We report a series of tunable and persistent [4]-helicene neutral radicals by chemical reduction of the [4]-helicenium cation analogue. EPR spectroscopy and DFT calculations indicate that the unpaired electron is localized at the central carbon atom.

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Symmetrical non-aqueous organic redox flow batteries are highly promising systems for electrochemical energy storage. A higher solubility and energy density of a previously described robust ROM was obtained by straightforward nitration of its core.

In recent years, in-situ generated organic radicals have been used as highly potent photoinduced electron transfer (PET) agents resulting in catalytic systems as reducing as alkaline metals that can activate remarkably stable bonds. However, the transient nature of these doublet state open-shell species has led to debatable mechanistic studies, hindering adoption and development. Herein, we document the use of an isolated and stable neutral organic radical as a highly photoreducing species with a reduction potential lower than – 3.5 V vs SCE. The isolated radical offers a unique platform to investigate the mechanism behind the photocatalytic activity of organic radicals. Our mechanistic study supports the involvement of solvated electrons formed by single electron transfer (SET) between the short-lived excited state organic radical and the solvent.

<p>Stable organic radicals have gained considerable attention in the fields of catalysis and material sciences. In particular, helical molecules are of great interest in the development and application of novel organic radicals in optoelectronic and spintronic materials. Here we report the syntheses of highly stable neutral quinolinoacridine radicals by chemical reduction of their quinolinoacridinium cation analogs. The crystal structures of these [4]helicene radicals were determined by X-ray diffraction. Electron paramagnetic resonance (EPR) measurements, supported by density functional theory (DFT) calculations, indicate that the unpaired electron is mostly localized, showing more than 40% of spin density located at the central carbon of the [4]helicene radicals. Quantitative conversion from neutral radical to cation is observed upon exposure to air, monitored via UV-vis spectroscopy. The successful photoreductive dehalogenation of aryl halides occurs in the presence of 10 mol% of [4]helicene radical under blue light.<b></b></p>