Raman study of /spl alpha/-oligothiophenes and model compounds for polythienylene vinylene

Summary form only given. Oligothiophenes have been the subject of intense experimental works recently, due to their potentiality to be used in technical applications. We present here a complete vibrational study of a series of these /spl alpha/-coupled oligothiophenes. Both experimental and theoretical investigations have been carried out by using spectroscopic techniques such as Resonance Raman Scattering (RRS) and infrared absorption and analyzed as a function of the oligorner length. Detailed calculations lead to a clear assignment of the vibrational modes in all compounds and to a determination of the main force constants associated with the different chemical bonds. Also, Raman spectra obtained in p-doped /spl alpha/-6T or p-doped polythiophene are discussed in terms of electronic structure and compared to polyaromatic systems like PPP or PPV. In a similar way, Raman studies of model compounds of PTV, such as trans-bis (2-thienyl)-ethylene (TTE) and a compound made of three thienyl rings and two vinyl groups have been carried out. The two modes associated with the C=C stretching of the vinyl group and the thiophene ring respectively are found to depend on the length of the compounds. All force constants are consistent with those found in other polymers.