Peptide‐Bridged Naphthalimide–Dithienylethene Dyad with Aggregation‐Induced‐Emission Activity: Application in Forensic Fingerprint Technology

Abstract We demonstrate here a simple approach to integrate photochromic properties 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 naphthalimide–dithienylethene dyads, each composed of naphthalimide (NI), an alkyl (CH 2 ) n [ n =2,8] chain (C n ), a dipeptide of phe‐phe scaffold, and an unsymmetrical dithienylethene (DTE) moiety (NI‐C n ‐pep‐DTE; 6 : n =2; 7 : n =8). Dyads 6 and 7 show comparable photo‐isomerization speed and rate constant (K) values for cyclization (75 s, K=0.049 s −1 for 6 , 65 s, K=0.056 s −1 for 7 ) and cycloreversion (105 s, K=0.037 s −1 for 6 , 100 s, K=0.023 s −1 for 7 ) accompanied by a noticeable naked‐eye color change from pale yellow ( 6 o / 7 o ; open forms) to purple ( 6 c / 7 c ; closed forms). Both compounds 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 a FRET mechanism. The developed dithienylethene (DTE)‐based material was applied in latent fingerprints (LFPs) and in anti‐counterfeiting technology in a non‐invasive manner.