Monte Carlo Statistical Mechanical Simulations of the Competition of Intermolecular Electrostatic and Poling-Field Interactions in Defining Macroscopic Electro-Optic Activity for Organic Chromophore/Polymer Materials

Monte Carlo statistical mechanical computer simulations of the electric-field poling of second-order nonlinear optical chromophores, characterized by large dipole moments, polarizabilities, and hyperpolarizabilities, are presented. Such theoretical analysis is critical to defining the structure/function relationships that permit maximization of electro-optic activity for π-electron chromophore-containing polymeric materials. Polymeric electro-optic materials may, in turn, be important for high-bandwidth telecommunications, new forms of radar, and high-speed data processing. The experimentally observed maxima in plots of electro-optic activity versus chromophore number density (loading) in polymer matrices are theoretically reproduced, as are the shifts of the maxima to lower loading with increasing chromophore dipole moment. Modification of the chromophore shape to realize the maximum achievable electro-optic activity for a given π-electron structure is discussed, as is the role of polymer electrical permittivity. Monte Carlo results are compared with the results of equilibrium statistical mechanical calculations based on the approximation of Piekara. The theoretical results presented here have led to the production of polymeric electro-optic materials that permit devices with drive voltage requirements of less than 1 V to be fabricated. Polymeric modulators now significantly exceed the performance capabilities (in terms of bandwidth and drive voltage) of electro-optic modulators based on inorganic materials.