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.