Cyclopenta‐Fused Polyaromatic Hydrocarbon (CP‐PAH) Radicals: Synthesis, Characterization, and Quantum Chemical Calculations

Abstract Two air‐ and moisture‐stable cyclopenta‐fused polyaromatic hydrocarbon (CP‐PAH) radicals with six six‐ and three five‐membered rings alternately fused to nonacycles were obtained by ortho fusion in suitably ortho , ortho ’‐substituted dinaphthylfluorenes and subsequent establishment of the conjugation. The radicals were obtained in five consecutive steps with total yields of 38 and 16%, respectively; key steps are Suzuki couplings and cyclizing S E Ar reactions. Mesityl substituents at the five‐membered rings ensure the kinetic stability of the radicals. They were characterized by EPR and UV/Vis spectroscopy. Quantum chemical calculations led to simulated UV/Vis/NIR spectra and disclosed further properties like spin densities, aromaticity, and orbital energies. Both radicals are best described with the unpaired electron centered in the outer five‐membered rings. The respective resonance formulas show the largest number of fully intact benzene rings. A possible triradical character was computed to be small in both compounds. The five‐membered rings, especially the central rings show significant antiaromatic character.