Advances in structural color display of flexible materials and their emerging applications

Photonic crystals (PC) play an increasingly important role in anti-counterfeiting, sensors, displays, and other fields because they produce adjustable structural colors through optical manipulation of photonic stopbands. Flexible structural color materials (FSCMs) eliminate the requirement that traditional structures rely on hard substrates and the problem of poor mechanical quality caused by the stiffness of the building blocks. At the same time, different production technologies and materials provide FSCMs with different abilities to change color in response to stimulation. Therefore, they have attracted extensive attention. This paper summarizes the preparation strategy and variable structural colors of FSCMs. First, a series of preparation strategies for integrating materials with PC are summarized, including the assembly of colloidal spheres on flexible substrates, polymers, direct assembly based on polymers, and 3D printing. Subsequently, the variable structural colors of FSCMs with different stimuli, such as chemical stimuli, temperature, humidity, and mechanical stress, are described in detail. Finally, several potential directions for FSCMs manufacturing and application are introduced, and its prospects and challenges are discussed. It is believed that it will be valuable to promote the use of flexible optical materials.