Hyperpolarization of Thin Films with Dynamic Nuclear Polarization Using Photoexcited Triplet Electrons

With dynamic nuclear polarization using the photoexcited triplet electron spin (triplet-DNP) of pentacene, nuclear spins can be hyperpolarized even in a low magnetic field at room temperature. Several demonstrations have been performed using bulk crystals. Hyperpolarization in a thin film with triplet-DNP enables new applications, such as general NMR spectroscopy and the polarized target of unstable nuclei. In this work, we succeeded in polarizing H-1 spins in a thin film fabricated by the cell method. We obtained a H-1 spin polarization of 12.9% using a 7-mu m-thick film of p-terphenyl doped with pentacene in 0.4 T at room temperature. We also obtained a H-1 spin polarization of 3.9% in 0.4 T at 150 K using a 60-mu m-thick film of trans-stilbene doped with pentacene, whose single crystal cannot be made easily by conventional methods.