ENDOR spectroscopy of poly(paraphenylene vinylene)

Electron nuclear double resonance (ENDOR) measurements have been performed on stretch-oriented undoped poly(paraphenylene vinylene) at 4K. Spectra show clear anisotropy of unpaired 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. Spectrum of the stretch direction is associated with resolved structures, showing that the spin distribution is not monotomic. Resemblance between the dark ESR, detected by ENDOR-induced ESR, with light-induced ESR strongly suggests that the observed spins are trapped polarons.