On-surface synthesis and collective spin excitations of a triangulene-based nanostar

TL;DR

This paper reports the synthesis of a triangulene-based nanostar on a gold surface, revealing collective spin excitations and antiferromagnetic interactions among unpaired electrons, providing a platform to study spin modes in cyclic systems.

Contribution

It introduces a new triangulene nanostar synthesized via on-surface methods, demonstrating collective spin states and excitations consistent with the Heisenberg model.

Findings

Observation of three spin excitations connecting singlet and triplet states.

The nanostar exhibits antiferromagnetic ordering of S=1 sites.

Behavior closely matches predictions from the Heisenberg model.

Abstract

Triangulene nanographenes are open-shell molecules with predicted high spin state due to the frustration of their conjugated network. Their long-sought synthesis became recently possible over a metal surface. Here, we present a macrocycle formed by six [3]triangulenes, which was obtained by combining the solution synthesis of a dimethylphenyl-anthracene cyclic hexamer and the on-surface cyclodehydrogenation of this precursor over a gold substrate. The resulting triangulene nanostar exhibits a collective spin state generated by the interaction of its 12 unpaired {\pi}-electrons along the conjugated lattice, corresponding to the antiferromagnetic ordering of six S = 1 sites (one per triangulene unit). Inelastic electron tunneling spectroscopy resolved three spin excitations connecting the singlet ground state with triplet states. The nanostar behaves close to predictions from the Heisenberg model of a S = 1 spin ring, representing a unique system to test collective spin modes in cyclic systems.