Quantum Coherence And Ultrafast Energy Transfer In Photosynthetic Light-harvesting Antennas Using Two-dimensional Electronic Spectroscopy

The high quantum efficiency of photosynthesis in the processes of energy transfer and charge separation has always been attractive to researchers.During the past decade,the proposal of quantum-coherent energy transfer mechanism has opened a door for understanding the primary light-harvesting processes in photosynthetic systems.However,there still exist many debates about how to interpret the physical picture of excitation energy transfer from the observed coherence phenomena.More effective experimental and theoretical methods are needed to verify and distinguish the complicate quantum coherent processes.Based on the advanced experimental tool,twodimensional electronic spectroscopy,this dissertation introduces in detail the main technical difficulties and solutions of this method during instrument construction.We also proposes some optimization schemes in terms of scattering suppression and wedge calibration in experiment.Then,we investigate the ultrafast dynamics and quantum coherence in oxzine 720 dye molecules,higher-plant light-harvesting complex(LHCII)and recombined allophycocyanin(rAPC)step by step according to their complexity of coherence.The vibrational wavepackets on different electronic states in oxazine molecules are distinguished by using the joint method of quantum beating maps and time-frequency analysis.In addition,the multimode-coupled vibrational wavepackets are also identified in oxazine 720.In the spectroscopic studies of LHCII at room temperature,we utilized quantum beating maps to determine its dominant coherent signals resulting from the ground-state vibrational coherence,which has no direct effect on the energy transfer process.In the light-harvesting system rAPC,two-dimensional electronic spectroscopy reveals that both vibrational and vibronic coherences exist under photo-excitation but without strong excition coupling between chromophores.Furthermore,the fact that the dephasing time of coherent signals are consistent with the lifetime of energy transfer strongly suggests an important role of vibronic coherence on the process of energy transfer in rAPC.The experimental observations in this dissertation will be of great significance for understanding the coherent mechanisms of ultrafast energy transfer processes in photosynthetic light-harvesting systems.