Fig. 4
Two-dimensional spectra of MEH-PBI aggregates. The conventional absorptive 2D spectrum occurs near the maximum of the laser spectrum at 16,000 cm−1 (red vertical line labeled as ω) and the EEI2D spectrum near 32,000 cm−1 (red vertical line labeled as 2ω). The spectra are shown for several population times as indicated. Excitation pulse energy was set to 10 nJ. Contours are drawn at fractions of 0.01, 0.03, 0.05, 0.08, 0.13, 0.19, 0.27, 0.4, 0.57, and 0.83 of the maximal signal amplitude. To stress the connection with transient absorption, we employ the same sign convention and plot a decrease of absorption as negative and an increase as positive
