1H-​Benz[e]​indolium, 3-​[6-​[(2,​5-​dioxo-​1-​pyrrolidinyl)​oxy]​-​6-​oxohexyl]​-​2-​[5-​[3-​[6-​[(2,​5-​dioxo-​1-​pyrrolidinyl)​oxy]​-​6-​oxohexyl]​-​1,​3-​dihydro-​1,​1-​dimethyl-​2H-​benz[e]​indol-​2-​ylidene]​-​1,​3-​pentadien-​1-​yl]​-​1,​1-​dimethy