Photo-stimulus-responsive dual-emitting fluorescence of spiropyran-encapsulated carbon dots-functionalized silicon dioxide for dynamic information encryption

Developing stimulus-responsive fluorescent materials plays a crucial role in solving emerging requirements for information security. Here, we propose a stimulus-responsive dual-emitting fluorescent material SP@SiO₂-CDs (SP = spiropyran) that was acquired by encapsulating the SP compound in carbon dots (CDs)-functionalized silicon dioxide. This composite shows a blue emission at 470 nm from the CDs and a red emission at approximately 620 nm from SP. With continuous ultraviolet (UV) light irradiation (365 nm), SP molecules undergo the ring-closing to ring-opening process, and significant fluorescence resonance energy transfer can be achieved between SiO₂-CDs and isomeric merocyanine. The SP@SiO₂-CDs powders can show not only photo-chromism from yellow to pink under UV stimulation but also double-emission fluorescence conversion from blue-white to orange-red. When exposed to white light, this dynamic fluorescence behavior can be completely restored to the initial state. Taking full advantage of the time dependence of fluorescence, we have successfully developed a dynamic anticounterfeiting pattern and multiple codes. In addition, by doping with polydimethylsiloxane, we obtained an independent film with high flexibility and mechanical strength and demonstrated its application in time-dependent information encryption. This work provides a novel approach to improve the security of information encryption related to offline portable information encryption.