Stable organic radicals have been of great academic interest not only in the context of fundamental understanding of reactive intermediates but also because of their numerous applications as functional materials. Apart from the early examples of triphenylmethyl and TEMPO derivatives, reports on air- and water-stable organic radicals are scarce, and their development remains a challenge. Herein, we present the design and synthesis of a novel organic radical based on a 1,2-dicarbonyl scaffold supported by N-heterocyclic carbenes (NHCs). The presented radical cations exhibit remarkable stability toward various harsh conditions, such as the presence of reactive chemicals (reductants, oxidants, strong acids, and bases) or high temperatures, by far exceeding the stability of triphenylmethyl and TEMPO radicals. In addition, physiological conditions including aqueous buffer and blood serum are tolerated. The steric and electronic stabilization provided by the two NHC moieties enabled the successful design of the highly stable radical.

<div>The present manuscript describes the design, synthesis, and characterization of the most stable organic radical reported up to date.</div><div><br></div><div>Here we report:</div><div>▪ Synthesis and full characterization including X-ray structure of stable 1,2-dicarbonyl radicals</div><div>▪ Proposed mechanism for the formation of the presented radicals</div><div>▪ Redox reactivity of the radicals</div><div>▪ Stability of the radicals under various organic and inorganic conditions</div><div><u></u></div>

<div>The present manuscript describes the design, synthesis, and characterization of the most stable organic radical reported up to date.</div><div><br></div><div>Here we report:</div><div>▪ Synthesis and full characterization including X-ray structure of stable 1,2-dicarbonyl radicals</div><div>▪ Proposed mechanism for the formation of the presented radicals</div><div>▪ Redox reactivity of the radicals</div><div>▪ Stability of the radicals under various organic and inorganic conditions</div><div>▪ Demonstration of the radicals as potential organic radical contrast agent candidate</div><div><u></u></div>

<div>The present manuscript describes the design, synthesis, and characterization of the most stable organic radical reported up to date.</div><div><br></div><div>Here we report:</div><div>▪ Synthesis and full characterization including X-ray structure of stable 1,2-dicarbonyl radicals</div><div>▪ Proposed mechanism for the formation of the presented radicals</div><div>▪ Redox reactivity of the radicals</div><div>▪ Stability of the radicals under various organic and inorganic conditions</div><div>▪ Demonstration of the radicals as potential organic radical contrast agent candidate</div><div><u></u></div>