Cross-conjugated oligothiophenes derived from the (C2S)n helix: asymmetric synthesis and structure of carbon-sulfur [11]helicene |
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Authors: | Miyasaka Makoto Rajca Andrzej Pink Maren Rajca Suchada |
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Institution: | Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, USA. |
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Abstract: | (-)-Sparteine-mediated asymmetric synthesis of di-n-octyl-substituted carbon-sulfur 11]helicene, a helical (C2S)n beta-undecathiophene, is described. The atom-efficient routes rely on one-step tri-annelation or two-step di- and mono-annelation to provide enantiomeric excess of (+)- or (-)-11]helicene, respectively. X-ray structures for homologous 11] and 7]helicenes indicate similar helical curvatures. The optical band gap, Eg approximately 3.5 eV, is estimated for the (C2S)n helix polymer, with onset of electron localization at n = 7. |
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