Fig. 1. Illustration of 2DES^[6]. (a) Pulse sequence in the 2DES; (b) two-dimensional electronic spectra and its detection information

Fig. 2. A brief history of 2D spectroscopic development^{[5, 22-42]}

Fig. 3. Spectral windows of 2DES (mature techniques are shown inside the dashed box while the developing ones remain outside) (reprinted from Ref. [14], with the permission of AIP Publishing)

Fig. 4. New probing dimensions of 2D spectroscopy. (a) Spatially-resolved fluorescence-detected 2DES^[24]; (b) 2D Stark spectroscopy (reprinted with the permission from Ref. [47], copyright © 2017 American Chemical Society); (c) photocurrent 2DES (reprinted with the permission from Ref. [49], copyright © 2021 American Chemical Society)