(538h) Development of an Anisotropic Coarse-Grained Conjugated Polymer Model for Optoelectronic Applications

Conjugated polymers have attracted attention for their uses in a variety of optoelectronic applications; their electronic properties can be altered to meet a variety of needs by fine-tuning both molecular structure and processing conditions. Developing models for simulating conjugated polymers that are fast yet contain the fine structural details necessary for examining the influence of morphology on electronic structure are crucial for understanding how to optimize conjugated polymer processing conditions. Specifically, conventional coarse-graining techniques fail to address the anisotropic interactions of the conjugated polymer backbone fundamental to both polymer pi-stacking and optoelectronic transport. In order to address this problem, we have developed a coarse-grained conjugated polymer model wherein monomers are represented as disks that interact through an anisotropic Gay-Berne potential and the backbone is modeled as a twistable wormlike chain. These two features allow this coarse-grained model to capture the anisotropic pi-stacking and semi-flexibility properties that are crucial to understanding these polymers, while substantially simplifying computations. We have parameterized the coarse-grained model from an atomistic model of a thiophene-containing conjugated polymer through free energy surface calculations and persistence length fitting. The anisotropic structural detail, including dihedral degrees of freedom, maintained by our coarse-grained model allows for the straightforward computation of x-ray scattering profiles and other relevant correlation functions, without the need for atomistic backmapping. Moreover, the form of our coarse-grained model allows for a simple mapping to an electronic tight-binding hamiltonian wherein the electronic structure of the valence bands may be evaluated. We perform structural and optoelectronic benchmarking of our coarse-grained model and compare these results to atomistic simulations and experimental data.