Unusual electrochemical properties of unsymmetric viologen dendrimers

A new series of redox-active dendrimers containing a single 4,4'-bipyridinium (viologen) group covalently attached to the focal point of Newkome-type dendrons (first to third generation) has been prepared and characterized. The electrochemical properties of these unsymmetric dendrimers show two unusual aspects. First, the electrochemical kinetics for viologen reduction remains fast from the first to the third dendrimer generation. Second, the values of the half-wave potentials reveal that dendrimer growth favors the generation of positive charge in the viologen residue in CH(2)Cl(2), THF, and CH(3)CN solutions, while slightly disfavors it in DMSO.