Nanographene Diradicals

Nanographene diradicals have emerged in the last decade as a very fruitful approach to new open-shell polycyclic aromatic and conjugated molecules with enhanced properties. These features have straightforward connections with the electronic properties of topological graphene nanoribbons as well as with graphene itself, further increasing their relevance in the organic electronic field. A set of the most known and popular nanographene diradicals has been selected and discussed from the perspective of the multiconfigurational definition of diradical character as well as with the use of the simple Hückel molecular orbital theory. Some of the actors in the present article in representation of the nanographene diradical family are acenes, zethrenes, bisphenylenes, acenoacenes, peri-acenes, oligorylene, and rhombenes. Important concepts such as nonbonding and bonding/antibonding characters, neutral covalent and ionic structures, zig-zag and arm-chair states, etc. have been discussed in relationship with the formation/stabilization of the diradical character in these molecules.