Breaking Acid‐Induced Fluorescence Quenching in Fluorescein Derivatives: Surfactant‐Directed Aggregation Control for On‐Demand Multiple Encryption

Abstract The inactivation of fluorescein derivatives due to proton attack under acidic conditions completely limits the optical properties and hinders a wide range of applications. Aggregation‐related quenching is found to be another fundamental trait in addition to spirocyclization. Self‐assembled dispersions of surfactants have been shown to precisely break the quenching limitation, thereby fully restoring or even enhancing the original optical properties. By combining experimental characterizations and theoretical calculations, the mechanism by which surfactants enable programmable fluorescence recovery is through proton sequestration and colloidal redispersion mediated by host‐guest complexation and hydrogen bond reconstruction. Such a strategy achieves ≈2150‐fold increase in fluorescence intensity at pH 1.0. Herein, a novel encryption strategy is presented utilizing the surfactant‐activated optical performance of fluorescein derivatives, wherein proton‐induced molecular aggregation triggers simultaneous chromogenic quenching and fluorescence suppression. The coupled inkjet printing technology is responsible for loading the dye onto the Whatman fiber paper, and the subsequent triggering of the release is achieved by spraying the surfactant solution. This innovation has led to the development of a fast response (1 s), low‐priced, user‐friendly, multi‐channel encryption system. The anti‐counterfeiting system has multiple optical switching characteristics, showing broad applications in the fields of anti‐counterfeiting, information encryption, and intelligent packaging.