title: Functionalized thiophene-based [7]helicene: chirooptical properties versus electron delocalization.
abstract: The functionalized, enantiomerically pure [7]helicene 1 derived from bis(benzodithiophene) functionalized with four heptyl groups is prepared from 1,8-dibromo-4,5-diheptylbenzo[1,2-b:4,3-b']dithiophene building block 2. Such [7]helicene structure, functionalized with bromines at the terminal positions of the helicene inner rim and multiple solubilizing alkyl groups, is an attractive building block for long [n]helicenes and oligo[7]helicenes. Chirooptical properties and the degree of electron delocalization are determined and compared to those of analogous carbon-sulfur [7]helicene and [7]helicenes derived from benzodithiophene to provide a correlation between chirooptical properties and the degree of electron delocalization. [7]Helicene 1 possesses a moderately increased electron delocalization, but its chirooptical properties are similar to those for analogous [7]helicenes with relatively lower electron delocalization, indicating that chirooptical properties are not significantly affected by electron delocalization for this series of [7]helicenes. Molecular structures of racemic [7]helicene 1 and its benzodithiophene building block 2 are confirmed by single-crystal X-ray analysis. Crystals of 2 are chiral and adopt the shape of long, flexible, flat needles that can be readily bent.
authors.affiliation: Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, USA. arajca1@unl.edu
authors.forename: Andrzej
authors.initials: A
authors.lastname: Rajca
authors.forename: Maren
authors.initials: M
authors.lastname: Pink
authors.forename: Shuzhang
authors.initials: S
authors.lastname: Xiao
authors.forename: Makoto
authors.initials: M
authors.lastname: Miyasaka
authors.forename: Suchada
authors.initials: S
authors.lastname: Rajca
authors.forename: Kausik
authors.initials: K
authors.lastname: Das
authors.forename: Kristin
authors.initials: K
authors.lastname: Plessel
mesh_terms: D018360:Crystallography, X-Ray; D004583:Electrons; D008958:Models, Molecular; D015394:Molecular Structure; D011083:Polycyclic Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D013876:Thiophenes / Q000737:chemistry*
chemical_list: D011083:Polycyclic Compounds; D013876:Thiophenes; C031660:helicenes