Optically Enhanced Solid-State H-1 NMR Spectroscopy

Low sensitivity is the primary limitation to extendingnuclearmagnetic resonance (NMR) techniques to more advanced chemical andstructural studies. Photochemically induced dynamic nuclear polarization(photo-CIDNP) is an NMR hyperpolarization technique where light isused to excite a suitable donor-acceptor system, creating aspin-correlated radical pair whose evolution drives nuclear hyperpolarization.Systems that exhibit photo-CIDNP in solids are not common, and thiseffect has, up to now, only been observed for C-13 and N-15 nuclei. However, the low gyromagnetic ratio and naturalabundance of these nuclei trap the local hyperpolarization in thevicinity of the chromophore and limit the utility for bulk hyperpolarization.Here, we report the first example of optically enhanced solid-state H-1 NMR spectroscopy in the high-field regime. This is achievedvia photo-CIDNP of a donor-chromophore-acceptor moleculein a frozen solution at 0.3 T and 85 K, where spontaneous spin diffusionamong the abundant strongly coupled H-1 nuclei relays polarizationthrough the whole sample, yielding a 16-fold bulk H-1 signalenhancement under continuous laser irradiation at 450 nm. These findingsenable a new strategy for hyperpolarized NMR beyond the current limitsof conventional microwave-driven DNP.