1-[(E)-2-(2-Hy-droxy-5-methyl-phen-yl)diazen-2-ium-1-yl]naphthalen-2-olate.

The title zwitterion, C17H14N2O2, crystallizes with two independent mol-ecules in the asymmetric unit, both of which are approximately planar, the dihedral angles between the benzene ring and the naphthalene ring system being 4.39 (12)° in one mol-ecule and 5.83 (12)° in the other, and show an E conformation with respect to the azo double bond. An intra-molecular N-H⋯O hydrogen bond in each molecule helps to establish their near planar conformation. In the crystal, mol-ecules are linked through O-H⋯O hydrogen bonds into infinite chains running along the a-axis direction. In addition, the chains are stacked along the b axis via π-π inter-actions between the benzene and the naphthalene rings of adjacent mol-ecules, the centroid-centroid distances being 3.722 (3) and 3.823 (4) Å.