Vibrational Raman Spectroscopy of Polyconjugated Organic Oligomers and Polymers

New classes of polymers and oligomers whose backbone consists of a network of delocalized pi electrons have recently been synthesized and show electrical and non-linear optical properties of great interest for new technologies. The vibrational spectra of these materials show peculiar features which, if properly interpreted, can provide unique structural information. The interpretation of the spectra requires the development of new theoretical tools. The theoretical and experimental aspects of the problem are presented. It is also shown that the nuclear relaxation following the excitation of the electrons by an intense electromagnetic field can be described in terms of the vibrational modes and can be related to the nuclear contributions to the non-linear optical responses of the material. In this case Raman intensities play a determining role.