Fig. 1. Absorption spectroscopy

Fig. 2. The principle of pump-probe and transient grating spectroscopy

Fig. 3. The principle of two-dimensional spectroscopy

Fig. 4. Two-dimensional spectroscopy probes excitonic structure and energy transfer dynamics in weakly coupled and strongly coupled systems

Fig. 5. Two-dimensional spectroscopy probes electronic and vibrational coherence

Fig. 6. Two-dimensional spectra of chlorophyll a and center-line slope analysis^［46］

Fig. 7. homogeneous and inhomogeneous broadenings of 2D semiconducting materials probed by 2D spectroscopy^［25-26］

Fig. 8. Energy transfer in the FMO complex^［7］

Fig. 9. Charge separation in the heliobacterial reaction center probed by 2D electronic spectroscopy^［19］

Fig. 10. Charge separation and vibrational coherence in P3HT/PCBM nanoparticles