title: Internal dynamics in helical molecules studied by X-ray diffraction, NMR spectroscopy and DFT calculations.
abstract: The conformational behaviour of a prototype helical molecule, [6]helicene, and its derivatives was studied in solution and the solid state. Available crystal structures of [6]helicene revealed surprisingly large flexibility of this molecule and variable-temperature NMR experiments provided unusual temperature dependence of chemical shifts of hydrogen, carbon and fluorine atoms in the peripheral aromatic rings of [6]helicene and tetrafluoro[6]helicene. These chemical shift changes were interpreted as a consequence of the helicene 'pitch' opening with elevated temperature, and the experimental data were corroborated by DFT calculations of the chemical shift dependence on the helicene conformation and by variable-temperature DFT molecular dynamics simulations.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo 2, 16610 Prague, Czech Republic. dracinsky@uochb.cas.cz.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0002-4495-0070
authors.initials: M
authors.lastname: Dračínský
authors.affiliation: Institute of Chemical Process Fundamentals, Czech Academy of Sciences, Rozvojová 135, 16502 Prague, Czech Republic. sykora@icpf.cas.cz.
authors.forename: Jan
authors.initials: J
authors.lastname: Storch
authors.affiliation: Institute of Chemical Process Fundamentals, Czech Academy of Sciences, Rozvojová 135, 16502 Prague, Czech Republic. sykora@icpf.cas.cz.
authors.forename: Vladimír
authors.initials: V
authors.lastname: Církva
authors.affiliation: Faculty of Science, Charles University in Prague, Hlavova 2030, 12840 Prague, Czech Republic.
authors.forename: Ivana
authors.initials: I
authors.lastname: Císařová
authors.affiliation: Institute of Chemical Process Fundamentals, Czech Academy of Sciences, Rozvojová 135, 16502 Prague, Czech Republic. sykora@icpf.cas.cz.
authors.forename: Jan
authors.initials: J
authors.lastname: Sýkora