3H-​Indolium, 1-​[6-​[[2-​(2,​5-​dihydro-​2,​5-​dioxo-​1H-​pyrrol-​1-​yl)​ethyl]​amino]​-​6-​oxohexyl]​-​2-​[2-​[3-​[2-​(1,​3-​dihydro-​1,​3,​3-​trimethyl-​5-​sulfo-​2H-​indol-​2-​ylidene)​ethylidene]​-​1-​cyclohexen-​1-​yl]​ethenyl]​-​3,​3-​dimethyl-​5-​