Low-field photochemically induced dynamic nuclear polarization (photo-CIDNP) of diazanaphthalenes

Abstract

Photoreduction of some diazanaphthalenes in proton-donor solvents has been investigated by means of chemically induced dynamic nuclear polarization (CIDNP). While very few polarizations are observed during irradiation in a high magnetic field, CIDNP spectra recorded after the samples have been irradiated in a weak magnetic field demonstrate strong polarizations due to the solvent and the starting compounds. Polarizations due to addition products are also observed. Using the Den Hollander rule for low magnetic fields we affirmed that the principal radical pair of the photoreaction is formed by the abstraction of a hydrogen atom of the solvent by the nitrogen heterocycles excited in the triplet state. The validity of our results was then confirmed by a study of the photoreduction of acridine in a weak field using the experimental procedures described.