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

The title compound, C18H14N2O2, crystallized with two independent zwitterion mol-ecules (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 mol-ecule has an E conformation with respect to the azo double bond. In each of the independent mol-ecules, an intra-molecular N-H⋯O hydrogen bond forms an S(6) ring motif. In the crystal, mol-ecules 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 inter-actions between adjacent mol-ecules involving benzene and naphthalene rings [centroid-centroid distance of 3.626 (3) Å for adjacent A mol-ecules and 3.652 (3) Å for adjacent B mol-ecules].