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 (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.

Recent progress on the construction and application of dithienylethene‐based photochromic AIEgens

“…Naphthalimide (NI), is widely used as an adjustable fluorescent core, which can tune not only the intriguing supramolecular systems through π‐system but also can alter the photophysical behavior in aggregated state 48 . Thakur and coworkers 49 reported two peptide‐bridged NI‐DTE Dyad (NI‐PT‐DTE‐1, NI‐PT‐DTE‐2) (Figure 15). In this system, unsymmetrical DTE unit and fluorescent chromophore (NI) are covalently connected by a dipeptide unit linked via variable (2,8)‐alkyl chain length.…”

“…Fingerprint imaging technology of NI‐PT‐DTE‐2 was examined by Thakur and coworkers 49 . At first, when bare fingers were pressed on a glass petri dish, no patterns were displayed after UV/visible‐light irradiation.…”

Ferrocene–Dithienylethene–Naphthalenediimide-Based Multifunctional Molecular Switch: Applications in Anticounterfeiting and Controlled Singlet Oxygen Generation

“…14 Reversible redox between the ferrocene and ferrocenium states give us the edge to establish a PET-based modulation for the tuning of the optical properties, especially the emission profile of a suitable fluorophore. 15 Apart from that, incorporation of ferrocene can also give us the opportunity to get different ionization potential (IP) values in the two isomeric forms of DTE, leading to its utility in optoelectronics. 16 Thus, for effective utilization of both FRET-and PET-based switching, the choice of the fluorophore becomes very crucial, where the fluorophore needs to be optically viable for the energy-transfer process as well as electronically deficient species for efficient acceptance of excited electrons.…”

“…With excellent redox properties, ability to tune the optical properties of any fluorophore by PET, high crystalline nature, and good solubility in organic solvents, ferrocene stands out to be the candidate with the most potential in constructing multiresponsive switches . Reversible redox between the ferrocene and ferrocenium states give us the edge to establish a PET-based modulation for the tuning of the optical properties, especially the emission profile of a suitable fluorophore . Apart from that, incorporation of ferrocene can also give us the opportunity to get different ionization potential (IP) values in the two isomeric forms of DTE, leading to its utility in optoelectronics .…”