1-[4-(Diamino-methyl-eneamino-sulfon-yl)phenyl-iminiometh-yl]-2-naphtholate N,N-dimethyl-formamide disolvate.

The asymmetric unit the title compound, C(18)H(16)N(4)O(3)S·2C(3)H(7)NO, contains a mol-ecule in a zwitterionic form with a deprotonated hydroxyl group and an iminium group, and two dimethyl-formamide solvent mol-ecules. The dihedral angles of the guanidine group and the naphthyl ring system with respect to the central benzene ring are 76.04 (7) and 3.45 (9)°, respectively. The conformation of the mol-ecule may be influenced, in part, by two intra-molecular hydrogen bonds, while in the crystal structure, inter-molecular hydrogen bonds form one-dimensional chains along [010].