The solid-state photo-CIDNP effect and its analytical application : photo-CIDNP MAS NMR to study radical pairs.

Photochemically induced dynamic nuclear polarization (photo-CIDNP) is an effect that produces non-Boltzmann nuclear spin polarization which can be observed as modification of signal intensity in NMR spectroscopy. The effect is well known in liquid-state NMR where it is explained most generally by the classical radical pair mechanism (RPM). In the solid-state, other mechanisms are operative in the spin-dynamics of radical pairs such as three-spin mixing (TSM) and differential decay (DD). Initially the solid-state photo-CIDNP effect has been solely observed on natural photosynthetic reaction centers (RCs). Therefore the analytical capacity of the method has been explored in experiments on reaction centers (RCs) of the purple bacterium of Rhodobacter (R.) sphaeroides. Here we will provide an account on phenomenology, theory, and analytical capacity of the solid-state photo-CIDNP effect.