Abstract
New two isomeric homologues series of dipyridine derivative liquid crystalline H-bonded complexes were formed through 2:1 intermolecular hydrogen bonding between 4-n-alkoxybenzoic acids and 4-(2-(pyridin-3-or-4-yl)diazenyl)phenyl nicotinate. The thermal and optical behaviours of these supramolecular H-bonded complexes were analysed through differential scanning calorimetry (DSC) and polarising optical microscopy (POM). The molecular structure of the new dipyridine bases were confirmed via elemental analysis, FT-IR,
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H-NMR,
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C-NMR spectroscopy. On the other hand, the formation of H-bonded supramolecular complexes was confirmed by the presence of Fermi bands in the FT-IR spectroscopy. DFT theoretical calculations of the predicted molecular geometry for the two present isomeric series were discussed. The results of the DFT calculations revealed that the orientation of the dinitrogen atoms of the dipyridine bases I and II for both H-bonded series affects many important parameters for the optical properties. Base I gives angular H-bonded complexes of higher energy and less softer than that of base II which gives linear complexes. The DFT calculations and the experimental results showed that the mesophase stability, geometrical confirmation are highly changed by the geometry of the H-bonded complexes. Moreover, their architectures change the phase from monotropic SmC phase observed in group IA-E to enantiotropic nematic mesophase for IIA-E.