Cross-plane magnetic coupling in carbon-based diradicals with one-electron σ-bond regulated by conjugative substituent engineering

Abstract

The direct evidence of carbon–carbon one-electron σ-bonds marks a significant breakthrough in carbon-based materials; however, the spin coupling properties between such bonds and other spin sources in coexisting structures remain unexplored. In this work, we propose a molecular engineering strategy to modify the hexaphenylethane derivatives that contain both a carbon–carbon one-electron σ-bond (σ_C·C) and an additional spin source (a radical group). By introducing substituents with conjugative effects, we induce cross-plane spin polarization, thereby modulating the spin–spin coupling between the two spin sources. These substituents regulate the distribution of the unpaired electrons within the π-system via a push–pull effect, enabling fine-tuning of the magnetic coupling interaction between the σ_C·C and an additional radical group. Results indicate that the unsubstituted structure exhibits weak ferromagnetic (FM) coupling (J = 75.46 cm⁻¹). Notably, the introduction of substituents not only significantly alters the magnitude of magnetic coupling but also modifies the magnetic nature, with the magnetic coupling constant J spanning a wide range from −720.74 cm⁻¹ to 416.28 cm⁻¹. Molecular orbital analyses reveal that substituents influence the singly occupied molecular orbitals (SOMOs) through extended conjugation, modifying both the energy gap and spatial overlap of the two SOMOs, and thus tailoring the magnetic behavior. These findings demonstrate an effective strategy for indirect magnetic regulation in the non-planar carbon-based spintronic materials.