Magnetism-tunable oligoacene dioxide diradicals: promising magnetic oligoacene-like molecules

Graphene oxide has attracted intense research interest recently because the graphene oxide synthesis route, as a promising alternative for cost-effective mass production of graphene, has been explored. To further study the oxidation process and possible mechanism and to explore applicability of the oxidized products, we have performed a computational study on three series of oligoacene dioxides, focusing on their structures and electronic properties. Taking 1,5-dioxidized naphthalene as a starting point, three series of oligoacene dioxides are considered as follows: 1) middle insertion by 1-2 benzene rings; 2) single-side expansion using 1-2 benzene rings; 3) double-side expansion using two benzene rings. On the basis of density functional theory and complete active space self-consistent field (CASSCF) calculations, we reveal that oligoacene dioxides in the middle insertion series have a triplet ground state, whereas those in the single-side expansion series and the double-side expansion series have open-shell broken-symmetry singlet diradical ground states except for their common origin naphthalene-1,5-dioxide whose ground state is triplet and which is also viewed as the origin of the middle insertion series. Magnetic coupling interactions of these oligoacene dioxides are also determined. This work should help people toward an atomistic understanding of the electronic structures and properties of possible intermediates or products and even the oxidation mechanism of graphene sheets, and provides a reasonable strategy of designing novel graphene-oxide-based magnetic materials.