2-​Naphthalenesulfonic acid, 6-​amino-​5-​[2-​[4-​[(2-​bromo-​1-​oxo-​2-​propen-​1-​yl)​amino]​-​2-​[(4-​methyl-​3-​sulfophenyl)​sulfonyl]​phenyl]​diazenyl]​-