Bis(azuleno)pentalenes with Six Consecutive Odd‐Membered Rings

Abstract

Abstract Non‐alternant, non‐benzenoid polycyclic hydrocarbons (PHs) exhibit unique optical and electronic properties distinct from their well‐studied benzenoid π‐conjugated counterparts. However, the synthesis of such π‐systems, particularly those composed exclusively of odd‐membered carbocycles, remains a significant challenge. Herein, we report the first synthesis of three diazuleno[ a , e ]pentalene derivatives ( AP‐1 , AP‐2 , and AP‐3 ), featuring fused five‐ and seven‐membered rings, via a palladium‐catalyzed homoannulation of o ‐alkynylazulenyliodide. These compounds possess a 24 π‐electron system with six consecutively fused odd‐membered rings in a 7‐5‐5‐5‐5‐7 topology. Comprehensive characterization by X‐ray crystallography, NMR spectroscopy, and theoretical calculations (ACID, NICS) reveals an electronic structure comprising two aromatic azulene units fused to a central antiaromatic pentalene core. The resulting molecules display a small HOMO–LUMO gap and amphoteric redox behavior, arising from the interplay between the aromatic and antiaromatic subunits. Notably, AP‐1 and AP‐2 can undergo reversible protonation and deprotonation processes upon exposure to acid and base. Furthermore, solution‐processed organic field‐effect transistors based on AP‐2 show p ‐type semiconducting behavior with a maximum hole mobility of 0.72 cm 2 V −1 s −1 , demonstrating the potential of non‐alternant, non‐benzenoid PHs for applications in organic electronics.