Synthesis and properties of all-benzene carbon nanocages: a junction unit of branched carbon nanotubes

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 D-3 symmetry with degenerate HOMO/HOMO - 1 and LUMO/LUMO + 1, high fluorescence quantum yield (Phi(F) = 0.87), and a relatively large two-photon absorption cross section (500 GM at 590 nm), which are attractive for various applications.