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 <i>g</i>-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.