title: Relative unidirectional translation in an artificial molecular assembly fueled by light.
abstract: Motor molecules present in nature convert energy inputs, such as a chemical fuel or incident photons of light, into directed motion and force biochemical systems away from thermal equilibrium. The ability not only to control relative movements of components in molecules but also to drive their components preferentially in one direction relative to each other using versatile stimuli is one of the keys to future technological applications. Herein, we describe a wholly synthetic small-molecule system that, under the influence of chemical reagents, electrical potential, or visible light, undergoes unidirectional relative translational motion. Altering the redox state of a cyclobis(paraquat-p-phenylene) ring simultaneously (i) inverts the relative heights of kinetic barriers presented by the two termini--one a neutral 2-isopropylphenyl group and the other a positively charged 3,5-dimethylpyridinium unit--of a constitutionally asymmetric dumbbell, which can impair the threading/dethreading of a [2]pseudorotaxane, and (ii) controls the ring's affinity for a 1,5-dioxynaphthalene binding site located in the dumbbell's central core. The formation and subsequent dissociation of the [2]pseudorotaxane by passage of the ring over the neutral and positively charged termini of the dumbbell component in one, and only one, direction relatively defined has been demonstrated by (i) spectroscopic ((1)H NMR and UV/vis) means and cyclic voltammetry as well as with (ii) DFT calculations and by (iii) comparison with control compounds in the shape of constitutionally symmetrical [2]pseudorotaxanes, one with two positively charged ends and the other with two neutral ends. The operation of the system relies solely on reversible, yet stable, noncovalent bonding interactions. Moreover, in the presence of a photosensitizer, visible-light energy is the only fuel source that is needed to drive the unidirectional molecular translation, making it feasible to repeat the operation numerous times without the buildup of byproducts.
authors.affiliation: Department of Chemistry, ‡Department of Chemistry and Argonne-Northwestern Solar Energy Research Center, and §Department of Materials Science and Engineering, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Hao
authors.initials: H
authors.lastname: Li
authors.forename: Chuyang
authors.initials: C
authors.lastname: Cheng
authors.forename: Paul R
authors.initials: PR
authors.lastname: McGonigal
authors.forename: Albert C
authors.initials: AC
authors.lastname: Fahrenbach
authors.forename: Marco
authors.initials: M
authors.lastname: Frasconi
authors.forename: Wei-Guang
authors.initials: WG
authors.lastname: Liu
authors.forename: Zhixue
authors.initials: Z
authors.lastname: Zhu
authors.forename: Yanli
authors.initials: Y
authors.lastname: Zhao
authors.forename: Chenfeng
authors.initials: C
authors.lastname: Ke
authors.forename: Juying
authors.initials: J
authors.lastname: Lei
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Young
authors.forename: Scott M
authors.initials: SM
authors.lastname: Dyar
authors.forename: Dick T
authors.initials: DT
authors.lastname: Co
authors.forename: Ying-Wei
authors.initials: YW
authors.lastname: Yang
authors.forename: Youssry Y
authors.initials: YY
authors.lastname: Botros
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
authors.forename: Michael R
authors.initials: MR
authors.lastname: Wasielewski
authors.forename: R Dean
authors.initials: RD
authors.lastname: Astumian
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Stoddart
mesh_terms: D008027:Light; D020409:Molecular Motor Proteins / Q000737:chemistry*
chemical_list: D020409:Molecular Motor Proteins