A Negatively Curved π‐Expanded Pyracylene Comprising a Tropylium Cation.

We disclose π‐expanded pyracylenes and their cationic species comprising 7‐membered rings. The compounds were synthesized by stepwise oxidative cyclodehydrogenation to monitor the effect of successive cyclization on the structural and optoelectronic properties. As shown by X‐ray crystallography, the complete cyclization leads to a boat‐shaped scaffold featuring negative curvature provided by the 7‐membered ring. The embedded tropone unit enabled the convenient generation of a stabilized tropylium cation, showing bathochromically shifted absorption bands reaching into the near‐infrared region beyond 1000 nm. The altered structural features, supported by theoretical calculations, point towards the positively charged 7‐membered ring having aromatic character. [ABSTRACT FROM AUTHOR]