Luminescent organic radicals are an exotic class of molecules on account of their spin nature and notoriously difficult synthesis. We report on the synthesis of a neutral π-radical composed of phenalenyl combined with a semiquinone substructure, 9-hydroxy-naphthoxanthenyl (NXOH), which is fluorescent and paramagnetic at room temperature. NXOH can be readily obtained by reduction of its non-fluorescent cationic precursor NXOH+ using either chemical or electrochemical means under mild conditions. In an electrolyte solution, NXOH reversibly oxidizes back to NXOH+ in the presence of O2 or applying a suitable electric potential with quantitative yield. The reversible redox behavior, which allows for a switching of fluorescence as well as magnetic signal upon electron transfer process, highlights the promise of phenalenyl radicals for bio-imaging or spintronics applications.

Photoluminescent phenalenyl-type radical

253rd National Meeting (2017)

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