1H-Benzotriazol-1-yl 4-{(E)-[4-(dimethylamino)phenyl]diazenyl}benzoate

The title compound, C21H18N6O2, was obtained as a by-product of a reaction between (E)-4-(4-dimethylaminophenylazo)benzoic acid and 2-amino-4-(2-pyridyl)-6-(6-pyridyl)-1,3,5-triazine, which has a very low solubility, under peptidic coupling conditions, using THF as solvent. The condensation reaction occurred between 1-hydroxybenzotriazole and (E)-4-(4-dimethylaminophenylazo)benzoic acid. The dihedral angle between the benzene rings in the (E)-diphenyldiazene fragment is 10.92 (13)° and that between the benzotriazole mean plane and the central benzene ring is 80.57 (7)°. In the crystal, π–π stacking [centroid–centroid distances = 3.823 (2) and 3.863 (2) ] of similar fragments generates molecular layers parallel to (0-12). The crystal packing also features weak C—H...N hydrogen bonds involving N atoms of the benzotriazole ring.