Photoinduced Energy/Electron Transfer within Single-Chain Nanoparticles.

We demonstrate that single-chain nanoparticles (SCNPs) - compact covalently folded single polymer chains - can increase photocatalytic performance of an embedded catalytic center, compared to the comparable catalytic system in free solution. In particular, we demonstrate that the degree of compaction allows to finely tailor the catalytic activity, thus evidencing that molecular confinement is a key factor in controlling photocatalysis. Specifically, we decorate a linear parent polymer with both photoreactive chalcone moieties as well as Ru(bpy) catalytic centers. We initially construct a SCNP via a photosensitized [2+2] cycloaddition at 510 nm and demonstrate that the SCNP formation is substantially more efficient when the Ru(bpy) units are part of the polymer chain instead of as free molecules in solution. Subsequently, we employ the same Ru(bpy) units as photocatalysts in a model reaction employing pyrene units as charge transfer moieties. We establish that the photocatalytic activity increases as the polymer becomes more compact, reaching peak efficiency, followed by a subsequent decline as the SCNP becomes too compact. Thus, we identify a goldilocks regime of catalyst confinement via SCNP compaction for use in photocatalysis.