Molecular Structure and Ordering in Biphenyl Molecules with Strong Polar Group: A Comparative Computational Analysis Between a Mesogen and Non-Mesogens

Abstract

The systems chosen, 4-heptyl-3'-cyanobiphenyl and 4-heptyl-4'-nitrobiphenyl are non-mesogens having strong polar group. A computational approach of ordering in these non-mesogens has been carried out with respect to translatory and orientational motions. The evaluation of net atomic charges and dipole moments at each atomic center has been carried out using the complete neglect differential overlap (CNDO/ 2) method. The modified Rayleigh-Schrodinger perturbation theory along with the multicentered-multipole expansion method has been employed to evaluate long-range interactions, while a "6-exp" potential function has been assumed for short-range interactions. All possible geometrical arrangements between a molecular pair have been considered and the most favorable stacked and in-plane energy configurations have been obtained. A comparative picture of molecular parameters, such as total energy, binding energy and total dipole moment of the non-mesogens with a mesogen 4-heptyl-4'-cyanobiphenyl has been reported. It is found that, if a suitable functional group is attached/replaced in these systems, so that the length to breadth ratio is altered, the molecule will show a change in the long-range order, the phase transition temperature. This affords a new way of looking at the substitution of suitable functional groups, which may have an effective role on anisotropic molecular interaction and other factors responsible for liquid crystallinity.