4-[(5-Carboxy-1,3,3-trimethylindol-1-ium-2-yl)methylidene]-2-[[5-(dihydroxymethyl)-1,3,3-trimethylindol-2-ylidene]methyl]-3-oxocyclobuten-1-olate;[4-[5-[2-[6-(dihydroxymethyl)-3-methyl-1,3-benzothiazol-2-ylidene]ethylidene]-4-oxo-2-sulfanylidene-1,3-thiazolidin-3-yl]phenyl]phosphonic acid;3-[5-[2-(3-ethyl-1,3-benzothiazol-2-ylidene)ethylidene]-4-oxo-2-sulfanylidene-1,3-thiazolidin-3-yl]propanoic acid;2-[(2-hydroxy-3,4-dioxocyclobuten-1-yl)methylidene]-1,3,3-trimethylindole-5-carboxylic acid