3H-​Indolium, 2-​[5-​[1-​[6-​[(3-​azidopropyl)​amino]​-​6-​oxohexyl]​-​1,​3-​dihydro-​3,​3-​dimethyl-​5-​sulfo-​2H-​indol-​2-​ylidene]​-​1,​3-​pentadien-​1-​yl]​-​3,​3-​dimethyl-​5-​sulfo-​1-​(3-​sulfopropyl)​-​, inner salt