Computational Investigations of Perylene and Perylothiophene Packing

The self-assembly of small aromatic molecules into structures that exhibit long-range order is important to a variety of materials problems from fouling oil pipelines to the efficiencies of organic photovoltaics. We conduct coarse-grained molecular dynamics simulations of perylene (P1) and perylo[1,12-b,c,d]thiophene (P2) using flexible and rigid models to quantify how chemistry and model details influence self-assembly, phase behavior, and performance. We find melting transition temperatures in agreement with experiments for P1 and P2 and show that the rigid and flexible models produce identical morphologies at experimentally relevant state points. We find that ordered hexagonally-packed columnar phases are thermodynamically favorable over a wide range of densities and temperatures in both P1 and P2. We discuss similarities and differences between our simulated P1 morphologies and herringbone crystals observed in experiments. The sulfur in P2 leads to an increased melting temperature and tighter columnar packings compared to that of P1. We determine that the rigid model is more computationally efficient, with more timesteps accessible per second and generally faster relaxation and structural autocorrelation times. Yet, in a non-negligible number of cases the rigid model results in longer relaxation and autocorrelation times than their flexible counterparts.