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

Abstract

AbstractWe 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 (CH2)n [n=2,8] chain (Cn), a dipeptide of phe‐phe scaffold, and an unsymmetrical dithienylethene (DTE) moiety (NI‐Cn‐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.