Dynamic structural color of amine-modulated photonic crystal films for anti-counterfeiting applications.

Responsive chromic materials with time-dependent color evolution provide a direct and efficient way for visual information expression. However, these systems generally lack simple strategies to control the color evolution process. In this article, time-dependent structural color evolution of the photonic crystal (PC) films has been finely controlled by developing an amine post-modulated strategy. Using the molecule-meditated shear-induced assembly technique (MSAT), large-sized photonic crystal films are fabricated in a fast and scalable manner. Without complex structural design or compositional tuning of the PC films, only change the kinds of introduced amines can easily adjust the hydrophilicity of the matrix of PC films, which can greatly regulate the programmable time-dependent color evolution over time upon water exposure. Mechanistic studies show that the amine modulation convert the carboxyl groups into carboxylates, thereby change the water uptake kinetics, and then vary the color evolution process of the PC film. As a result, the films exhibit continuously tunable color trajectories and provide a new strategy for dynamic information encoding.