Unravelling the Open-Shell Character of Peripentacene on Au(111)

Polycyclic aromatic hydrocarbons (PAHs) are a family of organic compounds comprising two or more fused aromatic rings which feature manifold applications in modern technology. Among these species, those presenting an open-shell magnetic ground state are of particular interest for organic electronic, spintronic, and non-linear optics and energy storage devices. Within PAHs, special attention has been devoted in recent years to the synthesis and study of the acene and fused acene (periacene) families, steered by their decreasing HOMO-LUMO gap with length and predicted open-shell character above some size. However, an experimental fingerprint of such magnetic ground state has remained elusive. Here, we report on the in-depth electronic characterization of isolated peripentacene molecules on a Au(111) surface. Scanning tunnelling spectroscopy, complemented by computational investigations, reveals an antiferromagnetic singlet ground state, characterized by singlet-triplet inelastic excitations with an experimental effective exchange coupling (J(eff)) of 40.5 meV. Our results deepen the fundamental understanding of organic compounds with magnetic ground states, featuring perspectives in carbon-based spintronic devices.

Automated summary

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds with multiple fused aromatic rings, some of which exhibit open-shell magnetic ground states. Recent research has focused on the synthesis and study of acene and fused acene (periacene) families, with experimental evidence of a magnetic ground state reported for isolated peripentacene molecules. This discovery contributes to a better understanding of organic compounds with magnetic properties, particularly in the development of carbon-based spintronic devices.