Preparation, characterization, and electrochemical properties of a new series of hybrid dendrimers containing a viologen core and Frechet and Newkome dendrons.

Five new 4,4'-bipyridinium (viologen) core dendrimers containing a Frechet (Fn, n = 1-3, first to third generation) and a Newkome (Nn, n = 1-3) dendron linked to each of the termini of the viologen residue were prepared and characterized. These macromolecules (FnNn) were prepared according to synthetic methodology already developed by our group. The electrochemical behavior of these dendrimers is characterized by the stepwise reduction of the viologen nucleus (V(2+)/V(+) and V(+)/V). The recorded half-wave potentials are affected by dendron growth in the three surveyed solvent media (dichloromethane, tetrahydrofuran, and acetonitrile). The size of the Newkome dendron has a more pronounced effect on the half-wave potentials than the size of the Frechet dendron. However, increasing the size of the Frechet dendron diminishes the magnitude of the cathodic potential shifts resulting from Newkome dendron growth. The largest dendrimers investigated (F1N3 and F2N3) exhibit quasi-reversible voltammetric behavior. The diffusion coefficients of these molecules were also determined using pulse gradient stimulated echo NMR techniques.