Influence of delocalization on the stability of dianions: study of a systematic series of dianions with growing electronic localization

The electronic stability of a dianion is influenced by the degree of delocalization of its electrons, but it is generally not possible to separate this influence from other effects. Here, we investigate by theoretical means the sequence of dianions consisting of phen-1,4-ylenbis(ethynide) and seven of its derivatives obtained by hydrogenating the benzene core in several steps. These dianions are structurally similar and mainly differ by the degree of delocalization of their electrons. We present geometries and electron detachment energies computed at a correlated level of theory. The results point to a classification of the eight dianions in three distinct groups of electronic stability. We are able to explain this grouping by a simple resonance structure picture, which demonstrates why the dianions with more delocalized electrons are less stable.