Large molecular polarizabilities are required for the development of molecular devices to be used in photonics. This goal can be achieved if improved low band gap organic materials become available. For this reason it is of extreme importance to be able to identify the mechanisms which control molecular polarizabilities.
Among the most significant molecular parameters to be used in the choice of a material suitable for molecular electronics, is the extent of intramolecular charge transfer. We have shown that it is possible to obtain an estimate of the intramolecular charge transfer simply using infrared and Raman intensities. This property plays a relevant role also in determining the molecular hyperpolarizabilities. Once again we have shown that vibrational spectra can be used in order to evaluate the vibrational contribution to hyperpolarizabilities.
The values obtained are very large and correlate well with the electronic quantities. This means that the understanding of the vibrational spectra (both in intensity and frequency) can help in the design of new materials. We present experimental and theoretical data that show how this can be done.