title: Radical-cation dimerization overwhelms inclusion in [N]pseudorotaxanes.
abstract: Suppression of the dimerization of the viologen radical cation by cucurbit[7]uril (CB7) in water is a well-known phenomenon. Herein, two counter-examples are presented. Two viologen-containing thread molecules were designed, synthesized, and thoroughly characterized by (1)H DOSY NMR spectrometry, UV/Vis absorption spectrophotometry, square-wave voltammetry, and chronocoulometry: BV(4+), which contains two viologen subunits, and HV(12+), which contains six. In both threads, the viologen subunits are covalently bonded to a hexavalent phosphazene core. The corresponding [3]- and [7]pseudorotaxanes that form on complexation with CB7, that is, BV(4+)⊂(CB7)2 and HV(12+)⊂(CB7)6, were also analyzed. The properties of two monomeric control threads, namely, methyl viologen (MV(2+)) and benzyl methyl viologen (BMV(2+)), as well as their [2]pseudorotaxane complexes with CB7 (MV(2+)⊂CB7 and BMV(2+)⊂CB7) were also investigated. As expected, the control pseudorotaxanes remained intact after one-electron reduction of their viologen-recognition stations. In contrast, analogous reduction of BV(4+)⊂(CB7)2 and HV(12+)⊂(CB7)6 led to host-guest decomplexation and release of the free threads BV(2(·+)) and HV(6(·+)), respectively. (1)H DOSY NMR spectrometric and chronocoulometric measurements showed that BV(2(·+)) and HV(6(·+)) have larger diffusion coefficients than the corresponding [3]- and [7]pseudorotaxanes, and UV/Vis absorption studies provided evidence for intramolecular radical-cation dimerization. These results demonstrate that radical-cation dimerization, a relatively weak interaction, can be used as a driving force in novel molecular switches.
authors.affiliation: Centre for Science and Engineering, New York University Abu Dhabi (NYUAD), Abu Dhabi (UAE).
authors.forename: Katia
authors.initials: K
authors.lastname: Nchimi-Nono
authors.forename: Parastoo
authors.initials: P
authors.lastname: Dalvand
authors.forename: Kuldeep
authors.initials: K
authors.lastname: Wadhwa
authors.forename: Selbi
authors.initials: S
authors.lastname: Nuryyeva
authors.forename: Shaikha
authors.initials: S
authors.lastname: Alneyadi
authors.forename: Thirumurugan
authors.initials: T
authors.lastname: Prakasam
authors.forename: Albert C
authors.initials: AC
authors.lastname: Fahrenbach
authors.forename: John-Carl
authors.initials: JC
authors.lastname: Olsen
authors.forename: Zouhair
authors.initials: Z
authors.lastname: Asfari
authors.forename: Carlos
authors.initials: C
authors.lastname: Platas-Iglesias
authors.forename: Mourad
authors.initials: M
authors.lastname: Elhabiri
authors.forename: Ali
authors.initials: A
authors.lastname: Trabolsi
mesh_terms: D002412:Cations; D019281:Dimerization; D008958:Models, Molecular; D015394:Molecular Structure; D043862:Rotaxanes / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D002412:Cations; D043862:Rotaxanes
keywords: electrochemistry; host-guest systems; molecular recognition; pseudorotaxanes; radical ions