title: Donor-acceptor oligorotaxanes made to order.
abstract: Five donor-acceptor oligorotaxanes made up of dumbbells composed of tetraethylene glycol chains, interspersed with three and five 1,5-dioxynaphthalene units, and terminated by 2,6-diisopropylphenoxy stoppers, have been prepared by the threading of discrete numbers of cyclobis(paraquat-p-phenylene) rings, followed by a kinetically controlled stoppering protocol that relies on click chemistry. The well-known copper(I)-catalyzed alkyne-azide cycloaddition between azide functions placed at the ends of the polyether chains and alkyne-bearing stopper precursors was employed during the final kinetically controlled template-directed synthesis of the five oligorotaxanes, which were characterized subsequently by (1)H NMR spectroscopy at low temperature (233 K) in deuterated acetonitrile. The secondary structures, as well as the conformations, of the five oligorotaxanes were unraveled by spectroscopic comparison with the dumbbell and ring components. By focusing attention on the changes in chemical shifts of some key probe protons, obtained from a wide range of low-temperature spectra, a picture emerges of a high degree of folding within the thread protons of the dumbbells of four of the five oligorotaxanes-the fifth oligorotaxane represents a control compound in effect-brought about by a combination of C-H···O and π-π stacking interactions between the π-electron-deficient bipyridinium units in the rings and the π-electron-rich 1,5-dioxynaphthalene units and polyether chains in the dumbbells. The secondary structures of a foldamer-like nature have received further support from a solid-state superstructure of a related [3]pseudorotaxane and density functional calculations performed thereon.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA.
authors.forename: Subhadeep
authors.initials: S
authors.lastname: Basu
authors.forename: Ali
authors.initials: A
authors.lastname: Coskun
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Friedman
authors.forename: Mark A
authors.initials: MA
authors.lastname: Olson
authors.forename: Diego
authors.initials: D
authors.lastname: Benítez
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Tkatchouk
authors.forename: Gokhan
authors.initials: G
authors.lastname: Barin
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Yang
authors.forename: Albert C
authors.initials: AC
authors.lastname: Fahrenbach
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Stoddart
mesh_terms: D002384:Catalysis; D003300:Copper / Q000737:chemistry; D018360:Crystallography, X-Ray; D004583:Electrons; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons; D043862:Rotaxanes / Q000138:chemical synthesis* / Q000737:chemistry*
chemical_list: D011522:Protons; D043862:Rotaxanes; D003300:Copper