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. (C) 2003 Elsevier Science B.V. All rights reserved.