A three essential states model for electroabsorption in nonluminescent π-conjugated polymers

Electroabsorption (EA) spectra of a variety of soluble nonluminescent π-conjugated polymers were measured and analyzed. We modeled the EA spectra using a summation over states model for optical non linearities with three essential states, namely 1Ag, 1Bu and mAg; these are the same states which determine the EA of luminescent conjugated polymers. The model also includes relatively strong phonon interactions and a conjugation length distribution. We have not found substantial contribution to the EA spectra from either the continuum band or from the 2Ag state, even though the relation E(2Ag) < E(1Bu) holds for our films. The EA spectrum of trans-(CH)X has been fit using a bimodal conjugation length distribution consistent with resonant Raman scattering analysis.