Cycloparaphenylene–Phenalenyl Radical and Its Dimeric Double Nanohoop

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 sp(2)‐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.