Structural insight into the interactions between a cationic dye and an anionic surfactant in crystals of 9-aminoacridinium dodecyl sulfate

9-Aminoacridinium dodecyl sulfate, a salt consisting of a cationic dye and an anionic surfactant, was synthesized and structurally characterized. In the crystal packing, dodecyl sulfate anions interact via weak C–H⋯O hydrogen bonds and van der Waals interactions to form monolayers. These monolayers have a corrugated surface in which shallow and deep grooves are distinguishable. 9-Aminoacridinium cations form π-stacking columns, which are located in these grooves, and interact with dodecyl sulfate monolayers via N–H⋯O and C–H⋯O hydrogen bonds. The monolayers of dodecyl sulfate ions observed in the crystal structure of the title compound represent a new type of self-assembled monolayers of this surfactant in the crystals.