Multidimensional Fluorescence Polarization Imaging of Single Light Harvesting Complexes

University dissertation from Department of Chemistry, Lund University

Abstract: This thesis presents my research journey in the Department of Chemical Physics,Lund University. Multidimensional fluorescence polarization imaging is used to study single LH2s. The method uses linearly polarized excitation light and the emission is detected through a polarizer. The multidimensionality is achieved by rotating the excitation and detection polarizations which enables the construction of 2-dimensional excitation-emission polarization maps of the fluorescence intensity. The method provides information about the molecular energy level structure and spatial orientation of the molecule. The method is particularly useful for multichromophoric systems like LH2 where it is capable of tracking the energy transfer from an excited chromophore to the emitting one. Simulations based on Redfield relaxation theory,are in good agreement with the experimental data. The simulations include the known structure of LH2, independent spectroscopic information about electron-phonon coupling and energetic disorder. The thesis is organized as a collection of the articles preceded by an overview of the light harvesting antenna system, the experimental technique and the results. Chapter I gives the general introduction to the light harvesting antenna systems and in particular the peripheral light harvesting antenna of purple bacterial, called LH2. The chapter II deals with the technical aspects of single complex multidimensional polarization imaging on LH2. The section also gives a short introduction to the relevant software and data analysis. Chapter III gives an overview of LH2 studies in the field of single molecule spectroscopy and bimolecular nano-technology. Last chapter IV summarizes the experimental results, simulations and main conclusions.

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