Synthesis, characterization, and properties of [4]cyclo-2,7-pyrenylene: effects of cyclic structure on the electronic properties of pyrene oligomers.
A cyclic tetramer of pyrene, [4]cyclo-2,7-pyrenylene ([4]CPY), was synthesized from pyrene in six steps and 18% overall yield by the platinum-mediated assembly of pyrene units and subsequent reductive elimination of platinum. The structures of the two key intermediates were unambiguously determined by X-ray crystallographic analysis. DFT calculations showed that the topology of the frontier orbitals in [4]CPY was essentially the same as those in [8]cycloparaphenylene ([8]CPP), and that all the pyrene units were fully conjugated. The electrochemical analyses proved the electronic properties of [4]CPY to be similar to those of [8]CPP. The results are in sharp contrast to those obtained for the corresponding linear oligomers of pyrene in which each pyrene unit was electronically isolated. The results clearly show a novel effect of the cyclic structure on cyclic π-conjugated molecules.
Institute for Chemical Research, Kyoto University, Uji 611-0011 (Japan).
Takahiro
T
Iwamoto
Eiichi
E
Kayahara
Nobuhiro
N
Yasuda
Toshiyasu
T
Suzuki
Shigeru
S
Yamago
arenes; carbocycles; conjugation; density functional calculations; electronic structure