APPROXIMATE DESCRIPTION OF STOKES SHIFTS IN ICT FLUORESCENCE EMISSION

The time-resolved emission spectrum of a dual fluorescent prototype sy stem like DMABN is associated with an intramolecular adiabatic charge- transfer reaction and the simultaneous relaxation of the polarization coordinate describing the dynamic behaviour of the polar solvent. The dynamic Stokes shift of the frequency maximum of the long-wavelength e mission band related to the charge-transfer (CT) state towards the red region is interpreted as a consequence of a kinetic pathway which dev iates from steepest descent to the CT state, the rate-determining step being the solvent relaxation. The present stochastic treatment is bas ed on the assumption that internal and solvent coordinates could be de scribed separately, neglecting coupling elements in the case of slow s olvent relaxation.