Design and synthesize: A new class of photoswitchable materials integrating photochromic properties with aggregation-induced emission behavior via supramolecular self-assembly was developed. The materials (unsymmetrical peptide-bridged naphthalimide–dithienylethene dyads) display fluorescence photoswitching performance in solution, solid, and gel states. One of the developed dithienylethene-based materials was applied in fingerprint detection and in anti-counterfeiting 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 (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.