Sub-picosecond fluorescence dynamics of organic light-emitting diode tris(8-hydroxyquinoline) metal complexes

For a few complexes belonging to a new class of organic Light-emitting diodes (OLED), namely Al(III)- and Ga(III)-tris-8-hydroxyquinoline (Alq(3) and Gaq(3)), femtosecond fluorescence up-conversion measurements are reported. The fluorescence decays contain picosecond components when the complexes are dissolved in liquid solution. The fast components are not found in the time-resolved fluorescence of the complexes doped in an inert host crystal. The results in liquid solution are characteristic of a dynamic Stokes shift due to the solvation in a Ligand-localized excited state. Furthermore, from the temporal behavior of the total fluorescence intensity it is concluded that, concomitant with solvation, adiabatic electron transfer takes place. (C) 1999 Elsevier Science B.V. All rights reserved.