(E)-1-(3-Chloro-phen-yl)-2-(2-oxidonaphthalen-1-yl)diazen-1-ium.

The title zwitterion,, C16H11ClN2O, is approximately planar, the dihedral angle between the benzene ring and naphthalene ring system is 1.55 (13)°; an intra­molecular N—H⋯O hydrogen bond stabilizes the planar conformation. In the crystal, π–π stacking between the benzene ring and the naphthalene ring system of adjacent mol­ecules links the mol­ecules into supra­molecular chains running along the b axis, the centroid–centroid distance being 3.765 (2) A.