Structural and computational study of reversibly photoswitchable (E)-4-((4-alkoxyphenyl)diazenyl)benzonitrile-based liquid crystals

Abstract

The pursuit for the discovery of photoswitchable materials is of great interest due to the growing demand for smart stimuli-responsive materials. Thereby, (E)-4-((4-alkoxyphenyl)diazenyl)benzonitrile derivatives, AZN-n (n = 3–12) were synthesized and characterized by FTIR and NMR (¹H and ¹³C) spectroscopies and PXRD. The structural analysis by SCXRD suggests the involvement of weak hydrogen bonds and π⋯π contacts in the crystal packing. The various interactions present and their contribution to the total interactions were described by the Hirshfeld surface as well as its 2D fingerprint plot. The energy framework analysis revealed the major contribution of the dispersion component to the total interaction energies. In addition, the nature of the short π⋯π contacts, as well as the hydrogen bonds and the charge transfer in the intermolecular interactions were well illustrated by NCI, QTAIM and NBO calculations. Furthermore, the liquid crystalline (LC) characteristics were examined by DSC and hot-stage POM analysis, revealing the appearance of a nematic phase, with the occurrence of the smectic A phase as the alkoxy chain lengthens. Again, the reversible fast photo-switching nature of these derivatives in solution as well as in the LC state was demonstrated using light irradiation of suitable wavelengths, showing their potential in the fabrication of light-controlled devices.