Thermally Controlled Self-Acid-Releasing Modulated Photo-Switching for Multi-Dimensional Encryption and Anti-Counterfeiting

Abstract

Acid-responsive related materials are diverse and rich in color rendering, playing an important role in the continuous advancement of encryption and anti-counterfeiting technologies. In recent years, although outstanding progress has been achieved in realizing the multi-dimensional information display of the materials to improve the security of acid-responsive related encryption and anti-counterfeiting, commonly used acid vapor or acid solution still has obvious shortcomings in controllability of acid stimulation and the convenience of acquisition in daily life. Herein, a novel strategy of thermally controlled self-acid-releasing is proposed to make acid stimulation available wherever and whenever in practical applications. In contrast to traditional approaches that face cumbersome solution preparation and harsh acid storage, convenient thermal activation can give access to proton acid and control the acidity of the matrix by thermal activation duration. The combination of self-acid-releasing monomer and multi-responsive spiropyran validates the superiority of this strategy while fulfilling high-security anti-counterfeiting. The presence of proton acid in the matrix can enrich the isomerization pathway of spiropyran, achieving a multi-color variation from purple to yellow and ultimately to colorless. Moreover, the differential fading rates induced by the protonation of merocyanine enable the presentation of specific information at designated time nodes, thereby realizing a time-dependent multi-level display. This work will greatly unlock the enormous potential of acids and acid-responsive materials for encryption and anti-counterfeiting.

Keywords: information encryption, anti-counterfeiting, stimulus-responsive, self-acid-releasing, photo-switching