Radical‐Cation Dimerization Overwhelms Inclusion in [n]Pseudorotaxanes. Issue 24 (7th May 2014)

• Record Type: Journal Article
• Authors: Nchimi‐Nono, Katia; Dalvand, Parastoo; Wadhwa, Kuldeep; Nuryyeva, Selbi; Alneyadi, Shaikha; Prakasam, Thirumurugan; Fahrenbach, Albert C.; Olsen, John‐Carl; Asfari, Zouhair; Platas‐Iglesias, Carlos; Elhabiri, Mourad; Trabolsi, Ali
• Is Part Of: Chemistry. Volume 20:Issue 24(2014)
• Page Start: 7334
• Page End: 7344
• Publication Date: 2014-05-07
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201400069
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Suppression of the dimerization of the viologen radical cation by cucurbit[7]uril (<bold>CB7</bold>) 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 <sup>1</sup>H DOSY NMR spectrometry, UV/Vis absorption spectrophotometry, square‐wave voltammetry, and chronocoulometry: <bold>BV</bold><sup>4+</sup>, which contains two viologen subunits, and <bold>HV</bold><sup>12+</sup>, 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 <bold>CB7</bold>, that is, <bold>BV</bold><sup>4+</sup>⊂(<bold>CB</bold>7)<sub>2</sub> and <bold>HV</bold><sup>12+</sup>⊂(<bold>CB</bold>7)<sub>6</sub>, were also analyzed. The properties of two monomeric control threads, namely, methyl viologen (<bold>MV</bold><sup>2+</sup>) and benzyl methyl viologen (<bold>BMV</bold><sup>2+</sup>), as well as their [2]pseudorotaxane complexes with <bold>CB7</bold> (<bold>MV</bold><sup>2+</sup>⊂<bold>CB7</bold> and <bold>BMV</bold><sup>2+</sup>⊂<bold>CB7</bold>) were also investigated. As expected, the control pseudorotaxanes remained intact after one‐electron reduction of their viologen‐recognition stations. In contrast, analogous reduction of <bold>BV</bold><sup>4+</sup>⊂(<bold>CB</bold>7)<sub>2</sub> and <bold>HV</bold><sup>12+</sup>⊂(<bold>CB</bold>7)<sub>6</sub> led to host–guest decomplexation and release of the free threads <bold>BV</bold><sup>2(</sup><bold><sup>.</sup></bold><sup>+)</sup> and <bold>HV</bold><sup>6(</sup><bold><sup>.</sup></bold><sup>+)</sup>, respectively. <sup>1</sup>H DOSY NMR spectrometric and chronocoulometric measurements showed that <bold>BV</bold><sup>2(</sup><bold><sup>.</sup></bold><sup>+)</sup> and <bold>HV</bold><sup>6(</sup><bold><sup>.</sup></bold><sup>+)</sup> 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.</p> </abstract>