Characterization of Strongly Hyperfine-split Protons by DNP

How the polarization transfer from the electron spin to the nuclear spins in such experiments proceeds and which nuclear spins close to an unpaired electron get polarized and contribute through spin diffusion to the observable bulk nuclear magnetization is not fully understood.

We address these questions by combining reverse DNP and band-selective inversion pulses on nuclear spins. We report the electron-detected NMR spectrum of proton spins involved in the direct DNP process in Ox063 trityl samples with protonated and deuterated solvents and variable radical con- centrations. We also determine the spin-diffusion barrier surrounding trityl and estimate the spectral diffusion barrier to encompass spins outside ν0,I ∈14.69,15.07 MHz for a bulk proton frequency of 14.853 MHz.