New two rings Schiff base liquid crystals; ball mill synthesis, mesomorphic, Hammett and DFT studies

New analogues series of two rings Schiff base comprising different terminal polar substituents changed between N(CH3)2, CH3O, H, Cl, F, CN and NO2 were prepared using conventional heating and a ball-milling method. An alkoxy chain substituent contributes one end of their molecular structure. Mesomorphic and optical properties as well as their thermal stability were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). FT-IR, 1H NMR, 13C NMR, and elemental analysis were carried out to elucidate and confirm the molecular structures of the synthesized compounds. The mesophase type and stability of the prepared compounds are rationalized based on the varying Van der Waal volume and polarizability of the terminal groups as well as the intermolecular interactions. After compiling all resulting experimental data and discussing it in the performance of Hammett and Density functional theoretical estimated parameters, it found that the molecular structure and the dipole moment as well as the polarizability of the prepared compounds are highly affected by the electronic nature of the terminal substituent X rather than its volume. Moreover, the mesophase type and its stability were explained in the term of the DFT data and Hammett as well as Van der Waal's volume of the terminal substituents. •A new Schiff base series was prepared by ball milling method.•The molecular structures are affected by the terminal substituent X.•The mesophase behaviour depends mainly on the size and polarity of terminal group.•The high dipole moment of the NO2 derivative and the least of the terminally neat compound explain their non mesomorphic behaviors.•The charge distribution impacts the type and stability of the mesophases.