Visual β-Sheet-to-β-Turn Transition in Luminescent Polymeric Vesicles for Color-Reporting Drug Delivery.

The secondary structures of polymers significantly influence their properties; however, understanding and modulating polymer conformations remain substantial challenges. Particularly, the β-turn conformation, which is prevalent in proteins, has not been reported in synthetic polymers due to its unclear formation mechanism and extremely poor stability. Additionally, there is a lack of visualization techniques to track conformational and functional transitions in polymers. Here, we designed and synthesized a novel tetraphenylethylene (TPE)-decorated poly(L-cysteine) derivative. Utilizing thioether oxidation as the driving force and strong aromatic-aromatic interactions between TPE molecules as stabilizing mechanism, we reported for the first time a conformational transition from β-sheet to β-turn in polymers. This transition not only significantly enhances fluorescence intensity but also induces chirality and circularly polarized light (CPL) of TPE, providing a new dual-modal approach to real-time monitoring of conformational changes of polymer chains. Furthermore, the conformational transition can trigger specific drug release, with the release process visualized and quantitatively analyzed through fluorescent colors. Such conformation-mediated structural and functional transformations hold significant potential for specific drug delivery and theragnosis of diseases such as cancer.