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 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 Csp2–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.