Erasable invisible ink based on a TPE-based AIE pigment

Developing security inks, which can be permanently erased after reading the information, is of great significance in enhancing the information and data protection of ink anti-counterfeiting applications. Herein, a novel TPE-derived AIE fluorescent molecule (TPE-PA) is synthesized, which produces the strongest fluorescence in THF/water (5:95, v/v, the same below) and EtOH/water (30:70) co-solvents. However, in co-solvents of equal concentration, the fluorescence of TPE-PA pigment in EtOH/water (30:70) was almost entirely quenched with UV light irradiation, whereas in THF/water (5:95), despite the fluorescence showing a decreasing trend, it was not entirely quenched. More intriguingly, TPE-PA pigment self-assembles into fluorescent nanospheres of various particle sizes in co-solvents, and while UV light irradiation quenches the fluorescence of the nanospheres, the particle size of the microspheres marginally reduces. EtOH/water (30:70) was selected as the co-solvent to explore the potential application of the erasable fluorescent anti-counterfeit ink in the field of information storage and encryption. Under ambient and UV light, text written in this ink can be invisible and fluorescent, respectively, but the fluorescence is gradually erased under constant UV light irradiation. The latter can be attributed to the fluorescence quenching caused by the photocyclization and subsequent photo-oxidation of TPE derivatives. This kind of erasable invisible ink, which is dominated by nanospheres, offers a wide range of applications, including privacy protection, data encryption, and anti-counterfeiting.