Peptide Bridged Napthalimide‐Dithienylethene Diad with Aggregation Induced Emission Activity: Application in Forensic Fingerprint Technology

We demonstrate here a simple approach to integrate photochromic property with aggregation-induced emission behavior, via supramolecular self-assembly with the aim to build a new type of photoswitchable materials. We have designed and synthesized two unsymmetrical peptide bridged napthalimide-dithienylethene diad 6 and 7 in a non-conjugated way which shows comparable photo-isomerization speed and rate constant value for cyclization and cycloreversion  accompanied by the noticeable naked-eye color change from pale yellow to purple.  Both the compounds 6 and 7 show considerably high fatigue resistance for at least 45 cycles without loss of sensitivity and compound 7 exhibits fluorescence photoswitching performance in solution, solid state, as well as in gel form through FRET mechanism. Interestingly, compound 7 self-assembled in THF/water (30:70) media to exhibit aggregation induced emission behavior and showed an organogelation property in ethanol with minimum gelation concentration (6 mg/mL). Taking advantage of high fluorescence photoswitching performance in solution as well as in solid state along with AIE, the developed DTE based material was applied in latent fingerprints and in anti-counterfeiting technology in non-invasive manner. To the best of our knowledge, this is the 1st example of peptide bridged NI-DTE material which can be used in forensic sciences as fingerprint detecting agent.