1-(3-Acetyl-phen-yl)-2-(2-oxidonaph-thalen-1-yl)diazen-1-ium.

The title compound, C18H14N2O2, crystallized with two independent zwitterion mol­ecules (A and B) in the asymmetric unit. They are both close to planar, the dihedral angle between the benzene ring and naphthalene ring system being 4.30 (9)° in A and 4.69 (9)° in B. Each mol­ecule has an E conformation with respect to the azo double bond. In each of the independent mol­ecules, an intra­molecular N—H⋯O hydrogen bond forms an S(6) ring motif. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds, forming –A—A—A– and –B—B—B– chains parallel to one another and propagating along the a-axis direction. There are also π–π inter­actions between adjacent mol­ecules involving benzene and naphthalene rings [centroid–centroid distance of 3.626 (3) A for adjacent A mol­ecules and 3.652 (3) A for adjacent B mol­ecules].