Reorientation of the cation radical of heptyl viologen on mercury in water/DMSO mixed media

In aqueous mixed media containing DMSO in fractions by volume above 0.50 th e cation radical of heptyl viologen (HV.+) can be absorbed in two different orientations on a mercury electrode. Thus, the cation radical can take a p lanar conformation relative to the surface; however, depending on the appli ed potential, it can reorient itself to adopt a different conformation wher e the bipyridine group lies normal to or at an angle with the electrode. In this work, the reorientation was found to take place via a two-dimensional phase transition mechanism. The experimental conditions under which the ph enomenon occurs are analyzed.