Inspired by the pioneering work of Hoffmann, Imamura and Hehre (JACS 1968), we sought to better understand singlet-triplet splitting, as well as through-space and through-bond coupling, in a series of aromatic and heteroaromatic di- and poly-radicals. The ability to characterize open-shell polyradical species and the cyclization reactions that involve such molecules holds significant promise for advancing the fields of multireference theoretical chemistry, mechanistic organic chemistry, materials design and drug optimization. This talk will describe our recent work using highly correlated multireference methods to characterize the low-lying electronic states of various aromatic and heteroaromatic diradicals. In many cases, we find that these molecules possess a very high density of electronic states. For instance - in <i>p</i>-benzyne - there are more than seventeen states within 7 eV of the ground state including two 3s Rydberg states. Diradical geometries and energetic spacings provide insight into through-bond and through-space electron coupling and the role of aromaticity in the stability of these species.

Minding the gap: Quantum studies of the singlet-triplet splittings in aromatic diradicals

254th National Meeting (2017)

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