IAMS/NTU Chem Lecture Announcement
中研院原分所與臺大化學系聯合演講公告
Title: Theoretical Investigation of Exciton Dynamics and Spectroscopy of Natural and Synthetic Light Harvesting Complexes
Speaker: Prof. Seogjoo J. Jang (Department of Chemistry and Biochemistry, Queens College, City University of New York (CUNY) & Chemistry and Physics PhD Programs, Graduate Center, CUNY)
Time: 10:30 AM, March 2 (Thursday), 2023
Place: Dr. Poe Lecture Hall, IAMS (本所浦大邦講堂 臺大校園內)
Contact: Prof. Yuan-Chung Cheng and Dr. Liang-Yan Hsu 鄭原忠教授及許良彥博士
Abstract:
Natural photosynthetic organisms have highly efficient light harvesting complexes, which consist of common pigment molecules such as chlorophylls and bacteriochlorophylls typically embedded in protein scaffolds. These complexes “harvest” photons and convert them into molecular excitons, i.e., spatially delocalized forms of collective excited states created by quantum mechanical superpositions of individual electronic excitations of pigment molecules. Protein environments of natural light harvesting complexes go through significant dynamical fluctuations of multiple timescales and are also subject to various sources of disorder at both molecular and larger length scales. On the other hand, excitons have finite lifetimes of about nanoseconds and their spatial and energetic characteristics depend sensitively on minute details of local chemical and physical environments. Nonetheless, in natural light harvesting complexes, the formation of excitons and their transport over about hundred nanometer length scales occur with almost perfect efficiency until they reach charge transfer areas, where redox reaction cycles for creating chemical sources of energy begin. How nature can create and transport fragile molecular excitons with such high fidelity, despite the presence of significant fluctuations and disorder, has been the subject of decades of spectroscopic and computational studies, but correct mechanistic understanding and quantitative modeling of many of these complexes have become possible only during the past decade. The present talk summarizes our theoretical and computational findings addressing and resolving these issues for the case of light harvesting 2 (LH2) complexes of purple bacteria. It is shown that combinations of new theoretical development, computational modeling, and analyses of spectroscopic data offer not only convincing mechanistic understanding but also semiquantitative description of the exciton dynamics involving single and aggregates of LH2 complexes and their spectroscopic data. These results also provide new insights into how natural light harvesting complexes control negative effects of disorder through interplay of structural factors, hydrogen bonding, and quantum mechanical delocalization of excitons. This talk will also provide an overview of a hierarchy of theories for resonance energy transfer processes and related nonradiative decay processes we have developed, which are more general than seminal but old theories such as Förster’s theory of resonance energy transfer. Model calculations and applications of these theories for organic dye molecules illustrate the importance of theories capturing the right features of molecules and their potential utility for modeling the exciton dynamics in synthetic light harvesting complexes. Unresolved theoretical issues for accurate description of these systems are addressed as well.