1H-​Benz[e]​indolium, 2-​[2-​[3-​[2-​[3-​(5-​carboxypentyl)​-​1,​3-​dihydro-​1,​1-​dimethyl-​2H-​benz[e]​indol-​2-​ylidene]​ethylidene]​-​1-​cyclohexen-​1-​yl]​ethenyl]​-​1,​1,​3-​trimethyl-​, inner salt