Strengthening π–π Interactions While Suppressing C_sp2–H···π (T-Shaped) Interactions via Perfluoroalkylation: A Crystallographic and Computational Study That Supports the Beneficial Formation of 1‑D π–π Stacked Aromatic Materials

The design and synthesis of aromatic crystalline materials with controllable crystal structure packing is of particular interest in organic semiconductor and optoelectronic devices, where 1-D π–π stacked structures that enhance charge mobility are the most beneficial. We report here that the π–π interactions between aromatic molecules can be strengthened and the C_sp2–H···π (T–shape) interaction can be suppressed by perfluoroalkylation of corresponding aromatics. Both crystal structure data and ab initio calculations show that the π–π interaction is strengthened due to the electronic effects of perfluoroalkyl substituents, and the C_sp2–H···π interaction is suppressed by the steric effects of the perfluoroalkyl substituents. The C_sp3–F···F–C_sp3 attractive interactions between perfluoroalkyl chains further stabilize the crystal structures. We also found that C_sp3–F···π interaction can be eliminated if an optimal electron deficiency of the π system is tuned by adjusting the number of perfluoroalkyl substituents. The insight gained from this study is of particular interest in organic semiconductor research as well as the fields of molecular recognition, sensing, and design of enzyme inhibitors where π–π interactions are also important