Phenalenyl (C13H9) is an open-shell spin-1/2 nanographene. Using scanning tunneling microscopy (STM) inelastic electron tunneling spectroscopy (IETS), covalently-bonded phenalenyl dimers have been shown to feature conductance steps associated with singlet-triplet excitations of a spin-1/2 dimer with antiferromagnetic exchange. Here, we address the possibility of tuning the magnitude of the exchange interactions by varying the dihedral angle between the two molecules within a dimer. Theoretical methods, ranging from density functional theory calculations to many-body model Hamiltonians solved within different levels of approximation, are used to explain STM-IETS measurements of twisted phenalenyl dimers on a h-BN/Rh(111) surface. By means of first-principles calculations, we also propose strategies to induce sizable twist angles in surface-adsorbed phenalenyl dimers via functional groups, including a photoswitchable scheme. This work paves the way toward tuning magnetic couplings in carbon-based spin chains and two-dimensional lattices.
@article{arxiv.2407.11506,
title = {Conformational tuning of magnetic interactions in coupled nanographenes},
author = {Gonçalo Catarina and Elia Turco and Nils Krane and Max Bommert and Andres Ortega-Guerrero and Oliver Gröning and Pascal Ruffieux and Roman Fasel and Carlo A. Pignedoli},
journal= {arXiv preprint arXiv:2407.11506},
year = {2024}
}