title: Hexaphyrin-Cyclodextrin Hybrids: A Nest for Switchable Aromaticity, Asymmetric Confinement, and Isomorphic Fluxionality.
abstract: Conformational control over the highly flexible π-conjugated system of expanded porphyrins is a key step toward the fundamental understanding of aromaticity and for the development of molecular electronics. We have synthesized unprecedented hexaphyrin-cyclodextrin (HCD) capped hybrids in which the hexaphyrin part is constrained in a planar rectangular conformation in either a 26 or a 28 π-electron oxidation state ([26]/[28]HCD). These structures display strong aromaticity and antiaromaticity, respectively, exhibit markedly different chiroptical properties, and are interconvertible upon the addition of DDQ or NaBH(OAc)3, thus affording a rare switchable aromatic-antiaromatic system with a free-base expanded porphyrin. Conformational analysis revealed discrimination of the two coordination sites of the hexaphyrin, one of which was coupled to a confined asymmetric environment, and fluxional behavior consisting of apparent rotation of the hexaphyrin cap through a shape-shifting mechanism.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, Institut Parisien de Chimie Moléculaire (UMR CNRS 8232; France). mickael.menand@upmc.fr.|CNRS, Institut Parisien de Chimie Moléculaire (UMR CNRS 8232), 4, place Jussieu, 75005 Paris (France). mickael.menand@upmc.fr.
authors.forename: Mickaël
authors.initials: M
authors.lastname: Ménand
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, Institut Parisien de Chimie Moléculaire (UMR CNRS 8232; France).|CNRS, Institut Parisien de Chimie Moléculaire (UMR CNRS 8232), 4, place Jussieu, 75005 Paris (France).
authors.forename: Matthieu
authors.initials: M
authors.lastname: Sollogoub
authors.affiliation: Institut des Sciences Chimiques de Rennes, UMR CNRS 6226, Université de Rennes 1, 263 avenue du General Leclerc, 35042 Rennes cedex (France).
authors.forename: Bernard
authors.initials: B
authors.lastname: Boitrel
authors.affiliation: Institut des Sciences Chimiques de Rennes, UMR CNRS 6226, Université de Rennes 1, 263 avenue du General Leclerc, 35042 Rennes cedex (France). stephane.legac@univ-rennes1.fr.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Le Gac
keywords: aromaticity; conformation analysis; cyclodextrins; degenerate equilibria; porphyrinoids