Azulene

Photochemistry

Nuclear physics

Layer (electronics)

Thin-film transistor

Aromaticity

Polycyclic compound

Pentacene

Molecule

Polymer

Physics

Organic chemistry

Singlet state

Computational chemistry

Conjugated system

Excited state

Crystallography

Acene

Chemistry

Diradical

Annulene

Ring (chemistry)

Angewandte Chemie International Edition

Non‐alternant non‐benzenoid π‐conjugated polycyclic hydrocarbons (PHs) are expected to exhibit very different electronic properties from the all‐benzenoid PHs. Herein, we report the synthesis and physical properties of three azulene‐fused acene molecules ( 1 , 2 and 3 ), which are isoelectronic to the pentacene, hexacene and heptacene, respectively. X‐ray crystallographic analysis, NMR spectra, and theoretical calculations reveal a localised aromatic backbone comprising all the six‐ and five‐membered rings while the seven‐membered ring remains non‐aromatic. They display properties of both azulene and acenes and are much more stable than the respective acenes. The dications of 1 , 2 and 3 were formed by chemical oxidation. Notably, 3 2+ exhibited an open‐shell diradical character ( y 0 =30.2 %) as confirmed by variable‐temperature NMR and ESR measurements, which can be explained by recovery of aromaticity of an 2,6‐anthraquinodimethane unit annulated with two aromatic tropylium rings.

Azulene‐Fused Acenes