Role of multipole moments in electric-field-induced order of dense molecular systems.

A new model is developed to describe the orientational order of dense molecular systems under an applied external electric field as a function of the n-particle distribution functions of a system under no external perturbation. From an approximation of this expression, the effects of several variables on this orientational order, such as the microscopic properties of the oriented molecules (the molecular geometry and multipole moments) and the solvent or matrix properties, are studied. The theoretical predictions show that, for a correct description of the orientational order, quadrupole and octupole moments must be included, as they play an important role in the orientational order achieved, depending on the molecular geometry. Furthermore, to verify the validity of the model, theoretical predictions are compared with experimental results, and show a good concordance.