Turn-on type stimuli-responsive fluorescence of diaminomaleonitrile derivatives: Implication for information encryption-decryption

We report the synthesis and photoluminescence of a new molecular system designed based on diaminomaleonitrile derivatives. They are endowed with both aggregation-induced emission (AIE) and intramolecular charge transfer (ICT) natures. More importantly, one of them, ie., 2-amino-3-((E)-(4-(diethylamino) benzylidene) amino)maleonitrile (C4), exhibits unique vapochromism, namely a turn-on fluorescence in response to organic vapour. Based on spectral analysis, DFT calculation, SEM observation and crystallographic data, a mechanism for the vapochromic fluorescence was proposed: Donor-acceptor (D-A) coupling, which caused by the combined effect of pi-pi interaction and electrostatic force, is mainly responsible for the initial weak fluorescence of C4; Its fluorescence will be spontaneously restored when D-A coupling is destructed by organic vapour. Such vapochromism of C4 motivated us to develop a new optical data storage (ODS) capable of data encryption-decryption. Encrypted information in binary form can be stored on the device fabricated by C4 film, which cannot be read unless it is treated by solvent fumigaition. After this decryption process, the fluorescent signals are remarkably enhanced, showing 3 similar to 6-fold higher than false signals, which makes the former easy to be identified by both naked eyes and instruments. This study presents a successful archetype of security data storage, which only displays data at a specific condition. Otherwise, the data are concealed to avoid illegal reading or copying.