title: Cross-conjugated oligothiophenes derived from the (C2S)n helix: asymmetric synthesis and structure of carbon-sulfur [11]helicene.
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.
authors.affiliation: Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, USA.
authors.forename: Makoto
authors.initials: M
authors.lastname: Miyasaka
authors.forename: Andrzej
authors.initials: A
authors.lastname: Rajca
authors.forename: Maren
authors.initials: M
authors.lastname: Pink
authors.forename: Suchada
authors.initials: S
authors.lastname: Rajca
mesh_terms: D002244:Carbon / Q000737:chemistry*; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards; D008958:Models, Molecular; D015394:Molecular Structure; D011083:Polycyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D012015:Reference Standards; D013455:Sulfur / Q000737:chemistry*; D013876:Thiophenes / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D011083:Polycyclic Compounds; D013876:Thiophenes; C506736:beta-heptathiophene; C506737:beta-undecathiophene; C031660:helicenes; D013455:Sulfur; D002244:Carbon