Electron-nuclear double-resonance spectra of polarons in poly(paraphenylene vinylene)

Electron-nuclear double-resonance (ENDOR) spectra of undoped poly(parapheny lene vinylene) are well described by the spin density distribution of the p olaron for finite electron-electron interactions. Theoretically calculated spin distribution using the Pariser-Parr-Pople model with intermediate stre ngth of the interactions yields the maximum spin density of 0.09 at vinylen e sites with the half-width of the distribution over four PPV monomer units . The non-monotonic form of distribution together with the signs of spin de nsities are confirmed with the ENDOR-induced ESR as well as electron-nuclea r-nuclear triple resonance (TRIPLE). The observed extension of the polaron is larger than that of the soliton reported in polyacetylene, which may be related to the nature of the polaron in conjugated polymers being viewed as a hound soliton pair.