Investigation of structures and liquid crystal properties of bent core mesogens by quantum mechanical methods

Liquid crystals LCs are the aggregate states of matter whose properties are intermediate between a crystaline solid and an isotropic liquid. The liquid crystals flow like a liquid, but due to their anisotropy they may have positional and/or orientational order as solids. This unusual feature gives rise to materials with unique magnetic and mechanical properties switchable under the influence of external stimuli. Thus, they are used in almost all commercially available LC displays.In recent years, owing to their outstanding properties such as ferroelecricity, antiferroelectricity and the formation of chiral mesophases from achiral molecules, bent-core or banana-shaped liquid crystals have become a new class of materials in the field of liquid crystals. The characteristic feature of such molecules is their bent shape which allows them to be arranged in smectic layers. Liquid crystal properties of bent-core LC molecules depend upon their molecular structure and intermolecular forces. Although most of the newly synthesized bent-core liquid crystal molecules are structurally very similar, each has its own specific combination of structural moieties which determine their physical properties. However, there is a very limited experimental data on the properties and behavior of bent-core mesogens. Therefore, theoretical computations are needed to predict and explain the behavior of bent-core LC molecules in terms of their molecular structures.In this study, with the intention of determining the effects of substituents, alkoxy chain lengths and branching the structures of 8 sets of 1,3-phenylene bis [4-4 - (methoxy) benzyloxy]benzoate type molecules with different substituents and variable alkoxy chain lengths from 1 to 8 carbon atoms were investigated computationally. The most stable conformer for each of the molecules was determined by carrying out a conformer analysis by means of molecular mechanics MMFF calculations. Geometry optimizations of the most stable conformers were performed with the semiempirical PM3 followed by the Density Functional Theory DFT method. The DFT calculations were carried out by the hybrid B3LYP functional with 6-31G(d) basis set. The optimum geometric parameters, thermodynamic and electronic properties of the molecules were calculated. Based on the results of the quantum mechanical calculations, the effects of the substituents, core size, molecular length, dipole moment on the characteristic bending angle were determined.