Crystallographic study of two monoazo disperse dyes with a D-π-A system

Two azo disperse dyes, 2,6-dichoro-4-nitro-4,4-N-cyanoethyl-N-benzyl-azobenzene (D1) and 3-(3-methyl-4-N-ethyl-N-benzyl-phenyldiazenyl)-5-nitro-2,1-benzisothiazole (D2), were synthesised and characterised. The crystal morphologies and single crystal structures were measured. The various packing and supramolecular interactions were described. D1 formed stellate crystals. The two benzene rings bilateral to the azo unit were not coplanar. Their dihedral angle was 75.72 degrees. They were linked by the azo unit and were twisted. The coupling-component N-substituted benzyl and benzene rings were not coplanar. The chemical structure was not the typical azo structure. A dimeric packing mode was formed between adjacent molecules in a head-to-head and tail-to-tail manner. One molecule was inserted between two dimeric molecules in a head-to-tail manner. D2 formed globe crystals. The isothiazole and benzene rings of the azo unit were coplanar, with the typical - conjugated structure. The benzene rings of the azo unit and the coupling-component N-substituted benzyl were vertical. Their torsion angle was 179.9 degrees.