Dispersion of Resonant Raman Scattering inπ-Conjugated Polymers: Role of the Even Parity Excitons

Abstract

Resonant Raman scattering dispersion of the most strongly coupled phonon frequencies with the excitation laser photon energy is measured in terms of a dispersion rate parameter $D$ and quantified in a variety of π conjugated polymer films. $D$ was found to be large in nonluminescent polymers and small in luminescent polymers. We show that $D$ is determined by the dependence of the even parity excitons $\left(A_g\right)$ on the polymer conjugation length, and this may serve as a useful spectroscopy for the ${2A}_g$ exciton in nonluminescent polymers where it is otherwise optically inactive.