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.