Two-Dimensional Electronic Spectroscopy
Two-dimensional electronic spectroscopy (2DES) correlates excitation and emission energies as a function of a delay time between excitation and emission events, within the bandwidth of the laser pulse. 2D spectra are plotted as a function of absorption and emission, and cross-peaks appear where the two frequencies are different, indicating electronic coupling between chromophores and energy transfer. This allows us to monitor the energy flow and find the energy transfer timescales. Recent development of two-color two-dimensional electronic spectroscopy enables us to study energy transfer between pigments well separated in energy, more than the bandwidth of the laser pulse.
Independent control over the polarization of the four beams in 2D spectroscopy allows us to measure the angle between transition dipole moments, thus providing a sensitive measure of the nature and the geometry of the excited states. Polarization-dependent 2D spectroscopy is also important for decongesting crowded 2D spectra, by selectively enhancing and suppressing cross-peaks signals corresponding to different pathways of energy flow.
Two dimensional electronic spectroscopy has recently been successfully applied to the study of the energy landscape of the antenna complex LHCII, the minor complex CP29, involved in both light harvesting and NPQ (non photochemical quenching), and to the bacterial reaction center.
Helpful Background Reading:
Phase-stabilized two-dimensional electronic spectroscopy, T. Brixner, T. Mancal, I. V. Stiopkin, and G. R. Fleming, J. Chem. Phys., 121, 4221-36 (2004).
Ultrafast Multidimensional Spectroscopy: Principles and Applications to Photosynthetic Systems, G. S. Schlau-Cohen, J. M. Dawlaty, G. R. Fleming, IEEE J. Sel. Top. Quant., 99, (2011).
Two-dimensional Electronic Spectroscopy and Photosynthesis: Fundamentals and Applications to Photosynthetic Light-Harvesting, G. S. Schlau-Cohen, A. Ishizaki, G. R. Fleming, Chem. Phys., 1-22 (2011).