UC Santa Barbara

Solid state nuclear magnetic resonance (NMR) is a powerful technique that gives access to molecular structures and dynamics not accessible via other methods. However, the Achilles heal of NMR is the inherently low polarization of nuclei in a magnetic field in temperatures above the milli-Kelvin range, resulting in very poor sensitivity compared to other forms of spectroscopy. Fortunately, the much larger polarization of a paramagnetic electron can be transferred to the nuclei in a process known as dynamic nuclear polarization (DNP). However, the efficiency of state of the art DNP techniques drops of significantly at high magnetic fields $>$5T and fast magic angle spinning (MAS)-- conditions favourable for high resolution NMR spectroscopy. Furthermore the scope of state of the art DNP methodology has been limited to a narrow set of paramagnetic electrons, pulse sequences, and instrumentation, which has limited the widespread applicability of DNP

This dissertation will seek to enhance the efficiency of DNP high magnetic field and fast MAS via electron spin analysis and manipulation of the coupled electron spin network. Advanced DNP instrumentation was also developed and applied to novel DNP systems in an effort to expand the scope of DNP to presently "exotic" paramagnetic systems.

In an effort to rationalize DNP performance of current state of the art DNP radicals, an electron paramagnetic resonance (EPR) case study was undertaken that revealed a previously unknown distribution of magnetic spin-spin exchange coupling. The origin of this distribution was rationalized to be rotamer states via DFT calculations, and its effect on DNP was elucidated via quantum mechanical DNP simulations.

The magnetic properties of the spin system is only half the recipe for DNP, as $\mu$w irradiation of the EPR transitions is also necessary to facilitate polarization transfer. Thus, we have also developed a new method for shaped $\mu$w irradiation to boost the efficiency of DNP under MAS. This technique promises to be even more efficient compared to standard $\mu$w irradiation at higher temperatures, higher magnetic fields, and at higher $\mu$w power as new $\mu$w source technology is developed.

Finally, we have developed a new versatile cryogen free dual EPR/DNP probe for in situ EPR and NMR analysis of non-traditional DNP systems. This probe been designed to provide optimal $\mu$w (EPR) and radiofrequency (NMR) performance simultaneously for a broad range of nuclei and electron centers. This system has been used to analyze and demonstrate DNP between paramagnetic centers of different spin quantum number for the first time, opening up an entirely new avenues of DNP methodology using hetero-spin systems. The versatility of this system also allows testing of novel DNP instrumentation, as well as addition of various capabilities to enable a wide range of magnetic resonance experiments including ENDOR and light activated DNP.