Position Matters: Fluorescent Positional Isomers for Reliable Multichannel Encryption Devices

Fluorescence signals have been widely used in information encryption for a few decades, but still suffer from limited reliability. Here, reversible multichannel fluorescent devices with encrypted information were constructed, based on two fluorescent positional isomers of a diphenylquinoxaline derivative. Possessing the same core fluorescent group and acid‐/pH‐responsive mechanism, the two isomers showed different fluorescence colors in an acidic environment; this allowed us to realize stepwise encryption of information in orthogonal fluorescence channels. Because the protonation was reversible, the revealed information could be re‐encrypted simply by heating. This approach highlights the value of positional isomers to build multichannel encryption devices, improving their reliability on the molecular level.