New azobenzene-based natural fatty acid liquid crystals with low melting point: synthesis, DFT calculations and binary mixtures

2019-05-31T01:27:02Z (GMT) by M. Hagar H. A. Ahmed O. A. Alhaddad
<p>Three new groups of azobenzene liquid crystals named,4-[2-(4-substituted phenyl)diazenyl]phenyl hexdecanoate, 4-[2-(4-substituted phenyl)diazenyl]phenyl octadeca-9-enoate, and 4-[2-(4-substituted phenyl)diazenyl]phenyl octadeca-9,12-dienoate were prepared from naturally occurring fatty acids (palmitic, oleic and linoleic acids). All groups were investigated for their mesophase formation and thermal stability of pure compounds and their binary mixtures by differential scanning calorimetry (DSC), polarised light microscopy (PLM) and thermogravemetric analyses (TGA). Each group contains two compounds that differ from each other by the polar substituent X (CH<sub>3</sub>O and Cl) with different number (<i>n</i>) of carbons in the fatty alkyl chains. Molecular structures of the prepared compounds were confirmed via FT-IR, <sup>1</sup>H NMR, C<sup>13</sup> NMR and elemental analysis. Mesomorphic and thermal properties were investigated. Smectic A phase is the mesophase observed in all of the compounds prepared and their binary mixtures with low melting temperatures. Moreover, DFT calculations were discussed for the prepared compounds. The results revealed that the alkyl chain of the carboxylate part does not significantly affect on the energy difference of the FMOs as well as the thermodynamic parameters. However, the high electronegative Cl substituent has significant effect on the energy difference of the FMOs and decreases the dipole moments of the prepared compounds.</p> <p>Semictic A texture of <i>4-[2-(4-chlorophenyl)diazenyl]phenyl octadeca-9,12-dienoate at 53.5°C</i></p>