Benzo[e]pyrene Skeleton Dipyrylium Dication with a Strong Donor-Acceptor-Donor Interaction, and Its Two-Electron Reduced Molecule

The donor–acceptor–donor (D–A–D) conjugated molecules 1,4‐bis(diarylaminophenylethynyl)anthraquinone (1,4‐Am2Aq) and 1,4‐bis(ferrocenylethynyl)anthraquinone (1,4‐Fc2Aq), undergo a double proton cyclization reaction with bis(trifluoromethanesulfone)imide acid (TFSIH) to yield 1,4‐bis(diarylaminophenyl or ferrocenyl) dipyrylium salts [1,4‐R2Pyl2](TFSI)2 (R=Am or Fc) with novel planar pentacyclic structures similar to the aromatic benzo[e]pyrene‐type skeleton. [1,4‐Am2Pyl2](TFSI)2 could be reduced to give the neutral molecule [1,4‐Am2Pyl2]0, which is stable and maintains the benzo[e]pyrene‐type skeleton. To the best of our knowledge, this is the first oxygen‐atom‐containing polycyclic aromatic hydrocarbon with 22 (4n+2) π‐electrons. The obtained condensed‐ring benzo[e]pyrene‐type skeleton compounds show physical and chemical properties that are significantly different from those of [1,5‐Am2Pyl2](TFSI)2, which has a perylene‐type skeleton. Pentacyclic dipyrilium: The donor–acceptor–donor (D–A–D) conjugated molecules 1,4‐R2Aq (R=Am or Fc) undergo a double proton cyclization reaction with acid to yield the dipyrylium salts [1,4‐R2Pyl2](TFSI)2 with novel planar pentacyclic structures (see scheme). The obtained condensed‐ring benzo[e]pyrene‐type skeleton compounds show physical and chemical properties that are significantly different from those of [1,5‐Am2Pyl2](TFSI)2, which has a perylene‐type skeleton. (Aq=ethynylanthraquinone, Am=diarylaminophenyl, Fc=ferrocenyl.)