Visible Light Switchable Single-Chain Nanoparticles

We introduce a single-chain nanoparticle (SCNP) system, whose internal structure can be dynamically adjusted by two visible orthogonal colors of light (λ1, max = 620 and λ2, max = 415 nm). We construct linear polymer chains via nitroxide-mediated radical polymerization based on styrene building blocks, decorated with pendent phosphine ligands complexed with catalytically active gold motifs, and collapse the chain with variable amounts of photoresponsive visible light adaptive azobenzene units (13 and 23 mol %), enabling an in-particle cis/trans isomerization. The initial compaction due to the intramolecular cross-linking step is highly dependent on the number of cross-linking points in the initial chain and can reduce the hydrodynamic radius of the chains by up to approximately 44% for the highest azobenzene cross-linker density. The degree of post-folding reversible light-induced compaction is dependent on the number of azo-benzene units in the chain and is associated with a very clearly visible reversible change in UV absorptivity of the SCNP when switching irradiation wavelength. The reversible in-particle cis/trans isomerization is also well observable by 1H NMR spectroscopy, indicating an in-particle light-induced polarity change. It is envisioned that the light-driven dynamically and reversibly altered particle core morphology and structure may find usage to reversibly restrict access into the SCNPs.