SPECTROSCOPY OF TRANSITION-METAL SUBSTITUTED OLIGOTHIOPHENES

Novel organometallic compounds (suitable for nonlinear optical applica tions), consisting of oligothiophene substituted Fischer-type carbene complexes, have been studied by using absorption, emission and Raman s pectroscopies. The nature of the low-lying charge transfer transition is investigated. It is established that the electrical dipole reverses its direction upon photoexcitation from the ground to the first excit ed state, thus accounting for the enhanced second-order nonlinear opti cal response of this compound. The perturbation on the pi conjugated e lectrons induced by the transition-metal atom is studied and discussed . (C) 1998 Elsevier Science S.A.