Spirooxazine-Based Solid-State Photoswitchable Fluorescent Materials for Advanced Time-Resolved Anti-Counterfeiting

Photoswitchable fluorescent materials, with light-tunable and high-contrast fluorescence, are of great interest for anticounterfeiting applications. However, achieving effective photoswitching in the solid state remains a challenge. Here, we report the design of a novel solid-state photoswitchable fluorescent compound, SO-TPE, by covalently linking a spirooxazine (SO) moiety to an aggregation-induced emission molecule, the tetraphenylethene (TPE) moiety. SO-TPE demonstrates reversible absorption and fluorescence modulation in the solid state upon alternating ultraviolet (UV) and visible light irradiation. The distorted TPE moieties provide sufficient free volumes to facilitate efficient photoisomerization between closed-ring and open-ring SO-TPE. Upon UV exposure, SO-TPE exhibits significant color changes from light yellow to blue gray, accompanied by high-contrast fluorescence switching from cyan emission to nonemission. Fluorescence decay spectroscopy and theoretical calculations reveal that the emission of closed-ring SO-TPE originates from the local excited state of the TPE moiety, whereas fluorescence quenching in open-ring SO-TPE results from intramolecular energy transfer from TPE to the SO moiety. Furthermore, combining SO-TPE with Morse code enables time-resolved information encryption, which is highly sought after for applications requiring elevated anticounterfeiting standards. This work presents an ingenious strategy for developing solid-state fluorescent switches based on spirooxazine and paves the way for the design of advanced photoresponsive functional materials for practical applications.