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.