Optical excitations in electroluminescent polymers: poly(para-phenylenevinylene) family

TL;DR

This study investigates the nature of optical excitations in electroluminescent polymers, focusing on the size and strength of long-range excitons across different poly(para-phenylenevinylene) family polymers using intermediate exciton theory.

Contribution

It provides a comparative analysis of long-range exciton oscillator strengths and energies in various conjugated polymers, highlighting the influence of molecular structure on excitonic properties.

Findings

Long-range exciton oscillator strengths vary with polymer structure.

Energy position of localized excitons is similar across polymers.

Poly(di-para-phenylenevinylene) exhibits significantly larger oscillator strengths.

Abstract

Component of photoexcited states with large spatial extent is investigated for optical absorption spectra of the electroluminescent conjugated polymers by using the intermediate exciton theory. We calculate the ratio of oscillator strengths due to long-range excitons with respect to sum of all the oscillator strengths of the absorption as a function of the monomer number. The oscillator strengths of the long-range excitons in poly(para-phenylene) are smaller than those in poly(para-phenylenevinylene), and those of poly(para-phenylenedivinylene) are larger than those in poly(para-phenylenevinylene) Such relative variations are explained by the differences of the number of vinylene units. The oscillator strengths of long-range excitons in poly(di-para-phenylenevinylene) are much larger than those of the above three polymers, due to the increase of number of phenyl rings. We also find that the energy position of the almost localized exciton is neary the same in the four polymers.