Interpretation of the Photoinduced Infrared Spectra of Oriented Polyacetylene and Triblock Copolymers

Abstract

We present new experimental data of IR photoinduced absorption of oriented triblock copolymers (CH)_x-polynorbornene-(CH)x and of oriented trans-(CH)_x. All spectra have been recorded with the pump laser light polarized perpendicular and the probe beam polarized parallel to the stretching axis of the chains. Among, the different photoinduced features, the broad band peaked at ~ 500 – 600 cm^-1 exhibits a structured shape more or less pronounced depending on the sample. To explain these features, we propose an interpretation which is based on the perturbed Green function method leading to the determination of the photoinduced localized vibrational modes. The bimodal distribution of conjugated segments, derived from Raman data, is then used to weigh the vibrational contribution to the photoinduced broad band from the different segments. All experimental data presented here are therefore interpreted with such a model.