Steering Power of Perfluoroalkyl Substituents in Crystal Engineering: Tuning the π-π Distance While Maintaining the Lamellar Packing Motif for Aromatics with Various Sizes of π-Conjugation

Previously, we reported that introducing perfluoroalkyl substituents onto aromatics promotes the formation of lamellar pi-pi stacked crystalline materials with short interplanar distances. In this report, we developed a new synthetic route that effectively prepares perfluoroalkylated N-containing aromatics by eliminating a side perfluoroalkylation reaction occurring on nonsubstituted C-sp2-H sites of the corresponding bromoaromatics without regioselectivity. This results in a significant improvement of the yield of target perfluoroalkylated aromatics and facilitates the purification and scale-up processes. X-ray single crystal structural analyses show that lamellar pi-pi stacked structures with tunable interplanar distances are achieved with fused N-containing aromatics with varying sizes of a-conjugation. Both crystal structures and theoretical calculations demonstrated that the interplanar distance can be fine-tuned with the size of a-conjugation, with larger a-conjugation favoring shorter interplanar distances while still maintaining a lamellar pi-pi stacked packing motif: Compared to our previous results, we find that simply changing the perfluoroalkyl substituent positions and patterns can change molecular topology to exclusively form lamellar pi-pi stacked packing motifs through prioritization of specific steric effects. Electrochemical results and absorption spectra confirm that the band gap is reduced due to increasing pi-conjugation, and the first reduction potential exhibits a significant positive shift due to both increasing pi-conjugation and perfluoroalkylation.