The molecule is an arenesulfonic acid, the disodium salt of which is the histological dye 'methyl blue' (used for staining collagen in Masson's trichrome and Mallory's method for connective tissue). It is an arenesulfonic acid, an imine, an aromatic amine and a secondary amino compound. It is a conjugate acid of a methyl blue(2-).
4-[4-[[4-(4-sulfoanilino)phenyl]-[4-(4-sulfophenyl)iminocyclohexa-2,5-dien-1-ylidene]methyl]anilino]benzenesulfonic acid