Growth and Characterization of Molecular Crystals of para-Sexiphenyl by All-Atom Computer Simulations

We present all-atom molecular dynamics computer simulations of molecular crystals of the conjugated organic molecule para-sexiphenyl (p-6P), which constitutes a popular basic molecule for optoelectronic applications. After validating single-molecule properties with ab initio calculations, we demonstrate that gradually performed simulated temperature annealing leads to the spontaneous self-assembly of p-6P molecules from the fully isotropic state into the correct room-temperature solid crystal, with only a few percent deviation from the experimental unit-cell structure. A detailed investigation of the single crystal in anisotropic Gibbs ensemble simulations yields experimentally consistent structures and solid to liquid-crystal phase behavior over a wide temperature range, providing molecular insight into nanometer-scale structural and dynamic properties of self-assembled p-6P crystals. This study thus paves the way for future investigations of the computational description of nucleation and growth mechanisms of novel p-polyphenylene derivatives in the bulk as well as at functional interfaces or heterojunctions.