Thionine

Thionine is a heterocyclic organic compound belonging to the thiazine dye family. It is a metachromatic dye, meaning its color changes depending on the concentration or the medium in which it is dissolved. In dilute solutions, thionine appears blue, while in concentrated solutions, it may appear reddish-purple.

Thionine is commonly used as a biological stain, particularly for staining nucleic acids in microscopy. It binds to DNA and RNA, allowing for visualization of these molecules in tissues and cells. It's also used as a photosensitizer in photodynamic therapy and in various chemical redox reactions.

The chemical formula for thionine is C₁₂H₁₀N₃S⁺, typically encountered as a chloride salt. The core structure features a tricyclic arrangement including benzene and thiazine rings.