Large Aromatic Hydrocarbon Radical Cation with Global Aromaticity and State-Associated Magnetic Activity

The stable radical cation of large aromatic hydrocarbons remains a challenge, due to the recessive aromatic character and high reactivity. Here we report the design, synthesis, and characterization of new aromatic π-radical cations from one π-electron oxidation of bay-twisted dibenzoperopyrene derivatives. Experimental observations and theoretical calculations revealed that these π-radical cations had significant resonance hybrid structures, advantageous to the spin- and charge-delocalizations over the molecular backbones and emerging global aromaticity in the distorted π-system. Therefore, they are thermodynamically stable even without fully steric protection of all C–H bonds on the carbon skeleton and can be well characterized and studied routinely at ambient conditions. Moreover, the π-radical cation materials demonstrated readily formed magnetic molecule aggregates in the solution phase, while in powder states cationic monoradical characters were manifested and in the crystalline state intermolecular through-space interactions were popular. The phenomenon of varied magnetic activity in different states is experimentally investigated by various spectral means and X-ray crystallographic analysis, assisted by DFT calculations. Our study provides an insight into the resonance hybrid effects in the design of stable large aromatic hydrocarbon radical cations and demonstrates state-associated magnetic activities for π-radical cations, which are necessary in applications as magnetic materials.