1H-Benz[e]indolium,3-(5-carboxypentyl)-2-[5-[3-(5-carboxypentyl)-1,3-dihydro-1,1-dimethyl-7-sulfo-2H-benz[e]indol-2-ylidene]-1,3-pentadien-1-yl]-1,1-dimethyl-7-sulfo-,inner salt, potassium salt (1:1)