Fig. 2. Measured two-dimensional electronic spectra for the four copolymers in toluene solution at population time T = 991 fs. We distinguish the conventional absorptive 2D (blue rectangle) and fifth-order EEI2D (red rectangle) spectra arising around the fundamental pump wavenumber or its double, respectively (red dashed lines). The rectangles indicate regions of interest for calculating integrated signals that are further analyzed as a function of the population time.