Interface-Controlled Spin States of Phenalenyl Radicals

Understanding and controlling interfacial spin states in open-shell organic radicals is essential for developing molecule-based spintronic devices. Using spin-polarized density functional theory, we investigate the prototypical phenalenyl radical adsorbed on Au(111), Cu(111), and Pt(111) surfaces. The results reveal that substrate-dependent hybridization critically governs the magnetic behavior: weak coupling on Au preserves spin polarization, strong chemisorption on Pt quenches it, and Cu exhibits geometry-dependent partial retention. This variation originates from orbital-specific coupling between the phenalenyl frontier π orbitals and the metal d_z² states, which dictates charge redistribution and spin polarization. External electric fields and perpendicular interface tuning reveal that spin-state control is possible and fundamentally attributed to the hybridization-driven charge redistribution. Our results highlight that substrates are not passive supports but active determinants of radical spin states, providing essential insight for designing stable spin-polarized interfaces in molecular spintronics.