Self-reporting and refoldable profluorescent single-chain nanoparticles.

We pioneer the formation of self-reporting and refoldable profluorescent single-chain nanoparticles (SCNPs) the light-induced reaction ( = 320 nm) of nitroxide radicals with a photo-active crosslinker. Whereas the tethered nitroxide moiety in these polymers fully quenches the luminescence ( fluorescence) of the aromatic backbone, nitroxide trapping of a transient C-radical leads to the corresponding closed shell alkoxyamine thereby restoring luminescence of the folded SCNP. Hence, the polymer in the folded state is capable of emitting light, while in the non-folded state the luminescence is silenced. Under oxidative conditions the initially folded SCNPs unfold, resulting in luminescence switch-off and the reestablishment of the initial precursor polymer. Critically, we show that the luminescence can be repeatedly silenced and reactivated. Importantly, the self-reporting character of the SCNPs was followed by size-exclusion chromatography (SEC), dynamic light scattering (DLS), fluorescence, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR) and diffusion ordered NMR spectroscopy (DOSY).