Dynamic Information Encryption Technology by Combining Photochromic Spiropyrans and Carbon Dots

Nowadays, high security of information encryption technology, especially time-dependent encryption, is becoming more and more important, but it is still a huge challenge. Here, we have developed a new time-dependent information encryption technology by combining a photochromic spiropyran molecule with a titanium dioxide (TiO2)-grafted carbon dots (CDs) system. The color of these composite materials can be reversibly switched between purple and colorless via irradiation of UV light and white light. Controlling the isomerization of spiropyran units can regulate the mechanism of fluorescence resonance energy transfer (FRET) between the acceptor (spiropyran molecule) and the donor (CDs), thereby resulting in reversible absorption/emission adjustment capability. With the prolongation of irradiation time, the fluorescence emission alters continuously from blue to pink and then to red in 20 min through the FRET process. During this process, false or correct information will be produced and the correct information can be identified at a predesigned period of time. This unique information encryption technology will greatly increase the difficulty of anti-counterfeiting.