Tracing photoinduced electron transfer process in conjugated polymer/fullerene bulk heterojunctions in real time

Ultrafast spectroscopic studies using an optical excitation of a conjugated polymer by sub-10-fs pulses are reported. Phonon modes which are strongly coupled to the electronic excitation of the conjugated polymer are directly observed as coherent oscillations during the pump-probe experiment, mirror ing the resonant/nonresonant Raman spectrum of the conjugated polymer. In c omposites of a conjugated polymer with a fullerene the primary photoexcitat ion is found to be an ultrafast photoinduced electron transfer. We are able to time resolve for the first time the kinetics of this charge transfer pr ocess with a forward transfer time of around tau (et) similar to 45 fs. (C) 2001 Elsevier Science B.V. All rights reserved.