Tailoring π--d$\pi {\text{--}}d$ Magnetic Interactions in Metallated Porphyrin Nanotapes

Molecular assemblies based on porphyrins (Pors), specifically Por nanotapes (NTs) containing magnetic metal ions, offer a versatile platform to explore magnetic interactions arising from the electronic interplay between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:semantics><mml:mi>π</mml:mi> <mml:annotation>$\pi$</mml:annotation></mml:semantics> </mml:math> -conjugated ligands and transition metal d-orbitals. Using on-surface synthesis under ultra-high vacuum, we synthesized <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:semantics><mml:mi>π</mml:mi> <mml:annotation>$\pi$</mml:annotation></mml:semantics> </mml:math> -extended PorNTs of different lengths incorporating magnetic metal ions such as Fe and Co on Au(111). We resolved their atomic structure using scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). Differential conductance ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>d</mml:mi> <mml:mi>I</mml:mi> <mml:mo>/</mml:mo> <mml:mi>d</mml:mi> <mml:mi>V</mml:mi></mml:mrow> <mml:annotation>${\rm d}I/{\rm d}V$</mml:annotation></mml:semantics> </mml:math> ) measurements, interpreted by extensive density functional theory calculations and theoretical modeling, reveal two distinct magnetic behaviors for the Fe- and Co-based systems. In FePorNTs, the magnetic interactions are dominated by strong Fe-ligand ferromagnetic coupling and weak antiferromagnetic Fe-Fe coupling. By contrast, CoPorNTs exhibit stronger Co-Co antiferromagnetic exchange and weaker Co-ligand coupling, with Kondo screening evident at the ligand sites. Our findings underscore the profound influence of metal centers, ligands, and substrate interactions on the magnetic and electronic properties of PorNTs, establishing these assemblies as interesting building blocks for low-dimensional magnetism and future spintronic or quantum-material applications.