Control of ferromagnetic and antiferromagnetic couplings in a galvinoxyl–triplet chrysene encounter complex through solvent polarity

Energy difference, J, between the quartet and doublet spin states of a galvinoxyl radical–triplet chrysene pair as an encounter complex in solution was investigated by measuring chemically induced dynamic electron polarization (CIDEP) of galvinoxyl with a time-resolved ESR (TR-ESR) method. All the TR-ESR spectra of galvinoxyl show net type CIDEP signals due to doublet–triplet magnetic interactions. The CIDEP phase switches from absorption in non-polar solvent to emission in polar solvent. The signals were analyzed on the basis of the radical–triplet pair mechanism (RTPM) for CIDEP creation, the results of which indicate that galvinoxyl–triplet chrysene pairs show ferromagnetic and antiferromagnetic couplings in non-polar and polar solvents, respectively. This solvent polarity-controlled switching of magnetic coupling in the galvinoxyl–triplet chrysene pair was interpreted by introducing the effect of intermolecular charge transfer interaction on the J value.