Ordering of N-(4-n-butyloxybenzylidene)-4′-n-ethylaniline at nematic-isotropic transition temperature:: A computational analysis

A computational analysis of ordering in liquid crystalline compound N-(4-n-butyloxybenzylidene)4'-n-ethylaniline (40.2) was carried out based on quantum mechanics and intermolecular forces. The evaluation of atomic charge and dipole moment at each atomic center was performed through the all-valence electron (CNDO/2) method. A modified Rayleigh-Schr6dinger perturbation theory was used along with the multicentered-multipole expansion method to evaluate long-range intermolecular interactions while a "6-exp" potential function was assumed for short-range interactions. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration at room temperature (300 K), the nematic-isotropic transition temperature (337.8 K), and the above-transition temperature (450 K) by the Maxwell-Boltzmann formula. The various possible configurations during the different modes (i.e., stacking, inplane, and terminal) of interaction were studied in terms of the variation of probability due to small departures from the most probable configurations. A model was developed to describe the characteristic features of liquid crystallinity in terms of their relative order with the molecular parameters introduced in this paper.