Dynamic Nuclear Polarization by Electron Spins in the Photoexcited Triplet State: I. Attainment of Proton Polarization of 0.7 at 105 K in Naphthalene

A high 1 H polarization of 0.7 is attained at 105 K in a 0.32 T field by dynamic nuclear polarization using electron spins in the photoexcited triplet state. In a single crystal sample of 0.018 mol% pentacene-doped naphthalene, the 1 H polarization is built up to the ultimate value attainable by this method, corresponding to a 2.1 ×10 5 -fold enhancement of 1 H polarization as compared to the thermal equilibrium polarization. The experimental strategies and possible applications as well as extensions of this approach are discussed.