Synthesis and characterization of super-nonazethrene

TL;DR

This study reports the synthesis and detailed electronic characterization of super-nonazethrene, the largest zethrene derivative, revealing its open-shell singlet ground state and potential for molecular spintronics applications.

Contribution

It presents the first combined in-solution and on-surface synthesis of super-nonazethrene and demonstrates its open-shell electronic properties through advanced microscopy and spectroscopy.

Findings

Super-nonazethrene exhibits an open-shell singlet ground state.

It has a large spin polarization-driven electronic gap of 1 eV.

High intramolecular magnetic exchange coupling of 51 meV was observed.

Abstract

Beginning with the early work of Clar et al. in 1955, zethrenes and their laterally-extended homologues, super-zethrenes, have been intensively studied in the solution phase, and are widely investigated as optical and charge transport materials. Super-zethrenes are also considered to exhibit an open-shell ground state. Zethrenes may thus serve as model compounds to investigate nanoscale pi-magnetism. However, their synthesis is extremely challenging due to their high reactivity. We report here a combined in-solution and on-surface synthesis of the hitherto largest zethrene homologue - super-nonazethrene - on Au(111). Using single-molecule scanning tunneling microscopy and spectroscopy, we show that super-nonazethrene exhibits an open-shell singlet ground state featuring a large spin polarization-driven electronic gap of 1 eV. We obtain real-space maps of the frontier molecular orbitals, and find that they correspond to singly occupied molecular orbitals. In consistence with the emergence of an open-shell ground state, high-resolution tunneling spectroscopy reveals inelastic singlet-triplet spin excitations in super-nonazethrene, characterized by a strong intramolecular magnetic exchange coupling of 51 meV. Further insights are gained by mean-field and many-body perturbation theory calculations. Given the paucity of zethrene chemistry on surfaces, our results therefore provide unprecedented access to large open-shell zethrene compounds amenable to scanning probe measurements, with potential application in molecular spintronics.