeiting function, resulting in a low level of security. Herein, a novel anticounterfeiting nanocomposite is demonstrated with numerous prominent security features. The nanocomposite is fabricated by doping upconverting nanoparticles (UCNPs) in a photoresponsive azobenzene‐containing polymer (azopolymer). Because of the cis–trans photoisomerization of the azopolymer, the nanocomposite exhibits photoinduced reversible color changes suitable for anticounterfeiting applications. Additionally, the hard nanocomposite can be converted to a rubber‐like soft solid by light irradiation. Imprinted microstructures are fabricated on the photosoftened nanocomposite, which result in photonic colors. Moreover, polarization‐dependent structures are fabricated on the nanocomposite via photoinduced orientation for encryption. Importantly, UCNPs in the nanocomposite emit visible light upon excitation by near‐infrared light, enabling the observation of various anticounterfeiting structures with high contrast. An advantage of the anticounterfeiting nanocomposite is that the security features can be observed by the naked eye for quick discrimination and can be analyzed using laboratory equipment for higher accuracy. The anticounterfeiting nanocomposite is easily processed on paper, glass, and plastic, which demonstrates its potential anticounterfeiting functions for banknotes, wines, and medicines.

Photoresponsive polymers with multi-azobenzene groups are reviewed and their potential applications in photoactuation, photo-patterning, and photoinduced birefringence are introduced.

Mechanical robustness and healing ability are important properties of polymeric materials. However, the development of mechanically robust yet rapidly healable polymers is challenging. Herein, we demonstrate that long alkyl side chains simultaneously improve mechanical properties and the healing rate of a photoswitchable polymer. The photoswitchable polymer is a polyacrylate. Its side chain contains a hexamethylene spacer, a photoresponsive azobenzene group, and a long n-hexadecyl tail. The n-hexadecyl tail increases the decomposition temperature and glass transition temperature (T g ) of the polymer by 92 and 40 °C, respectively. Such an increase of T g is opposite to textbook knowledge, which makes the polymer robust even at elevated temperatures. The photoswitchable polymer, which has increased T g and improved mechanical properties, is a hard solid under normal usage conditions. It exhibits healing ability because it can be reversibly switched between a solid and a liquid via photoisomerization of the azobenzene groups. The polymer in the liquid state has significantly reduced viscosity for rapid healing. Importantly, the n-hexadecyl tail increases the healing rate of the polymer by 470 times. The introduction of long alkyl side chains is a new strategy for simultaneously improving mechanical properties and the healing rate of polymeric materials.

Photoactuators are promising smart materials that can adapt their shapes upon light illumination. Smart materials with recycling, reusable, and reconfigurable properties are crucial for a sustainable society, and it is important to expand their function. Recently, much effort was made to address the issue of reprocessability and recyclability of photoactuators. Based on the development of polymer chemistry, supramolecular chemistry, and dynamic covalent chemistry, it is now possible to prepare reconfigurable and recyclable photoactuators using azobenzene-containing polymers (azopolymers). Herein, the recent advances on reconfigurable and reprocessable photoactuators, including dynamic crosslinked networks systems and non-covalently crosslinked azobenzene-containing polymers, were reviewed. We discuss the challenges in the field as well as the directions for the development of such photoactuators.