Electroabsorption studies of PPV and MEH-PPV

We report the results of an electroabsorption (EA) spectroscopy study of the electronic structure of the conjugated polymer PPV and its soluble derivative MEH-PPV. We find that the EA response of bath polymers is dominated by a Stark shift of the 1Bu exciton. Comparison of the EA spectrum with the Third Harmonic Generation (THG) and two-photon fluorescence spectra for PPV allows us to address the question of the exciton binding energy in these materials. We estimate the binding energy to be 0.8(+/-0.15) eV for PPV and 0.7(+/-0.15) eV for MEH-PPV. We discuss the difference between the optically determined binding energy and that estimated via indirect electrical methods. We also present data for the EA response of higher lying transitions and discuss these in terms of current theoretical models. (C) 1998 Elsevier Science B.V.