1-(4-Cyano-phenyl-diazen-2-ium-1-yl)-2-naphtholate.

In the mol-ecule of the zwitterionic title compound, C(17)H(11)N(3)O, the naphthalene ring system is planar [maximum deviation = 0.029 (3) Å] and is oriented at a dihedral angle of 3.55 (3)° with respect to the benzene ring. An intra-molecular N-H⋯O hydrogen bond results in the formation of a planar six-membered ring. In the crystal structure, inter-molecular C-H⋯O inter-actions link the mol-ecules into centrosymmetric dimers.