Radical‐Cation Dimerization Overwhelms Inclusion in [n]Pseudorotaxanes |
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| Authors: | Dr. Katia Nchimi‐Nono Parastoo Dalvand Dr. Kuldeep Wadhwa Selbi Nuryyeva Shaikha Alneyadi Dr. Thirumurugan Prakasam Dr. Albert C. Fahrenbach Prof. John‐Carl Olsen Dr. Zouhair Asfari Carlos Platas‐Iglesias Dr. Mourad Elhabiri Prof. Ali Trabolsi |
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| Affiliation: | 1. Centre for Science and Engineering, New York University Abu Dhabi (NYUAD), Abu Dhabi (UAE);2. Laboratoire de Chimie Bioorganique et Médicinale, UMR 7509 CNRS, Université de Strasbourg, ECPM, 25 rue Becquerel, 67200 Strasbourg (France);3. Laboratoire d'Ingénierie Moléculaire Appliquée à l'Analyse, IPHC, UMR 7178 CNRS, Université de Strasbourg, ECPM, 25 rue Becquerel, 67200 Strasbourg (France);4. Department of Chemistry, Faculty of Science, UAEU University, Al Ain (UAE);5. Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208‐3113 (USA);6. School of Sciences, Indiana University Kokomo, Kokomo, IN 46904 (USA);7. Departamanto de Quimíca Fundamental, Universidade da Coru?a, Campus da Zapateira–Rúa da Fraga 10, 15008 A Coru?a (Spain) |
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| 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 1H 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+?( CB 7)2 and HV 12+?( CB 7)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+?( CB 7)2 and HV 12+?( CB 7)6 led to host–guest decomplexation and release of the free threads BV 2( . +) and HV 6( . +), respectively. 1H 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. |
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| Keywords: | electrochemistry host– guest systems molecular recognition pseudorotaxanes radical ions |
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