Concurrent Folding and Fluorescent Functionalization of Single-Chain Nanoparticles via Heterogeneous Photochemistry

The controlled folding of synthetic polymers, mimicking the complex behaviors of biomacromolecules, offers the potential to create sophisticated nanostructures with diverse functionalities. Of great significance is the integration of functionalization directly with chain folding, especially through the incorporation of artificial elements not found in nature, which allows unprecedented flexibility in materials design. However, this approach faces significant synthetic challenges, owing to the intricate integration of multiple chemical processes within a single chain. Here, a heterogeneous photochemistry strategy is presented to achieve single-chain polymer folding alongside concurrent fluorescent functionalization, inspired by the stepwise folding mechanism of green fluorescent protein. This method involves pre-folding amphiphilic heterograft random copolymers in water, which facilitates heterogeneous aggregation into distinct domains within single-particle nanostructures, including closely aggregated and molecularly dispersed regions. By employing spatial organization-dependent photochemical reactivity of cyanostilbene moieties, two concurrent processes are enabled: intrachain crosslinking via photodimerization in aggregated domains and fluorescent functionalization via photocyclization to form a green fluorophore in dispersed regions. Additionally, the incorporation of fluorescent dyes via intrachain excitation energy transfer allows for the modulation of emission properties, extending from green to red, and even including white light, making them promising candidates for bioimaging and related applications.