The unit cell parameters determined from the 300 K film show a triclinic structure and are very similar to those determined for 2F-EPI, suggesting a similar type of packing motif. The volume of the unit cell means that only one EPI molecule is present in the unit cell (Z = 1). On the basis of this information, molecular dynamics (MD) simulations were performed to get information regarding the orientation of the molecule within the unit cell and to obtain a crystal structure solution for EPI in the 300 K thin films. Initial structures were generated by expanding the experimentally determined unit cell volume by 20% and randomly placing one molecule within the cell. MD simulation runs over 70 ps were performed, during which the unit cell was shrunk back to the experimentally determined dimensions while the systems relaxed. The resulting structures were first ordered based on energy, before several hundred of the lowest energy structures were grouped based on similarity according to certain criteria (e.g. Hausdorff distance to the lowest energy structure, π–π interaction distance, etc.). A representative structure from each group was then further optimized using dispersion corrected density functional theory (DFT) calculations. The simulated diffraction patterns of these structures were then compared to the experimental diffraction pattern and the final structure was chosen based on a comparison of the experimentally determined and simulated structure factors (Fig. 4, middle); this structure was also the lowest energy structure obtained from the DFT optimizations. Please note that the accuracy of this crystal structure is restricted based on experimental limitations (e.g. certain corrections to the peak intensities could not be applied due to the broad and weak nature of the observed Bragg peaks) and also the sample quality (only a small number of low intensity peaks are observed). However, the fact that a previously unknown crystal structure of a material can be determined from a thin film diffraction pattern based on a very limited dataset (∼7 Bragg peaks) is worth highlighting. The final structure determined from the thin film by the MD simulations and DFT optimization is shown in Fig. 5. The structure has a layered motif of molecules hydrogen-bonded to neighbors via two N–H···O hydrogen bonds, with N···O distances of 2.68 Å (Fig. 5, left), and intermolecular π–π interactions with neighboring molecules with a distance of 3.47 Å (Fig. 5, right). The hydrogen bond distance found in the structure is relatively short, but not uncommon.45 It should also be noted that this distance is likely strongly dependent on the choice of unit cell parameters; as there is only one molecule in the unit cell, it only self-interacts with molecules in adjacent unit cells.