Abstract
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.
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.
Yang, Yong