A Nonconjugated Radical Polymer with Stable Red Luminescence in Solid State

Luminescent organic radicals have attracted much attention due to its distinctive open-shell structure and all-in-one properties on optoelectronics, electronics, and magnetics. However, organic radicals are usually instable and only very limited stable structures with π-radicals can exhibit luminescent property in the isolated state, most of which originate from the family of triphenylmethyl derivatives. Here, we report an unusual radical luminescence phenomenon that nonconjugated radical polymer can readily emits red luminescence at ~635 nm in the solid state. A traditional luminescence quencher, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), was turned into a red chromophore when grafted onto a polymer backbone. Experimental data confirms the emission is associated with the nitroxide radicals and is also affected by the packing of polymer. As a proof of concept, a biomedical application in intracellular ascorbic acid visualization is demonstrated. This work discloses a novel class of luminescent radicals and provides a distinctive and simple pathway for stable radical luminescence.