Structural Correlations and Percolation in Twisted Perylene Diimides Using a Simple Anisotropic Coarse-Grained Model

Large,
twisted, and fused conjugated molecular architectures have
begun to appear more prominently in the organic semiconductor literature.
From a modeling perspective, such structures present a challenge to
conventional simulation techniques; atomistic resolutions are computationally
inefficient, while traditional isotropic coarse-grained models do
not capture the inherent anisotropies of the molecules. In this work,
we develop a simple coarse-grained model that explicitly incorporates
the anisotropy of these molecular architectures, thereby providing
a route toward analyzing π-stacking, and thus qualitative electronic
structure, at a computationally efficient coarse-grained resolution.
Our simple coarse-grained model maintains relative orientations of
conjugated rings, as well as inter-ring dihedrals, that are critical
for understanding electronic and excitonic transport in bulk systems.
We apply this model to understand structural correlations in several
recently synthesized perylene diimide (PDI)-based organic semiconductors.
Twisted and nonplanar molecular architectures are found to promote
amorphous morphologies while maintaining local π-stacking. A
graph theoretical network analysis demonstrates that these twisted
molecules are more likely to form percolating three-dimensional pathways
for charge motion than strictly planar molecules, which show connectivity
in only one dimension.