3,3' -({4-[(4,5-Dicyano-1H-imidazol-2-yl)-diazenyl]phenyl}imino)dipropionic acid

The title compound is a push–pull non-linear optical chromophore containing a dialkylamino donor group and the dicyanoimidazolyl acceptor separated by a conjugated path. The benzene and imidazole rings are not coplanar, making a dihedral angle of 10.0 (2)°. In the crystal, molecules are linked by an extended set of hydrogen bonds and several motifs are recognized. Pairs of molecules are held together by hydrogen bonding between carboxy O—H donor groups and diazenyl N-atom acceptors, forming R2,2(24) ring patterns across inversion centres. Four-molecule R4,4(28) ring motifs are formed, again across inversion centres, through hydrogen bonding involving carboxy O—H donor groups and diazenyl and imidazole N-atom acceptors. Four-molecule R4,4(42) patterns are formed among molecules related by translation and involve carboxy O—H and imidazole N—H donor groups with carbonyl O-atom and imidazole N-atom acceptors.