Building a Mixed Polyarene π‑Stack with Charge Disparity through Chemical Oxidation: A Structural and Theoretical Investigation

Chemical oxidation of a perylene
and coronene mixture
with GaCl3 results in the formation of a unique mixed polycyclic
aromatic
hydrocarbon (PAH) product of the composition, [(C20H12)2(C24H12)]2+(GaCl4–)2·(C6H6)2, as revealed by single crystal X-ray diffraction.
The crystal structure exhibits π-stacked columns of repeating
perylene-perylene-coronene units, with π-stacks separated by
GaCl4– anions and benzene molecules.
Interplanar contacts in the asymmetric PAH trimer average 3.352(2)
Å, with an atom-over-atom π-surface overlap between neighboring
perylene and coronene. In the solid-state, multiple H···Cl
contacts between the perylene moieties and GaCl4– anions are present, with additional C–H···π
contacts found between coronene and benzene molecules. The EPR spectrum
of the crystals shows a strong singlet with a g-factor
of 2.0041, indicative of an organic radical persistent in a very broad
temperature range. The UV–vis absorption spectra point to the
asymmetric charge distribution in the mixed PAH trimer, in accord
with core deformation revealed crystallographically. The original
crystal structure is used as a model for in-depth theoretical description
of bonding and charge assignment within a heteromolecular PAH trimer.
Computational studies reveal that the surrounding GaCl4– and benzene units play a crucial role in stabilizing
the structure and modulating the electronic properties of the perylene-perylene-coronene
stacks. Computational results also fully support the interpretation
of the uneven charge distribution based on solid-state characteristics
and spectroscopic data.