POLAR MOLECULAR CLUSTERS PRODUCED UPON PHOTOINDUCED ELECTRON-TRANSFER IN AN INTERMOLECULAR EXCIPLEX IN BINARY SOLVENTS

A remarkably large magnetic field effect (MFE) on the fluorescence intensity of an intermolecular pyrene/N,N-dimethylaniline exciplex is observed in binary solvents containing components of considerably different relative permittivities. The values of the MFE, which depend on the composition of the binary solvent mixture, are maximal (18%, B = 30 mT) when the volume fraction of the polar component is approximately 0.26 for a benzene/dimethyl sulfoxide liquid mixture. A simple model is proposed which assigns these features to the production of polar microdomains around each radical-ion pair. Solvent sorting then prevents ion pair dissociation.