Electron-Nuclear Double Resonance Studies of π-Electron Defect States in Undoped Poly (Paraphenylene Vinylene)

Abstract

Electron nuclear double resonance (ENDOR) measurements of paramagnetic species existing in the dark state of undoped poly (paraphenylene vinylene) have been performed using stretch-oriented samples. The spectra have shown a clear anisotropy of a π-electron on the conjugated chain. The maximum value of the spin density reaches 0.09, which corresponds to the half-width of the spatial extension of the spin over several phenyl rings. Three distinct spectral turning points have been resolved for the spectra of stretch direction, showing that the variation of the spin density is not monotonic. The resemblance between the ENDOR-induced ESR spectra and the photo-induced ESR spectra at low temperatures strongly suggests that the observed spins are trapped polarons.