A Theoretical Study on the Internal Conversion Dynamics of Chlorophylls

• Main Authors: Petra Shih, 施欣妤
• Other Authors: Yuan-Chung Cheng
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/385g98

碩士 === 國立臺灣大學 === 化學研究所 === 106 === Non-adiabatic transitions in molecular excited states play significant roles in many photophysical and photochemical processes. In particular, the ultrafast internal conversion of Qx→Qy in chlorophylls is crucial to the high efficiency of light harvesting in photosynthesis, yet the mechanism has not been clearly elucidated. In this work, we explored the internal conversion processes of chlorophyll a and bacteriochlorophyll a theoretically by evaluating the vibronic couplings and electronic couplings to construct effective Hamiltonians for the non-adiabatic Qx→Q¬y dynamics. The first principle study of the radiationless relaxation was achieved by combining time dependent density functional theory (TD-DFT) and diabatization method through enforcement of configuration uniformity for the two low lying excited states. The relaxation rates calculated using Fermi’s Golden rule suggest that the sub-100 fs Qx→Qy process can be fully described by a diabatic model with weak vibronic couplings. In addition, we also identified a few key vibrational modes that dominate the Qx→Qy relaxation, and the highly solvent and substituent dependent relaxation rates can be attribute to variations in Qy/Qx energy gaps. The methodology developed is expected to enable detailed dynamical study of energy relaxation in general molecular systems, and it also allows us to gain insights into the natural design of the most important chromophores in photosynthesis.