Mesomorphic and trans-cis-trans photoisomerization studies of 4-[2-(4-hexyloxyphenyl)diazenyl]phenyl alkanoates

In this paper a full new homologues series of 4-[2-(4-hexyloxyphenyl)diazenyl]phenyl alkanoates is presented. All 15 synthesized compounds are mesogenic. Using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD) measurements four mesophases (nematic, smectic C, G and H) were identified. Moreover, with ultraviolet (UV) irradiation the photoisomerization was induced. Next the process of thermal relaxation in the dark was studied by using the UV-visible (UV-Vis) spectroscopy. The data gathered allowed us to calculate the kinetic constant of the photoisomerization. Additionally, the trans and cis isomers were separated by using column gel chromatography and their UV-Vis spectra were measured.