Diradical character view of energy stabilization in π-stacked dimers of antiaromatic molecules

Abstract We theoretically examined the energy stabilization mechanism of closely π-stacked dimers of antiaromatic molecules from the viewpoint of diradical character (y). Quantum chemical calculations for π-stacked dimer models of cyclobutadienes and Ni(II) norcorroles revealed that the balance between the destabilization due to structural deformation in each monomer and the stabilization due to intermolecular orbital interaction between 4nπ systems and dispersion force determined the stabilization in the π-dimer structures.