Vibrational spectroscopy of polyconjugated systems and molecular nonlinearoptical responses

The purpose of this work is to illustrate a new use that can be made of vib rational spectroscopy. It will be shown how it is possible from the knowled ge of vibrational absolute intensities (infrared, Raman and hyperRaman) to obtain the vibrational contribution to nonlinear optical responses. This co ntribution, in the case of polyconjugated systems, is very large (of the sa me order of magnitude or even larger than the electronic one) and, in many instances, it correlates well with its electronic counterpart. Moreover, ne w criteria to relate intensity patterns to molecular structure of polyconju gated systems are discussed. (C) 2000 Elsevier Science B.V. All rights rese rved.