A. Ripamonti

Optical Properties of PPV and PPP Polymers

We present experimental optical absorption and Raman data of PPV and PPP. Theoretical calculations of the band shapes of absorption and Raman spectra of both polymers are reported. In particular the dependence of the Raman band intensities as function of the excitation wavelengths is theoretically accounted for, in very good agreement with experimental data. These features together with the absorption band shapes can be simulated if a distribution of conjugated segments of different lengths is introduced in the calculation.

Interpretation of photoinduced infrared spectra and doping induced Raman scattering in trans-polyacetylene

Abstract We propose an interpretation of the photoinduced infrared spectra of the cis rich (CH) x and fully isomerized trans (CH) x in the framework of the perturbed Green function method in which the lattice dynamics of polyacetylene is considered. The perturbation induced by the photogenerated charge on the lattice is accounted for by a positive parameter Λ which simulates the changes of the force constants due to the modification of the electron-vibration and electron-electron interactions in the excited states with respect to the ground state. By using the same model and by considering a positive change Λ of the force constants, the doping induced Raman modes in n doped trans (CH) x are also well accounted for.

Theoretical analysis of absorption and raman spectra of polyacetyle-type copolymers

Summary form only given. Diblock polyacetylene-polynorbornene copolymers with controlled conjugated sequences have been prepared in both thin films or solution. We report here a theoretical analysis of the absorption and Raman spectra recorded from the different samples in which the conjugated sequences are varied from long to short. In all cases, the same bimodal distribution is used in order to calculate both absorption and Raman spectra whose results are in good agreement with experimental data. In particular, we are able to explain the well resolved structures observed in the spectra from samples in solution characterized by short sequences. The distributions we have used is centered on /spl tilde/ 5 and 10 C = C respectively, with a low weight on the latter one, leading to an overall asymmetric profile. On the other hand, the same analysis applied to the absorption and Raman spectra with long controlled sequences (for example, N/sub C = C/ = 40 or 100), leads to a bimodal distribution centered on 8 and 40 C = C.

Photoinduced Infrared bands in short polyacetylene segments

Abstract We present the theoretical analysis of the photoinduced absorption infrared spectra of Durham type polyacetylene and diblock copolymers. Good agreement with experimental data is found, taking into account the contribution of short segments, in all these samples, expecially in the case of Durham type (CH) x exposed to air. In particular we have well reproduced the different structures of the low frequency absorption band in the photoinduced spectra.

Oriented polyacetylene and copolymer systems: Polarized photoinduced infrared spectra

Abstract We report on the experimental polarized photoinduced infrared absorption spectra of oriented copolymers (CH) x - (polynorbornene) - (CH) x and oriented trans(CH) x . In these experiments the pump beam is polarized perpendicular and the probe beam is polarized parallel to the stretching axis, respectively. In this experiments among the three vibrational photoinduced bands observed in the PIA spectra we focus on the one peaked at 500–600 cm −1 which exhibits a more or less structured shape, sample dependent. Also, changes in the peak position of the low energy electronic band are observed in the different samples. Such a behavior can be interpreted in terms of the perturbation induced by the photogenerated charges on the lattice dynamics of the different conjugated segments. In order to calculate the band shapes, the photoinduced vibrational mode contributions of the different segments are weighted by the conjugation length dependent infrared dipole moments and by the bimodal distribution derived from the Raman spectra analysis of the same samples. Excellent agreement is found between the calculated and the experimentally recorded band shapes in the polarized photoinduced spectra of the different samples. In the framework of this model the changes of the low energy peak position are also qualitatively explained.

Interpretation of the photoinduced absorption spectra of oriented polymer and copolymer systems

Abstract Polarized photoinduced i.r. absorption spectra of stretch-oriented triblock copolymers (CH) x -(polynorbornene) x -(CH) x with different x and n values and of stretch-oriented trans -(CH) x are presented. Sample dependent structured shape of the broad band (maximum at 500–600 cm -1 is observed. This feature is interpretated in the framework of the perturbed Green function method, yielding the determination of the localized photoinduced vibrational modes of the different conjugated segments.

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

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.