Viologen

The viologens are quaternary 4,4 '- bipyridinium salts, which show pronounced photochromism. By single-electron transfer to be converted into a reversible reaction in intensively colored free radicals. The herbicide paraquat dichloride ( methyl viologen ), for example, is colorless, whereas the reduction product stained deep purple. The easy formation of free radicals responsible for the high toxicity of the bipyridinium herbicides.

As caroviologens elongated electron-conducting, conjugated polyenes are denoted by pyridinium end groups according to Thomas Arrhenius. These may be used as a molecular wire.