We report that aromatic amphiphiles based on cruciform aromatic segments self-assemble into 2-D sheet structures in aqueous environments. Notably, the aromatic amphiphile based on a pyrene unit generates fluorescence-switching 2-D sheet structures. In a pH-neutral condition, the sheets show strong excimer emission. However, upon lowering the pH the excimer emission is quenched due to loosely-packed pyrene units. Subsequent return of pH to a neutral condition leads to full recovery of the excimer emission, indicative of fully-reversible fluorescence emission switching.