The Intermolecular Interactions of Pyrene and its Oxides in Vacuum and in Toluene Solution

In this work, the Conformer-Rotamer Ensemble Sampling Tool, (CREST) with the underlying semi-empirical GFN2-xtb method was used for automated geometry exploration of the homodimers of pyrene, pyrene-4,5-dione, and pyrene-4,5,9,10- tetraone, along with the heterodimer of pyrene and pyrene-4,5,9,10-tetraone. Geometries and energies of the dimers were further refined at the ωB97X-D4/def2-TZVP level of theory, both in gas phase, and in toluene solution. Computations in solu- tions were handled using the CPCM (Conductor-like Polarizible Continuum Model) and SMD (Solvation Model based on Density) models. Two previously unidentified pyrene-homodimer conformations are identified, and the effects of oxidation on the geometries and energies of dimerization are explored; in general, oxidation leads to stronger intermolecular interactions, and decreased solubility in toluene. For selected dimers, DLPNO-CCSD(T)/cc-pVTZ/SMD(Toluene) energies are determined at the DFT geometries, and illustrate the accuracy of the ωB97X-D4 approach, with an MAD of 1.47 kJ/mol.