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Experimental and theoretical approaches of new nematogenic chair architectures of supramolecular H-bonded liquid crystals
1 , * 2
1  Faculty of Science, Department of Chemistry, Cairo University, Cairo, Egypt.
2  Taibah University


New four isomeric chair architectures of 1:1 H-bonded supramolecular complexes were prepared through intermolecular interactions between 4-(2-(pyridin-4-yl)diazenyl-(2-(or 3-)chlorophenyl) 4-alkoxybenzoates and 4-n-alkoxybenzoic acids. The H-bond formation of all complexes was confirmed by differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). Mesomorphic characterization was carried by DSC and polarized optical microscopy (POM). It was found that, all prepared laterally choro substituted supramolecular complexes were nematogenic exhibited pure nematic phase and low melting temperature. The thermal stability of the nematic mesophase observed depends upon the location and spatial orientation of the lateral Cl- atom in as well as the length of terminal chains. A comparison between the new investigated 1:1 mixtures and previously reported laterally CH3 as well as the laterally neat complexes revealed that, the position/orientation and polarity of incorporated lateral group into the azopyridine component enhance the entropy changes and affect on the type and stability of the mesophase. The density functional theory (DFT) theoretical calculations were discussed to predict the molecular conformation for the formed complexes as well as their thermal parameters. The results of the computational calculations revealed that the H-bonded complexes were in a chair form molecular geometry. Moreover, the results explained the effect the position and orientation of the lateral group as well as the alkoxy chain length on the type and the stability of the nematic mesophase. In addition, their impacts on the estimated thermal parameters of H-bonded complex and how these play an important role in influencing thermal and optical properties.

Keywords: Chair – shaped supramolecular liquid crystals; Hydrogen bonding; Azopyridines; Nematic phase; DFT theoretical calculations; Molecular geometry