Excitonic Excited States and Optical Spectra in Poly(p-Phenylenevinylene) Prepared by Carefully Controlled Thermal Elimination Reaction

Abstract

Optically excited excitonic states have been studied in poly(p-phenylenevinylene) films carefully prepared by the sulfonium salt method. The conspicuous vibronic structures in the reflection spectrum together with the steep absorption edge indicate that the conjugation length distribution has a smaller standard deviation than that reported by Rauscher et al. The small deviation also manifests itself in the more clearly resolved vibronic structures in the emission spectra. The photocurrent is excited only near the intrinsic absorption edge and its efficiency is very low. The resonance Raman spectrum does not show any multiphonon lines, and its relative intensity with respect to the emission intensity is considerably weak. Two strong Raman lines appear at 0.146 eV (1176 cm^-1) and 0.197 eV (1586 cm^-1), which are very close to the phonon energies in the vibronic spectra of emission and reflection, respectively; the transition process can be regarded as charge transfer between the phenylene and the vinylene groups.