title: Synthesis, Structures, and Properties of π-Extended Double Helicene: A Combination of Planar and Nonplanar π-Systems.
abstract: The synthesis, structures, and properties of a π-extended double helicene 1 are described. This double helicene 1 was synthesized by a four-fold oxidative C-H biphenylation of naphthalene followed by the Scholl reaction or via five steps including the Suzuki-Miyaura cross-coupling reaction and the Scholl reaction. Due to the two helical substructures, 1 has three isomers, i.e., two enantiomers in a twisted form [(P,P) and (M,M)] and one diastereoisomer in a meso form. X-ray crystallographic analysis of the twisted isomers (twisted-1) revealed a tightly offset packing pattern of (P,P)- and (M,M)-twisted isomers, affording a three-dimensional lamellar stacking structure. A high isomerization barrier (43.5 kcal mol(-1)) and the relative thermal stability of twisted-1 isomer over meso-1 by 0.9 kcal mol(-1) were estimated by DFT calculations. The three isomers were successfully separated by chiral HPLC and characterized by circular dichroism spectroscopy as well as by TD-DFT studies. Electronic state variation resulting from the molecular geometry difference between the two diastereoisomers (twisted-1 and meso-1) was observed by UV-vis absorption and fluorescence spectra.
authors.affiliation: †Graduate School of Science, ‡JST, ERATO, Itami Molecular Nanocarbon Project, and §Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya 464-8602, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Fujikawa
authors.affiliation: †Graduate School of Science, ‡JST, ERATO, Itami Molecular Nanocarbon Project, and §Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya 464-8602, Japan.
authors.forename: Yasutomo
authors.initials: Y
authors.lastname: Segawa
authors.affiliation: †Graduate School of Science, ‡JST, ERATO, Itami Molecular Nanocarbon Project, and §Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya 464-8602, Japan.
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Itami
mesh_terms: D001713:Biphenyl Compounds / Q000737:chemistry; D018360:Crystallography, X-Ray; D007536:Isomerism; D008958:Models, Molecular; D009281:Naphthalenes / Q000737:chemistry; D010084:Oxidation-Reduction; D011083:Polycyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D001713:Biphenyl Compounds; D009281:Naphthalenes; D011083:Polycyclic Compounds; C031660:helicenes; C031721:naphthalene