title: Structure, NMR and Electronic Spectra of [m.n]Paracyclophanes with Varying Bridges Lengths (m, n = 2-4).
abstract: Extending our earlier studies on cyclophanes, we here report the structure, chemical shifts, spin-spin coupling constants, absorption and emission properties of [m.n]paracyclophanes, m, n = 2-4, obtained using a combination of experimental and computational techniques. Accurate values of proton chemical shifts as well as of JHH for the bridges are determined. The experimental chemical shifts, coupling constants, absorption and emission wavelengths are satisfactorily reproduced using density functional theory calculations, using both the B3LYP and ωB97X-D functionals. The geometries predicted using a functional that includes dispersion corrections (ωB97X-D) are in a better agreement with available experimental values than those obtained using the B3LYP method. Up to 8 UV-vis absorption/emission bands have been observed (or anticipated in the region below 200 nm) and assigned on the basis of quantum-chemical calculations. Optimized excited-state geometries showed that the distances between the aromatic bridgehead carbon atoms of all the [m.n]paracyclophanes in the excited state decrease compared to the ground-state geometries by ca. 0.2-0.9 Å, the largest being for [4.4]paracyclophane, though the rather large differences in the calculated emission wavelength compared to experiment cast some doubts on the accuracy of the excited-state geometries.
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland.|Centre for Theoretical and Computational Chemistry, Department of Chemistry, UiT The Arctic University of Norway , 9037 Tromsø, Norway.
authors.forename: Taye B
authors.initials: TB
authors.lastname: Demissie
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland.
authors.forename: Helena
authors.initials: H
authors.lastname: Dodziuk
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland.|Faculty of Mathematics and Natural Sciences, College of Science, Cardinal Stefan Wyszyński University , Dewajtis 5, 01-815 Warsaw, Poland.
authors.forename: Jacek
authors.initials: J
authors.lastname: Waluk
authors.affiliation: Centre for Theoretical and Computational Chemistry, Department of Chemistry, UiT The Arctic University of Norway , 9037 Tromsø, Norway.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Ruud
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland.
authors.forename: Mariusz
authors.initials: M
authors.lastname: Pietrzak
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland.
authors.forename: Volha
authors.initials: V
authors.lastname: Vetokhina
authors.affiliation: Institute of Organic Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland.
authors.forename: Sławomir
authors.initials: S
authors.lastname: Szymański
authors.affiliation: Institute of Organic Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw, Poland.
authors.forename: Jarosław
authors.initials: J
authors.lastname: Jaźwiński
authors.affiliation: Institut für Organische Chemie, Technische Universität Braunschweig , Hagenring 30, D-38106, Braunschweig, Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Hopf