Spectroscopy of transition-metal substituted oligothiophenes

Novel organometallic compounds (suitable for nonlinear optical applications), consisting of oligothiophene substituted Fischer-type carbene complexes, have been studied by using absorption, emission and Raman spectroscopies. 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 excited state, thus accounting for the enhanced second-order nonlinear optical response of this compound. The perturbation on the π conjugated electrons induced by the transition-metal atom is studied and discussed.