Inspirations for EO polymer design gained from modeling of chromophore poling by Langevin dynamics

One of the possibilities to create organic molecular material for NLO applications are polymers with dispersed NLO active chromophores. These molecules must be acentrically ordered by applying an external electric poling field. The NLO efficiency depends on dipole moment, molecular hyperpolarizabilities, concentration of the chromophores and external poling field strength. Calculating, from first principles, the extent of the alignment and via this NLO efficiency has proven to be challenging. One approach to solve this problem is pure analytic statistical mechanics treatment, what could be enhanced by Monte Carlo (MC) statistical mechanical modelling. The chromophore molecules usually have been treated as point dipoles embedded in some kind of realistic molecular shape - prolate spheroid. Another possibility is fully atomistic molecular modelling with classical force field MD methods. This method allows obtain extent of alignment and observing kinetics of poling and relaxation. Unfortunately, in case when host and chromophores are represented at atomistic level, MD approach requires huge amount of computations. One of the solutions is to reproduce the motion of the molecules of interest (chromophores) using Langevin dynamics (LD). This method simulates the effect of molecular collisions and the resulting dissipation of energy that occur in real host, without explicitly including host molecules. In this contribution chromophore load, dipole moment and poling field impact on extent of alignment and poling / relaxation dynamics of model system obtained by LD simulations will be presented. On a basis of these results we would like to come forward with some inspirations for EO polymer design.