  Photochemically induced dynamic nuclear polarization (photo-CIDNP) is a
method to hyperpolarize nuclear spins using light. In most cases, CIDNP
experiments are performed at a high magnetic field and the sample is irradiated
by the light inside a nuclear magnetic resonance (NMR) spectrometer. Here we
demonstrate photo-CIDNP hyperpolarization generated in the Earth magnetic field
and under zero- to ultralow field (ZULF) conditions. Irradiating a sample for
several seconds with inexpensive light-emitting diodes produces a strong
hyperpolarization of 1H and 13C nuclear spins enhancing the NMR signals several
hundred times. The hyperpolarized spin states at the Earth field and in ZULF
are different. In the latter case, the state corresponds to the singlet order
between scalar-coupled 1H-13C nuclear spins. This state has a longer lifetime
than the state hyperpolarized at Earth field. The method is simple and
cost-efficient and should be applicable to many molecular systems known to
exhibit photo-CIDNP, including amino acids and nucleotides.
