title: Synthesis of a double helicene by a palladium-catalyzed cross-coupling reaction: structure and physical properties.
abstract: For this study, twisted π-extended helicene 1 and double helicene 2 with a helicene framework were synthesized through palladium-catalyzed C-H arylation or Suzuki-Miyaura coupling reaction. X-ray crystallography revealed grossly twisted structures that were soluble in various conventional organic solvents. Optical properties based on UV/Vis and fluorescence spectra were measured. Electrochemical properties were also studied by measurements of cyclic voltammetry in 1 and 2, which revealed their HOMO and the LUMO energies. Theoretical calculation supports their HOMO and LUMO energies and molecular orbitals. Furthermore, a racemization process of 2 predicted that the activation free energy at 300 K would be 31.8 kcal mol(-1) by DFT calculation, which indicated the static helicity at 300 K.
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531 (Japan), Fax: (+81) 72-254-9931.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Kashihara
authors.forename: Toshio
authors.initials: T
authors.lastname: Asada
authors.forename: Ken
authors.initials: K
authors.lastname: Kamikawa
keywords: CH activation; cross-coupling; double helicene; helical compounds; palladium-catalyzed