Solid-phase transitions of polymorphs of 4-(4-N,N-dialkylaminophenyl)azobiphenyl-2,3’,4’-tricarbonitriles and their analogues

A new series of push–pull azo-dyes containing tricyanodiphenyl electron-withdrowing block, namely (4-N,N-dialkylaminophenyl)azobiphenyl-2,3’,4’-tricarbonitriles, was proposed and synthesized. The azo-dyes possess high temperature stability and are prone to form polymorph modifications. DSC measurements indicated solid-phase transitions of these polymorphs. X-ray diffraction (XRD) analysis revealed that in all solved structures, there is a network of short intermolecular contacts between H_Arom atoms and N atoms of cyano groups. The supramolecular structure of these contacts depends on the alkyl chain length in the aniline moiety, and changes after temperature induced phase transitions.