Endor spectroscopy of poly(paraphenylene vinylene)

Abstract

Summary form only given. Polarons and other elementary excitations in poly(paraphenylene vinylene) (PPV) with nondegenerate ground-state structure have been extensively studied in relation to the mechanism of intense electroluminescence observed in this polymer. The spatial extension, or wave function in other words, of these excitations is an important physical quantity in identifying the existence of the excitations. Recently we have reported the first high-resolution ENDOR (electron nuclear double resonance) spectra of paramagnetic species existing in the dark state of undoped PPV using stretch-oriented samples [1]. The ENDOR spectra exhibit a clear anisotropy of a /spl pi/-electron on the conjugated chain. The maximum value of the spin density reaches 0.09, corresponding to the half-width of the spatial extension of the spin over several phenyl rings. We show that the observed dark spins are trapped polarons from the comparison of dark and photo-induced ESR as well as reported optically-detected ESR (ODESR) spectra. The detail of the spin density distribution will be discussed from the resolved structures in the ENDOR spectrum of the stretch direction.