A Nonconjugated Radical Polymer with Stable Red Luminescence in Solid State

<p><b>Luminescent organic radicals have attracted much attention due to its distinctive open-shell structure and all-in-one properties on optoelectronics</b><b>, electronics</b><b>, and magnetics</b><b>. However, organic radicals are usually instable</b><b> and only very limited stable structures with π-radicals can </b><b>exhibit luminescent property</b><b> in the isolated state, most of which originate from the family of triphenylmethyl derivatives</b><b>. 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)</b><b>, 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. </b></p>