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.