title: When a single hole aligns several spins: double exchange in organic systems.
abstract: The double exchange is a well-known and technically important phenomenon in solid state physics. Ionizing a system composed of two antiferromagnetically coupled high-spin units, the ground state of which is a singlet state, may actually produce a high-spin ground state. This work illustrates the possible occurrence of such a phenomenon in organic chemistry. The here-considered high-spin units are triangulenes, the ground state of which is a triplet. Bridging two of them through a benzene ring produces a molecular architecture of singlet ground state. A careful exploitation of a series of unrestricted density functional calculations enables one to avoid spin contamination in the treatment of the doublet states and shows that under ionization the system becomes of quartet multiplicity in its ground state. The possibility to align more than three spins from conjugated hydrocarbon polyradicals is explored, considering partially hydrogenated triangulenes. A dramatic example shows that ionization of a singlet ground state molecule may generate a decuplet.
authors.affiliation: Laboratoire de Chimie et Physique Quantiques, CNRS, UMR 5626, IRSAMC, Université Paul-Sabatier, 118 Rte de Narbonne, 31062 Toulouse Cedex, France.
authors.forename: Georges
authors.initials: G
authors.lastname: Trinquier
authors.affiliation: Laboratoire de Chimie et Physique Quantiques, CNRS, UMR 5626, IRSAMC, Université Paul-Sabatier, 118 Rte de Narbonne, 31062 Toulouse Cedex, France.
authors.forename: Vijay Gopal
authors.initials: VG
authors.lastname: Chilkuri
authors.affiliation: Laboratoire de Chimie et Physique Quantiques, CNRS, UMR 5626, IRSAMC, Université Paul-Sabatier, 118 Rte de Narbonne, 31062 Toulouse Cedex, France.
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Malrieu