Low magnetic field effects on a photoinduced electron transfer reaction in an ionic liquid

[Display omitted] •We observed low magnetic field effects on a bimolecular photoinduced electron transfer reaction in an ionic liquid.•The magnitude of the low magnetic field effect increased as the lifetime of the radical ion pair increased while the position of the low magnetic field effect was unchanged.•The analysis revealed that the simple degenerate model is not sufficient to explain the observed magnetic field effects and suggests that the low magnetic field is caused by other mechanisms such as anti-level crossing and three state mixing. Low Magnetic field effects on a photoinduced electron transfer reaction between benzophenone and 1,4-diazabicyclo [2.2.2] octane (DABCO) in an ionic liquid of N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide were studied with nanosecond transient absorption measurements. At a magnetic field (~2mT) comparable with the hyperfine coupling in DABCO cation, so-called low field effects (LFEs), whose effect is opposite to the magnetic field effects caused by the hyperfine coupling mechanism, were observed on the yield of the benzophenone anion radical. The magnitude of the LFE is linearly increased with the increase of the lifetime of the radical ion pair. The present study provides basic data to clarify the mechanism of LFEs in biological systems.