SPECTROSCOPIC PROPERTIES OF POLYACETYLENE SEGMENTS IN COPOLYMERS

In this paper we present an extensive study of the optical properties of polyacetylene [(CH)(x) and (CD)(x)] segments in copolymers by means of several spectroscopic techniques. They include UV-visible absorpti on, resonant Raman scattering, and photoinduced infrared absorption. A large variety of samples in either diblock or triblock copolymers, in general in the solid state, but also, in one particular case, in solu tion, are investigated. We show that the optical properties of these c opolymers are strongly dependent on the distribution of conjugation le ngths of segments in the different samples. A consistent model based o n the vibrational and electronic properties of the polyacetylene conju gated segments and on a bimodal distribution is used to reproduce the band shapes observed in the UV-visible absorption, resonance Raman sca ttering, and photoinduced infrared-absorption spectra. The calculated structured shapes of the bands, and in particular the features in the low-frequency region of the photoinduced infrared absorption band in t he different samples, are in very good agreement with the experimental data.