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

Abstract

Previously, we reported that introducing perfluoroalkyl substituents onto aromatics promotes the formation of lamellar π–π 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 π–π stacked structures with tunable interplanar distances are achieved with fused N-containing aromatics with varying sizes of π-conjugation. Both crystal structures and theoretical calculations demonstrated that the interplanar distance can be fine-tuned with the size of π-conjugation, with larger π-conjugation favoring shorter interplanar distances while still maintaining a lamellar π–π 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 π–π stacked packing motifs through prioritization of specific steric effects. Electrochemical results and absorption spectra confirm that the band gap is reduced due to increasing π-conjugation, and the first reduction potential exhibits a significant positive shift due to both increasing π-conjugation and perfluoroalkylation.