Katsuma Matsui, Yasutomo Segawa, Tomotaka Namikawa, Kenji Kamada, and Kenichiro Itami
Chem. Sci. 2012, Advanced Article. DOI:
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The first synthesis of an all-benzene carbon nanocage 1, which represents a junction unit of branched carbon nanotubes, has been achieved. A stepwise assembly of six L-shaped units [cis-di(p-bromophenyl)cyclohexane derivative] and two three-way units (1,3,5-triborylbenzene) by cross-coupling and homocoupling provided the unstrained cyclic precursor. Acid-mediated aromatization of cyclohexane moieties in the precursor resulted in the formation of carbon nanocage 1. Photophysical measurements and DFT studies revealed the unique properties of 1, such as D3 symmetry with degenerate HOMO/HOMO–1 and LUMO/LUMO+1, high fluorescence quantum yield (ΦF = 0.87), and a relatively large two-photon absorption cross section (500 GM at 590 nm), which are attractive for various applications.