ELECTRON NUCLEAR DOUBLE RESONANCE SPECTROSCOPY OF SOLITONS AND POLARONS IN CONJUGATED POLYMERS

Abstract

Novel elementary excitations such as solitons and polarons in conjugated polymers carry unpaired electrons. In this case electron nuclear double resonance (ENDOR) of protons on the conjugated chain provides a unique method to observe their wavefunctions. This information has two significant meanings. Firstly, it gives the spatial extension of solitons and polarons, the quantity that is essential in examining the reality of these self-localized excitations. Secondly, it directly probes the degree of electron correlation. In the case of finite electron correlation, negative spin sites appear in the spin-density distribution. The unique and detailed determination of the wavefunctions containing such information can be made only after the careful studies of oriented polymers because of the non-single-crystalline nature of these materials. In this article I review our ENDOR studies on solitons in polyacetylene and polarons in poly(paraphenylene vinylene), performed using stretch-oriented samples. All the analyses are based on the properties of π-electrons which show characteristic anisotropy in oriented samples. The observed spin distributions are compared with theoretical results as well as shown as the basis for further analyses of conjugated polymers.