Magnetic field effect on exciplex luminescence in liquids

Abstract

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. (Δφ/φ) is not only dictated by the hyperfine interaction in the radical ion pair, but also by the environment, such as viscosity and dielectric constant (ϵ) 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 (Δφ/φ) on the ϵ 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.