Weak-solvent-modulated optical encryption based on perovskite nanocrystals/polymer composites

Smart perovskite-based stimulus-responsive fluorescent materials have attracted considerable attention for confidential information protection, are mostly encapsulated in inorganic mesoporous materials, while little in easily processed polymers. Polymers, despite providing ultra-high resistance to humidity, heat and solvents, inevitably restrict the intrusion of external stimulation sources. In this study, based on perovskite nanocrystals/polymer composites, a weak solvent engineering strategy is rationally designed within the inaugural application in the encryption and decryption of confidential information. N,N-dimethylformamide and water are blended as weak solvents, which can swell and penetrate the polymer after spraying. This triggers the fluorescence quenching effect of the polar solvent on the encapsulated perovskite quantum dots and realizes information encryption. Recrystallization of perovskite can be easily achieved by high-temperature treatment to remove weak solvents, and hence regain its fluorescence properties. By introducing and removing the weak solvent, the perovskite-based composite can be quenched and restored, which enables reversible switching of the fluorescence signal. Surprisingly, the switch is highly effective in encrypting and decrypting various types of information. The optical encryption strategy via weak solvent modification not only provides a new path toward information security transmission but also, with its design friendliness, will contribute to the development and design of myriad innovations for data protection.