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.