The dimerization of dendrimers that contain a single 4,4′‐bipyridinium (viologen) unit, upon one‐electron reduction, is strongly enhanced by the presence of the host cucurbit[8]uril. This behavior is attributed to the formation of a stable inclusion complex between the host and two π‐stacked viologen radical‐cation guests—the one‐electron‐reduced form of viologen (see scheme).

Several new series of dendrimers containing a single redox-active 4,4'-bipyridinium (viologen) residue were synthesized and characterized. In these dendrimers, the viologen group is covalently attached to the apical position of a Newkome- or Frechet-type dendron, ranging in size from first to third generation of growth. The half-wave potentials corresponding to the two consecutive one-electron reductions of the viologen residue are affected by the size of the dendritic component. The size effects are more pronounced in the Newkome-type dendrimers and seem to result from the polarity contrast between the microenvironments provided by the solution and the internal phase of the dendrimer. Unlike in many other dendrimers having a redox-active core, the voltammetric behavior remains fast (reversible) even in third generation dendrimers. Pulse gradient stimulated echo NMR diffusion coefficient measurements on the Newkome-type dendrimers reveal that their hydrodynamic radii are relatively invariant in solvents of widely different polarities (dichloromethane to dimethyl sulfoxide). The host-guest binding interactions between the viologen residue in these dendrimers and the crown ether host bis-p-phenylene-34-crown-8 were also investigated. While in Newkome-type dendrimers the growth of the dendron caused a substantial attenuation of the binding constant values, this size effect was not observed in the Frechet-type dendrimers. These electrochemical and binding measurements underscore some of the structural differences between these two common types of dendritic architectures.

Erheblich vereinfacht wird die Dimerisierung von Dendrimeren mit einer einzigen 4,4′‐Bipyridinium(Viologen)‐Einheit nach Einelektronenreduktion durch den Wirt Cucurbit[8]uril. Als Grund dafür wird die Bildung eines stabilen Einschlusskomplexes zwischen dem Wirt und zwei π‐gestapelten Viologen‐Radikalkationen – der einelektronenreduzierten Form von Viologen – angenommen (siehe Bild).