Fluorescence-Detected Magnetic Field Effects in Exciplex Systems Containing Azacrown Ethers as Electron Donor

Magnetic field effects of radical ion pair reactions detected by exciplex fluorescence spectroscopy were studied in pyrene/aza-15-crown-5 solutions in mixtures of either dimethyl sulfoxide (25 vol %) or acetonitrile (35 vol %) with toluene or benzene at room temperature. It was found that, unlike the extensively studied pyrene/aromatic amine system, the half saturation fields (B 1/2 = 41−52 G, depending on solvents) are almost independent of azacrown concentration. This observation is attributed to the suppression of electron hopping between azacrown molecules and their radical cations. It was also found that sodium ions added to the solutions decrease the magnetic field effect. The results obtained indicate that this cannot be attributed to changes in redox properties of azacrown ethers but might be related to the electron hopping which is facilitated by ligand exchange in the (sodium ion)−(aza-crown ether) complexes.