Using antiferromagnetic couplers for high-spin ground states in ion radicals Original Research Article

The presence of negatively spin-polarized peripheral sites in delocalized radical ions is exploited to propose a type of direct linkage leading to stabilization of high-spin states. Ion monoradicals of anthracene, pyrene, azulene and s-indacene are taken as spin-bearing units. Pairs with close charging potentials are outlined as likely to form diradicals. Triplet stabilization is envisaged to occur from the exchange coupling of opposite-signed bridgehead π-spin densities belonging to individual radical units, e.g., 2-(9′-anthryl)pyrene and 2,2′-bipyrenyl di-ions. Results from AM1-ROHF-CI (CAS[10,10], CAS[9,9]) computations are reported, where the computational approach is first checked for adequacy with regard to the spin-density distribution of the monoions, and then employed to assess the spin states of several ionized dimers and trimers, some of which are synthetically available. The high-spin states are found to be stabilized by up to ∼300 cal mol−1, with the singlet–triplet or doublet–quartet gaps increasing for nonequilibrium conformations approaching planarity.