Theoretical Prediction of Benzyne-Like Species in Pyrene Diradicals

The different products that can be obtained from pyrene dehydrogenation have been studied by means of hybrid density functional theory. Most of the didehydrogenated species exhibit a diradical character. This is supported by the closeness between the geometry and energy of singlet and triplet states and the open-shell nature of the singlet state. However, three didehydrogenated species have been found to exhibit a closed-shell singlet electronic ground state. The analysis of the electronic structure, the formation energy of these didehydrogenated species, and their geometrical structure reveals that these three didehydrogenated species are better described as benzyne-like moieties; two of them are of o- and one of m-benzyne character. The two o-benzyne species have lower energies than the m-benzyne and are favored upon diradical formation. This interpretation is fully supported by the analysis of multiconfigurational wave functions and the order of stabilities confirmed by second-order multireference perturbation theory calculations. A possible implication of the reactivity of these benzyne-like species in asphaltene formation is discussed.