3H-Indolium, 2-[7-[1-[6-[[2-(2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl)ethyl]amino]-6-oxohexyl]-1,3-dihydro-3,3-dimethyl-5-sulfo-2H-indol-2-ylidene]-1,3,5-heptatrien-1-yl]-1-ethyl-3,3-dimethyl-5-sulfo-, inner salt