Dynamics of Magnetic Isolation and Nano-Vacuum State in Endohedral Fullerene Li ⁺ @C ₆₀

The realization of isolated quantum systems within solid-state matrices is a pivotal challenge in quantum information science. This study demonstrates the existence of a "nano-vacuum" state in lithium-ion endohedral fullerene (Li⁺@C₆₀·PF₆ ^-), where the encapsulated ion exhibits extreme magnetic isolation. Using ultrahigh field (18.79 T) solid-state NMR, we observed a ⁷Li line width of ∼50 Hz that remains invariant under magic angle spinning (MAS), indicating that the ion undergoes ultrafast isotropic motion (τ_c ≪ 10^-5 s), which completely averages quadrupolar interactions. Most significantly, we report a record-breaking spin-lattice relaxation time (<i>T</i> ₁) of approximately 1068 s. This extraordinary lifetime is rationalized by a "relaxation blockade" mechanism: the absence of spin-orbit coupling prevents phonon scattering, while the rapid "roaming" of Li⁺ and the cooperative "plastic" rotation of external PF₆ ^- anions synergistically suppress dipolar and quadrupolar relaxation channels. These findings establish Li⁺@C₆₀ as a ″thermodynamically open but magnetically closed″ system, offering a robust platform for quantum sensing.