title: Oligorotaxane Radicals under Orders.
abstract: A strategy for creating foldameric oligorotaxanes composed of only positively charged components is reported. Threadlike components-namely oligoviologens-in which different numbers of 4,4'-bipyridinium (BIPY(2+)) subunits are linked by p-xylylene bridges, are shown to be capable of being threaded by cyclobis(paraquat-p-phenylene) (CBPQT(4+)) rings following the introduction of radical-pairing interactions under reducing conditions. UV/vis/NIR spectroscopic and electrochemical investigations suggest that the reduced oligopseudorotaxanes fold into highly ordered secondary structures as a result of the formation of BIPY(•+) radical cation pairs. Furthermore, by installing bulky stoppers at each end of the oligopseudorotaxanes by means of Cu-free alkyne-azide cycloadditions, their analogous oligorotaxanes, which retain the same stoichiometries as their progenitors, can be prepared. Solution-state studies of the oligorotaxanes indicate that their mechanically interlocked structures lead to the enforced interactions between the dumbbell and ring components, allowing them to fold (contract) in their reduced states and unfold (expand) in their fully oxidized states as a result of Coulombic repulsions. This electrochemically controlled reversible folding and unfolding process, during which the oligorotaxanes experience length contractions and expansions, is reminiscent of the mechanisms of actuation associated with muscle fibers.
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Yuping
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Marco
authors.initials: M
authors.lastname: Frasconi
authors.affiliation: Materials and Process Simulation Center, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States.
authors.forename: Wei-Guang
authors.initials: WG
authors.lastname: Liu
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Junling
authors.initials: J
authors.lastname: Sun
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Yilei
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Joint Center of Excellence in Integrated Nano-Systems (JCIN), King Abdul-Aziz City for Science and Technology (KACST) , P.O. Box 6086, Riyadh 11442, KSA.
authors.forename: Majed S
authors.initials: MS
authors.lastname: Nassar
authors.affiliation: Joint Center of Excellence in Integrated Nano-Systems (JCIN), King Abdul-Aziz City for Science and Technology (KACST), P.O. Box 6086, Riyadh 11442, KSA; University Research Office, Intel Corporation, Building RNB-6-61, 2200 Mission College Boulevard, Santa Clara, California 95054, United States.
authors.forename: Youssry Y
authors.initials: YY
authors.lastname: Botros
authors.affiliation: Materials and Process Simulation Center, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States.
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Wasielewski
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Stoddart