Role of electron spin dynamics and coupling network in designing dynamic nuclear polarization

Abstract

Dynamic nuclear polarization (DNP) has emerged as a powerful sensitivity booster of nuclear magnetic resonance (NMR) spectroscopy for the characterization of biological solids, catalysts and other functional materials, but is yet to reach its full potential. DNP transfers the high polarization of electron spins to nuclear spins using microwave irradiation as a perturbation. A major focus in DNP research is to improve its efficiency at conditions germane to solid-state NMR, at high magnetic fields and fast magic-angle spinning. In this review, we highlight three key strategies towards designing DNP experiments: time-domain "smart" microwave manipulation to optimize and/or modulate electron spin polarization, EPR detection under operational DNP conditions to decipher the underlying electron spin dynamics, and quantum mechanical simulations of coupled electron spins to gain microscopic insights into the DNP mechanism. These strategies are aimed at understanding and modeling the properties of the electron spin dynamics and coupling network. The outcome of these strategies is expected to be key to developing next-generation polarizing agents and DNP methods.

Keywords: Cross effect; EPR; Landau-Zener; MAS DNP; Microwave; Quantum mechanical simulation; Radical-development; Thermal mixing.