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The first example of a neutral spin‐delocalized carbon‐nanoring radical was achieved by integration of the open‐shell phenalenyl unit into cycloparaphenylene (CPP). Spin distribution in this hydrocarbon is localized primarily on the phenalenyl segment and partially on the CPP segment as a consequence of steric and electronic effects. The resulting geometry is reminiscent of a diamond ring, with pseudo‐perpendicular arrangement of the radial and the planar π‐surface. The phenylene rings attached directly to the phenalenyl unit give rise to a steric effect that governs a highly selective dimerization pathway, yielding a giant double nanohoop. Its π‐framework made of 158 sp2‐carbon atoms was elucidated by single‐crystal X‐ray diffraction, which revealed a three‐segment CPP‐peropyrene‐CPP structure. This nanocarbon shows a fluorescence profile characteristic of peropyrene, regardless of which segment gets excited. These results in conjunction with DFT suggest that adjusting the size of the CPP segments in this double nanohoop could deliver donor–acceptor systems., A neutral open‐shell carbon nanoring was achieved by integration of the phenalenyl unit into the cycloparaphenylene framework. It is shown that the spin distribution and reactivity of this hydrocarbon in the shape of a diamond ring are a result of steric and electronic effects and that selective dimerization yields a double nanohoop with a radial‐planar‐radial arrangement of its three π‐conjugated segments comprising a total of 158 sp2‐carbon atoms.

We demonstrate that structurally complex carbon nanostructures can be achieved via a synthetic approach that capitalizes on a π-radical reaction cascade. The cascade is triggered by oxidation of a dihydro precursor of helical diradicaloid nonacethrene to give a chiral contorted polycyclic aromatic hydrocarbon named hypercethrene. In this ten-electron oxidation process, four σ-bonds, one π-bond, and three six-membered rings are formed in a sequence of up to nine steps to yield a 72-carbon-atom warped framework, comprising two configurationally locked [7]helicene units, a fluorescent peropyrene unit, and two precisely installed sp; 3; -defects. The key intermediate in this cascade is a closed nonacethrene derivative with one quaternary sp; 3; -center, presumably formed via an electrocyclic ring closure of nonacethrene, which, when activated by oxidation, undergoes a reaction cascade analogous to the oxidative dimerization of phenalenyl to peropyrene. By controlling the amount of oxidant used, two intermediates and one side product could be isolated and fully characterized, including single-crystal X-ray diffraction analysis, and two intermediates were detected by electron paramagnetic resonance spectroscopy. In concert with density functional theory calculations, these intermediates support the proposed reaction mechanism. Compared to peropyrene, the absorption and emission of hypercethrene are slightly red-shifted on account of extended π-conjugation and the fluorescence quantum yield of 0.45 is decreased by a factor of ∼2. Enantiomerically enriched hypercethrene displays circularly polarized luminescence with a brightness value of 8.3 M; -1; cm; -1; . Our results show that reactions of graphene-based π-radicals-typically considered an "undefined decomposition" of non-zero-spin materials-can be well-defined and selective, and have potential to be transformed into a step-economic synthetic method toward complex carbon nanostructures.

Molecules that contain one or more unpaired electrons delocalized within a ?-conjugated backbone are promising candidates for applications in spin electronics or simply 'spintronics'. Our group develops functional organic materials based on ?-conjugated hydrocarbon molecules, where the electrons are unpaired either in the ground state or in the excited state that is low in energy and can be populated thermally. We aim to learn how to introduce and control a multitude of properties, namely, optical, chiroptical, magnetic, and conductive, in a bulk material made of these molecules, by manipulating spin interactions between the unpaired electrons. The first model system that was developed in our group is a hydrocarbon named cethrene, which has a diradicaloid singlet ground state and a low-lying triplet excited state. In this article, the structural parameters and their impact on the properties and reactivity of cethrene are discussed within the realm of the three C's that symbolize cethrene's C-shape, chirality, and chameleonic reactivity.