To treat the field–matter interaction perturbatively, we modify the method developed by Meier and Tannor [C. Meier, D.J. Tannor, J. Chem. Phys. 111 (1999) 3365] and originally designed for propagation of reduced density matrix of systems interacting with arbitrary laser fields. Our approach is of interest to nonlinear optics. We apply this method to a simulation of transient four-wave mixing experiments for ultrafast photoinduced electron-transfer systems in a condensed phase environment. We show that such measurements are more sensitive to vibrational coherence than the electronic populations monitored in pump–probe experiments.
