Hydrogen Bond-Associated Photofluorochromism for Time-Resolved Information Encryption and Anti-counterfeiting.

Time-resolved photofluorochromism constitutes a powerful approach to enhance information encryption security but remains challenging. Herein, we report a strategy of using hydrogen bonds to regulate the time for initiating photofluorochromism. In our strategy, copolymers containing negative photochromic spiropyran (NSP), naphthalimide, and multiple hydrogen-bonding (UPy) units are designed, which display photo-switchable fluorescence resonance energy transfer (FRET) process from naphthalimide donor to the NSP acceptor. Interestingly, the FRET is locked via the dynamic hydrogen-bonding interaction between ring-opened NSP and UPy moieties, resulting in time-dependent fluorescence. The change in fluorescence can be finely regulated via UPy fraction in the polymers. Besides the novel time-dependent fluorescence, the polymers also take advantage of visible-light triggerable, excellent photostability, photoreversibility, and processability. We demonstrate that these properties enable them many application opportunities such as fluorescent security labels and multilevel information encryption patterns.