What is "viologen"

n. (context organic chemistry English) Any of a class of quaternary ammonium salts derived from 4,4'-bipyridine

Viologens are toxic bi pyridinium derivatives of 4,4'-bipyridyl. The name is because this class of compounds is easily reduced to the radical mono cation, which is colored intensely blue.

Possibly the best-known viologen is paraquat, which is one of the world's most widely used herbicides.