MAGNETIC-FIELD EFFECT ON EXCIPLEX LUMINESCENCE IN LIQUIDS

The effect of a magnetic field on the luminescence of unlinked as well as linked exciplex systems has been discussed. The magnetic field modulated luminescence, (DELTAphi/phi ) is not only dictated by the hyperfine interaction in the radical ion pair, but also by the environment , such as viscosity and dielectric constant (c) of the medium and presence of other molecules in the neighbourhood of the exciplex. A complex interplay between spin evolution, radical pair recombination and diffusion determine the magnitude and nature of the magnetic field effect (MFE). The dependence of (DELTAphi/phi) on epsilon could be explained on the basis of simple theoretical models. The concept of Heisenberg spin exchange has been invoked to rationalise the quenching of MFE by lanthanide ions. Time-resolved studies provide useful information regarding the dynamics of the spin-evolution of the system . In viscous medium, the rotational diffusion slows down and the MFE becomes dependent on the direction of the field with respect to the exciplex.