Cucurbit[7]uril (CB7  )'s suppression of viologen radical cation dimerization in water is a well-known phenomenon. Here, we present two counter-examples. We have designed, synthesized, and thoroughly characterized (by 1H DOSY NMR spectrometry, UV-Vis absorption spectrometry, square wave voltammetry (SWV), and chronocoulometry) two viologen-containing thread molecules: BV4+ , which contains two viologen subunits and HV12+  , which contains six. In each, the viologens are covalently bonded to a hexavalent phosphazene core. We have also analyzed the corresponding [3]- and [7]pseudorotaxanes that form upon complexation with CB7  : BV  4+�(CB  7)2   and HV  12+�(CB  7)6  , and for comparison, we investigated the properties of two momomeric control threads, methyl viologen (MV2+)  and benzyl methyl viologen (BMV2+  ) and their [2]pseudorotaxane complexes with CB7  : MV2+  �CB7  and BMV2+  �CB7  . As expected, the control pseudorotaxanes remain intact after one-electron reduction of their viologen recognition stations. In contrast, analogous reductions of either BV  4+�(CB  7)2  or HV  12+�(CB  7)6  lead to host-guest decomplexation and release of the free threads, BV2(�+)  or HV6(�+)  , respectively. 1H DOSY NMR spectrometric and chronocoulometric measurements show that BV2(�+)  and HV6(�+)  have larger diffusion coefficients than the corresponding [3]- and [7]pseudorotaxanes, and UV-Vis absorption studies provide 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

Redox-controlled composition of viologen-based molecular switches

248th National Meeting (2014)

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