Molecular Ordering in Non-Liquid Crystalline versus Liquid Crystalline Materials with Special Reference to DADMBP – A Computational Analysis

A computational analysis of the molecular ordering of the non-liquid crystalline biphenyl derivative 4,4′-diamino-3,3′-dimethylbiphenyl (DADMBP) has been performed. The CNDO/2 method has been employed to compute the net atomic charge and atomic dipole components at each atomic centre. The modified Rayleigh-Schrödinger perturbation theory along with the multicentered-multipole expansion method has been employed to evaluate the long-range interactions, while a “6-exp” potential function has been assumed for short-range interactions. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible arrangements of a molecular pair have been considered. It is found that, if a suitable functional group is attached to DADMBP, so that the length to breadth ratio is increased, the molecule will show a change in the long-range order, the phase transition temperature and other liquid crystalline properties. The results are compared with those for the liquid crystalline compounds 4-(4′-ethoxyphenylazo)phenyl valerate (EPPV) and 4,4′-di-n-propoxy-azoxybenzene (DPAB).