Multiple anti-counterfeiting guarantees from simple spiropyran derivatives with solid photochromism and mechanochromism

Stimuli-responsive materials have gained a lot of attention recently because of their promising use in data storage, drug release, sensing, and anti-counterfeiting. Herein, we report spiropyran-silane derivatives with dual reversible characteristics as photo- and mechanochromic materials. These molecules are susceptible to ultraviolet (UV) light and exhibit efficient and reversible solid-state photoswitching under alternating UV light and heat/visible light treatment for at least 100 cycles. Meanwhile, they can change colors under slight grinding. Additionally, they have the following advantages as anti-counterfeiting materials: (1) they show high contrast and reversibility to design complex anti-counterfeit patterns; (2) the response and recovery is fast, and the validations can be realized in a short time; (3) they can achieve multiple stimuli responses of both fluorescence and color changes controlled by either UV light or mechanical force. In particular, based on mechanochromism, handwriting can be used as another guarantee to strengthen anti-counterfeiting. The multiple guarantees will greatly improve the reliability of anti-counterfeiting measures, making counterfeiting more difficult.