Optical nuclear polarization molecular crystals

Applications of Optical Pumping and Polarization Techniques in NMR I. Optical Nuclear Polarization in Molecular Crystals... 

ONP (Fig. 3) in organic molecular crystals can be described as a three-step process (1) optical creation of electronic spin polarization in (transient) excited triplet states (2) polarization transfer to nearby nuclear spins and (3) accumulation of bulk nuclear spin magnetization in the (diamagnetic) ground state via spin-diffusion processes. Highly detailed theoretical descriptions and modeling of ONP processes observed in many systems can be found in the reviews mentioned above thus, only a brief overview is provided here. 

Fig. 3. Jablonski energy-level diagram typical for chromophores involved in ONP processes (specifically for pentacene in naphthalene, after Ref. [39]), showing the respective roles of optical excitation, ISC, OEP, electron-nuclear polarization transfer (here driven by mw radiation), and subsequent decay to the diamagnetic ground state. The relative populations of the triplet magnetic sublevels are given at the far right (assuming the crystal is oriented such that the long molecular axis of pentacene is parallel to the external magnetic field ).

---