Up to 16% Optical Carbon-13 Hyperpolarization of Donor-Acceptor Molecules at 14.1 T

Solid-state nuclear magnetic resonance (NMR) is a powerful technique for structure determination with applications ranging from biology to material sciences. However, its inherent low sensitivity prevents many applications. In solids, optical hyperpolarization techniques such as solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) could alleviate this limitation, by generating nuclear spin hyperpolarization. We recently showed that ¹H and ¹³C photo-CIDNP can be observed for synthetic donor-acceptor (D-A) molecules. However, polarization levels in these systems are so far relatively low (<6%). In this study, we introduce a new D-A molecule for ¹³C solid-state photo-CIDNP, AnthraPol, which yields steady-state signal enhancements of up to a factor -4500 at 14.1 T, corresponding to a nuclear polarization of ∼16%. We combine magnetic field dependent experiments and numerical simulations to demonstrate possible new rational design principles for solid-state photo-PAs, which guided the identification of AnthraPol as a suitable D-A system, and which led here to threefold improved signal enhancement over the previously reported CarboPol. By comparing bulk ¹³C enhancements, we also show that these local differences in polarization are directly reflected in the bulk signal enhancement.