Aromatic anions with triplet ground states

Hoijtink has found aromatic anions with triplet ground states. For example, 1,3,5-triphenylbenzene reacts with potassium to give the... 

As mentioned above, triplet Cgo is readily photoreduced by amines and other donors to Cgo radical anion and the donor radical cations [64], We expected this reaction to lead to adducts with covalent bonds. Such adducts are formed with some amines in ground state chemistry [33, 60, 83], but the photochemical process should be more selective and easily controlled, since only one-electron reduction is possible in the photochemical process. C o in the Si state has been suggested to produce an exciplex with triethylamine which seems to react with ground-state Cgo to give a stable product [117]. The reduction potential of the triplet is high enough that electron-transfer from many donors such as electron-rich aromatics and alkenes should be possible. 

Gallup and Norbeck have made valence bond ab initio calculations on the electronic structure of cyclopentadienyl cation and anion with Dj symmetry. The lowest singlet- and triplet-state energies were calculated for each ion, from which it was concluded that, as expected, the cation has a 2 ground state and the anion ground state, i.e. antiaromatic and aromatic respectively. 

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