Abstract
Triangular zigzag nanographenes, such as triangulene and its π‐extended homologues, have received widespread attention as organic nanomagnets for molecular spintronics, and may serve as building blocks for high‐spin networks with long‐range magnetic order, which are of immense fundamental and technological relevance. As a first step towards these lines, we present the on‐surface synthesis and a proof‐of‐principle experimental study of magnetism in covalently bonded triangulene dimers. On‐surface reactions of rationally designed precursor molecules on Au(111) lead to the selective formation of triangulene dimers in which the triangulene units are either directly connected through their minority sublattice atoms, or are separated via a 1,4‐phenylene spacer. The chemical structures of the dimers have been characterized by bond‐resolved scanning tunneling microscopy. Scanning tunneling spectroscopy and inelastic electron tunneling spectroscopy measurements reveal collective singlet–triplet spin excitations in the dimers, demonstrating efficient intertriangulene magnetic coupling.
Highlights
The fusion of benzenoid rings in a triangular fashion leads to the generation of triangular zigzag nanographenes (TZNGs) for which no KekulØ valence structures can be drawn without leaving unpaired electrons.[1]
In accordance with theoretical predictions, we experimentally detected singlet–triplet spin excitations, whose strength can be tuned with the spatial separation between the triangulene units
Our results confirm that TZNGs on metal surfaces retain their high-spin magnetic ground states, and can efficiently couple to give rise to collective magnetism
Summary
The fusion of benzenoid rings in a triangular fashion leads to the generation of triangular zigzag nanographenes (TZNGs) for which no KekulØ valence structures can be drawn without leaving unpaired electrons.[1]. Direct coupling of two triangulene units through their minority sublattice atoms leads to no sublattice imbalance in the dimer (right), leading to a low-spin ground state. The dimer with the 1,3-phenylene spacer contains a net sublattice imbalance of four in the structure, leading to a high-spin ground state. Connecting two triangulene units directly through their minority sublattice carbon atoms does not produce a net sublattice imbalance in the structure, and is expected to yield an S = 0 ground state as per Ovchinnikovs rule (Figure 1 a), which could either correspond to a magnetic, open-shell singlet or a non-magnetic, closed-shell ground state. Introduction of an organic spacer in the structure serves to tune the magnetic coupling between the triangulene units, and to modify the magnetic correlations, leading to high- or low-spin ground states. Using STS and STM-based inelastic electron tunneling spectroscopy (IETS), we unraveled unambiguous spectroscopic signatures of collective magnetism in 1 and 2 in the form of singlet–triplet spin excitations
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