ENDOR spectra of polarons in poly(paraphenylene vinylene)

Electron nuclear double resonance (ENDOR) spectra of π-electron spin defects in undoped poly(paraphenylene vinylene), PPV have been measured using stretch-oriented polymers. Detailed spectral line shape observed with the aid of ENDOR-induced ESR technique reveals that the spin density extends over about 4 phenyl rings in half-width and the maximum and the second largest spin densities reside on the carbons of vinylene sites. These features correspond well to those of the theoretically calculated spin density distribution of polarons in the case of finite electron correlation, supporting that the spin defects are trapped polarons, as we proposed previously. The polaron spin distribution also well reproduces the photoinduced ESR spectra of PPV, showing that polarons are photogenerated in this polymer.