Long-lived states involving a manifold of fluorine-19 spins in fluorinated aliphatic chains

Long-lived states (LLSs) have lifetimes $T_{\mathrm{LLS}}$ that exceed longitudinal spin-lattice relaxation times $T_1$ . In this study, lifetimes $T_{\mathrm{LLS}}$ (¹⁹F) have been measured in three different achiral per- and polyfluoroalkyl substances (PFAS) containing two or three consecutive CF₂ groups. In a static magnetic field $B_0=11.7$ T, the lifetimes $T_{\mathrm{LLS}}$ (¹⁹F) exceed the longitudinal relaxation times $T_1{(}^{19}$ F) by about a factor of 2. The lifetimes $T_{\mathrm{LLS}}$ (¹⁹F) can be strongly affected by binding to macromolecules, a feature that can be exploited for the screening of fluorinated drugs. Both $T_{\mathrm{LLS}}$ (¹⁹F) and $T_1$ (¹⁹F) should be longer at lower fields where relaxation due to the chemical shift anisotropy (CSA) of ¹⁹F is less effective, which is demonstrated here by running experiments at two fields of 11.7 and 7 T.