The model for optical properties of PPP-type polymers.

The recently successful model [1, 2] for optical properties of PPV based polymers is applied to the PPP family. More progress is available thanks to analytical results covering not only spectra but also the oscillator strength. We conclude similar assignments and emphasize the delocalized nature of basic features. We demonstrate the existence of different types of Coulomb excitons and their roles in the optical absorption. An important and intriguing difference compared with PPV based polymers is the level inversion for the more strongly localized interband exciton. Comparison is made to available optical and EELS data [3, 4, 5]. Our conclusions are suggestive for the future light — polarized experiments.