title: Folding of oligoviologens induced by radical-radical interactions.
abstract: We report the synthesis of a series of homologous oligoviologens in which different numbers of 4,4'-bipyridinium (BIPY(2+)) subunits are linked by p-xylylene bridges, as a prelude to investigating how their radical cationic forms self-assemble both in solution and in the solid state. The strong radical-radical interactions between the radical cationic forms of the BIPY(2+) units-namely, BIPY(•+)-in these oligoviologens induce intra- or intermolecular folding of these homologues. UV/Vis/NIR spectroscopic studies and DFT quantum mechanics indicate that the folding of the shorter oligoviologens is dominated by intermolecular radical-radical interactions. In addition to intermolecular interactions, strong intramolecular radical-radical interactions, which give rise to an NIR absorption band at 900 nm, tend to play a crucial role in governing the folding of the longer oligoviologens. The solid-state superstructure of the oligoviologen with three BIPY(2+) units reveals that two intertwining chains fold together to form a dimer, stabilized by intermolecular radical-radical interactions. These dimers continue to stack in an infinite column through intermolecular radical-radical interactions between them. This research features an artificial biomimetic system which sustains delicate secondary and tertiary structures, reminiscent of those present in nucleic acids and proteins.
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.forename: Marco
authors.initials: M
authors.lastname: Frasconi
authors.forename: Wei-Guang
authors.initials: WG
authors.lastname: Liu
authors.forename: Zhichang
authors.initials: Z
authors.lastname: Liu
authors.forename: Amy A
authors.initials: AA
authors.lastname: Sarjeant
authors.forename: Majed S
authors.initials: MS
authors.lastname: Nassar
authors.forename: Youssry Y
authors.initials: YY
authors.lastname: Botros
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Stoddart
mesh_terms: D015195:Drug Design; D005609:Free Radicals / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry*; D014755:Viologens / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D011108:Polymers; D014755:Viologens