The Study of the properties of the calamitic liquid crystals with biphenily core by using the methods of NM and QM

The synthesis of new liquid crsytalline (LC) compounds and the determination of theproperties of these mesogen molecules have gained considerable attention in the last decadedue to the widespread use of such materials in display devices. The most interesting featuresof these materials are their small size and less power use. Since the macroscopic properties ofsuch compounds are related to their chemical structures, quantum mechanical calculations areneeded in order to design new LC strucres that have specific properties.In this study, with the intention of modifying the properties of 4-n-Pentyl-4?-cyanobiphenyl(5CSB), one and two halogen atoms, F, Cl and Br are attached on the aromatic core as lateralsubstituents. The most stable conformer for each of the 29 mono and disubstituted derivativesof 5CSB by carriying out a conformer search by means of the molecular mechanics MMFFmethods. Geometry optimizations of the most stable conformers have been performed withthe Density Functional Theory DFT by the hybrid B3LYP functional by using 6-31G* basisset.The optimum geometric parameters, thermodynamic and electronic properties of themolecules have been calculated.The results show that the lateral substituents do not have much effect on the geometricparameters but they increase the stability of the molecules investigated. Moreover, the lateralhalogen atoms modify the charge distribution causing an increase in the dipole moments.Thus, the nematic phase stability of the mesogen molecules investigated increases dependingupon the electronegativities and the sizes of the attached halogen atoms.