Catarina Gonçalo, Turco Elia, Krane Nils, Bommert Max, Ortega-Guerrero Andres, Gröning Oliver, Ruffieux Pascal, Fasel Roman, Pignedoli Carlo A
nanotech@surfaces Laboratory, Empa─Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, 3012 Bern, Switzerland.
Nano Lett. 2024 Oct 9;24(40):12536-12544. doi: 10.1021/acs.nanolett.4c03518. Epub 2024 Sep 30.
Phenalenyl (CH) 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 phenalenyl dimers on a hexagonal boron nitride (h-BN)/Rh(111) surface, which exhibit signatures of twisting. 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.
菲萘基（CH）是一种开壳层自旋1/2的纳米石墨烯。利用扫描隧道显微镜（STM）非弹性电子隧穿光谱（IETS），已证明共价键合的菲萘基二聚体具有与具有反铁磁交换的自旋1/2二聚体的单重态-三重态激发相关的电导台阶。在此，我们探讨了通过改变二聚体内两个分子之间的二面角来调节交换相互作用强度的可能性。从密度泛函理论计算到在不同近似水平下求解的多体模型哈密顿量等理论方法，被用于解释在六方氮化硼（h-BN）/Rh(111)表面上菲萘基二聚体的STM-IETS测量结果，这些测量结果显示出扭曲的特征。通过第一性原理计算，我们还提出了通过官能团在表面吸附的菲萘基二聚体中诱导可观扭曲角的策略，包括一种光开关方案。这项工作为调节碳基自旋链和二维晶格中的磁耦合铺平了道路。
