Atomic-Scale Control of π-Electron Magnetism in Metal-Free Phthalocyanine: A Theoretical Study

Abstract Recent progress in on-surface synthesis of carbon-based π-electron magnetic materials has established a promising platform for applications in spintronics and quantum technologies. Nonetheless, a critical challenge remains in the precise generation and modulation of delocalized π-electron magnetism within these nanoscale quantum magnets. In this study, we propose an effective approach to address this challenge in phthalocyanine species through coordination chemistry. Specifically, nonmagnetic metal-free phthalocyanine (H2Pc) molecules adsorbed on Au(111) surfaces can manifest delocalized π-electron magnetism by controlling the number of hydrogen atoms adsorbed at the pyridinic nitrogen sites of the molecule. First-principles calculations corroborate the emergence of spin-polarized singly occupied molecular orbital (SOMO) states, which are induced by intramolecular charge transfer from the adsorbed hydrogen atoms. Moreover, this π-electron magnetism can be reversibly switched on or off via selective hydrogenation. Importantly, the delocalized net spins distributed over the Pc ring can also be screened by the conduction electrons of the substrate, resulting in a π-electron Kondo resonance. These findings demonstrate precise tunability of π-electron magnetism in metal-free phthalocyanine molecules, providing a foundation for the design of novel magnetic functionalities in phthalocyanine-based systems.