Production of High, Long-Lasting, Dynamic Proton Polarization by Way of Photoexcited Triplet States

In a crystal of fluorene ${\mathrm{C}}_{13}$ ${\mathrm{H}}_{10}$ doped with phenanthrene ${\mathrm{C}}_{14}$ ${\mathrm{D}}_{10}$ a proton spin polarization of 42% has been obtained by means of microwave-induced optical nuclear polarization involving the photoexcited triplet state of the guest. This result makes the system a promising candidate for frozen targets and for the study of magnetic ordering of nuclear spins, where the paramagnetic centers used in conventional dynamic nuclear polarization cause great complications.