Breaking bonds, Forming Nanographene Diradical with Pressure

New anthanthrone-based polycyclic scaffolds possessing peripheral crowed quinodimethanes have been prepared. While the compounds adopt a closed-shell butterfly shaped structure in the ground state, a concave-to-convex fluxional dynamic inversion is accessible with a low energy barrier through an open-shell diradicaloid transition-state. Mainly driven by the release of strain
attributed to the steric hindrance at the peri position of the anthanthrone core, a low-lying open-shell diradical is accessible through planarization of the core, which can be achieved by thermal excitation in solution. Alternatively, planarization can be achieved by application of mild pressure in the solid state, in which case the diradical remains kinetically trapped in an excited open-shell
configuration. Cross-information from quantum chemistry, Raman
spectroscopy and magnetic experiments allow us to corroborate these
hypotheses and determine that the resulting nanographene-like
structure possess unpaired electrons mainly localized at the exoanthanthrene
carbons bearing phenyl substituents.