Two-Dimensional Electronic Spectroscopy (2DES) belongs to the family of 3rd order nonlinear optical spectroscopic techniques. It can be considered as an “upgrade” of the conventional transient absorption spectroscopy (TAS) experiment by adding an extra dimension in the excitation frequency axis. In a 2D spectrum, correlations are studied between the excitation (pump) frequency with the detection (probe) frequency, as a function of the pump-probe delay or waiting time. I shall briefly introduce the principles behind 2DES, followed by discussing two areas of applications that our research group is pursuing.
Excitation Energy Transfer Processes in Plant Light Harvesting Complex II (LHCII). LHCII is the most abundant membrane protein on the planet. It is responsible for harvesting solar power and transferring the excitation energy to the photosynthetic reaction center of plants. We report on our efforts in mapping out the excitation energy transfer (EET) network of LHCII and understanding various aspects of the EET processes in LHCII.
Ultrafast Spectral Diffusion Dynamics of Chlorophylls and Other Molecular Systems. Special diffusion arises from the fluctuation of the chromophores’ transition frequencies induced by various intra- and inter-molecular dynamics. We use 2DES to measure spectral diffusion dynamics of chlorophyll and other molecules, providing valuable insights into how the molecular systems interact with environmental degrees of freedom, such as vibrational relaxations, solute/solvent interactions.