New calamitic thermotropic liquid crystals of 2-hydroxypyridine ester mesogenic core: mesophase behaviour and DFT calculations

ABSTRACT

New three groups of 2-hydroxypyridine ester-based liquid crystals named, 5-[2-(4-substitutedphenyl)diazenyl]pyridin-2-yl 4?-alkoxybenzoate were synthesised. Each group differs from each other by the terminal polar substituent X (CH₃O, Cl and H) which contains five compounds with different numbers (n) of carbons in the alkoxy chain. Mesophase behaviour was investigated for the prepared homologues by differential scanning calorimetry and polarised light microscopy. Elemental analyses, FTIR and ¹HNMR spectroscopy were used for structure confirmation of the prepared compounds. Density functional theory (DFT) theoretical calculations are estimated to prove the experimental data. Stability ranges and the type of the mesophases observed for the investigated compounds were found to be mainly dependent on the length of the alkoxy chain, the polarity, as well as dipole moment and charge distribution. Moreover, the high terminal charge distribution in the case of the methoxy derivative could effect the end-to-end interactions resulting in a nematic phase rather than the ordered Smectic A phase observed in the case of Cl derivatives and the unsubstituted homologues which are non-mesomorphic. Results of the DFT discussed are found to be consistent with the present experimental investigations.