Steering Large Magnetic Exchange Coupling in Nanographenes near the Closed-Shell to Open-Shell Transition

作者：Kalyan Biswas, Diego Soler, Shantanu Mishra, Qiang Chen, Xuelin Yao, Ana Sánchez‐Grande, Kristjan Eimre, Pingo Mutombo, Cristina Martín‐Fuentes, Koen Lauwaet, José M. Gallego, Pascal Ruffieux, Carlo A. Pignedoli, Kläus Müllen, Rodolfo Miranda, José I. Urgel, Akimitsu Narita, Román Fasel, Pavel Jelı́nek, David Écija · 发表于：Journal of the American Chemical Society · 年份：2023 · DOI：10.1021/jacs.2c11431 · 被引用次数：59 · 研究领域：Graphene research and applications、Molecular Junctions and Nanostructures、Quantum and electron transport phenomena

The design of open-shell carbon-based nanomaterials is at the vanguard of materials science, steered by their beneficial magnetic properties like weaker spin–orbit coupling than that of transition metal atoms and larger spin delocalization, which are of potential relevance for future spintronics and quantum technologies. A key parameter in magnetic materials is the magnetic exchange coupling (MEC) between unpaired spins, which should be large enough to allow device operation at practical temperatures. In this work, we theoretically and experimentally explore three distinct families of nanographenes (NGs) ( A, B, and C ) featuring majority zigzag peripheries. Through many-body calculations, we identify a transition from a closed-shell ground state to an open-shell ground state upon an increase of the molecular size. Our predictions indicate that the largest MEC for open-shell NGs occurs in proximity to the transition between closed-shell and open-shell states. Such predictions are corroborated by the on-surface syntheses and structural, electronic, and magnetic characterizations of three NGs ( A[3,5], B[4,5], and C[4,3] ), which are the smallest open-shell systems in their respective chemical families and are thus located the closest to the transition boundary. Notably, two of the NGs ( B[4,5] and C[4,3] ) feature record values of MEC (close to 200 meV) measured on the Au(111) surface. Our strategy for maximizing the MEC provides perspectives for designing carbon nanomaterials...