Synthesis and Size-Dependent Properties of [12], [16], and [24]Carbon Nanobelts

The
synthesis and X-ray crystal structure of the first member of
the carbon nanobelt family is reported. [12]Carbon nanobelt ([12]­CNB)
was originally obtained from a nickel-mediated reductive coupling
reaction of a dodecabrominated macrocyclic precursor, albeit only
in 1% yield. The present article reports on the development of this
synthetic strategy and its extension to the preparation of the [16]
and [24]­CNB analogues. In particular, our extensive investigations
on the final belt-forming, nickel-mediated reaction led to the development
of a new ligand system that provides [12]­CNB in up to 7% yield, contributing
to the commercialization of [12]­CNB. The belt structures of [12],
[16], and [24]­CNB were characterized by NMR, UV–vis, and Raman
spectroscopy as well as mass spectrometry and X-ray crystallography.
The fluorescence of the CNBs in solution displayed a remarkable dependence
on the ring size, ranging from a broad red emission ([12]­CNB) to a
narrow-band blue emission ([24]­CNB), while both features are observed
for [16]­CNB.