The Applications Of Two-dimensional Electronic Spectroscopy In Photosynthetic Light-harvesting Systems

Researchers has long been attracted by the high quantum efficiency energy transfer in the photosynthesis.The emergence of two-dimensional electronic spectroscopy(2DES)technology has greatly promoted people's understanding of its mechanism.This thesis systematically introduces the theoretical and experimental techniques of 2DES.For the theoretical part,we derive the two theoretical frameworks of 2DES,one is the optical re-sponse function(ORF),the other one is the equation-of-motion phase-matching approach(EOM-PMA).For the experimental part,we introduce the spectroscopy signal acquisi-tion and experimental data processing in detail.We combine the hierarchical equations of motion method and EOM-PMA referred as HEOM-PMA to calculate 2DES of model dimer systems.When the laser pulse is short enough,the HEOM-PMA reproduces the results based on 3rd ORFs calculations in the impulsive limit.Finite laser pulse width is found to affect both the peak positions and shapes,as well as the time evolution of diagonal and cross peaks.Simulations of the two-color 2DES also show that,to observe quantum beats in the diagonal and cross peaks,it is necessary to excite the related exci-tonic states simultaneously.Then,we simulate the 2DES of the light-harvesting complex II(LHCII)at room temperature.The laser-excited population dynamics of LHCII is also calculated to help understanding the 2DES.Three different excitation schemes are studied,including(1)only the chlorophyll(Chl)b states of LHCII are excited,(2)only the Chl a states are excited,and(3)both the Chl b and Chl a states are excited.The energy transfer pathways and time scales revealed from the 2DES in schemes(1)and(2)agree with the recent experimental studies for the Chl b to Chl a energy transfer and the excitation energy relaxation process within the Chl a manifold.We also propose a dif-ferent way to better present the signals of bottleneck states by investigating the diagonal peaks of the 2DES in scheme(3).