Conformational tuning of magnetic interactions in coupled nanographenes

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. In a recent work, 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 record contains data that support the results discussed in the manuscript.

苯基（C₁₃H₉）是一种具有开放壳层自旋1/2的纳米石墨烯。通过扫描隧道显微镜（STM）非弹性电子隧穿光谱（IETS）技术，共价键合的苯基二聚体表现出与自旋1/2二聚体的反铁磁交换相关的单重态-三重态激发相关的导电阶跃。在最近的研究中，我们探讨了通过调节二聚体中两个分子之间的二面角来调整交换作用强度可能性。我们采用了从密度泛函理论计算到在多种近似水平上求解的多体模型哈密顿量等理论方法，以解释在h-BN/Rh(111)表面上的扭曲苯基二聚体的STM-IETS测量结果。通过第一性原理计算，我们还提出了通过官能团诱导表面吸附苯基二聚体产生显著扭曲角的方法，包括一种光控开关方案。本记录包含支持论文中讨论的结果的数据。