Advanced

Excited States of Carotenoids and Their Functions in Light Harvesting

Zigmantas, Donatas LU (2002)
Abstract
The research presented in this thesis is focused on characterization of photophysical properties of lowest singlet excited states of carotenoids and their functions in the process of photosynthetic light harvesting. It is shown that the various light-harvesting complexes utilize different strategies to achieve efficient energy transfer from carotenoids to (bacterio)chlorophylls. Any study of energy transfer processes in carotenoids is complicated by the fact that the lowest excited singlet state (S1) is a dark state. To overcome this problem, we have developed a technique for direct determination of the S1 state energy, by employing near-IR pump-probe transient absorption spectroscopy to measure the allowed S1 - S2 transition. Using this... (More)
The research presented in this thesis is focused on characterization of photophysical properties of lowest singlet excited states of carotenoids and their functions in the process of photosynthetic light harvesting. It is shown that the various light-harvesting complexes utilize different strategies to achieve efficient energy transfer from carotenoids to (bacterio)chlorophylls. Any study of energy transfer processes in carotenoids is complicated by the fact that the lowest excited singlet state (S1) is a dark state. To overcome this problem, we have developed a technique for direct determination of the S1 state energy, by employing near-IR pump-probe transient absorption spectroscopy to measure the allowed S1 - S2 transition. Using this technique we have successfully determined the S1 energy of a number of biologically active carotenoids. Spectroscopic and dynamical properties of excited states of the carotenoids spheroidene and peridinin were studied in detail. For spheroidene in solution, it was shown that different S1 state conformations can coexist, which results in a measurement-dependent discrepancy in the S1 state energy estimates. Properties of the lowest singlet excited states of the highly substituted carotenoid peridinin proved to be very different from other carotenoids. Studies of peridinin in different solvents revealed a strong lifetime dependence on solvent polarity, suggesting the presence of an intermolecular charge transfer (ICT) state in the excited state manifold. We have discovered a specific probe to study the ICT state dynamics, as the ICT state is characterized by a strong emission band in the near-infrared region centered at 950 nm. The dependence of peridinin excited state dynamics on excitation wavelength, viscosity and temperature was also investigated and incorporated into a new model of the kinetics and energy levels. Data obtained from the carotenoid studies in solution was applied to investigations of the role of singlet excited states of carotenoids in light-harvesting complexes. For the peridinin-chlorophyll-a-protein (PCP) complex it was shown that all singlet excitedstates of peridinin including the ICT state are involved in energy transfer from carotenoid to chlorophyll-a molecules. Furthermore, we have demonstrated that the efficiency of the energy transfer from the S1 state of carotenoids in LH2 complexes in photosynthetic bacteria is directly related to the energy of the S1 state. Finally, we have shown that it is changes in protein conformation induced by specific binding of carotenoids rather than their individual photochemical properties that are involved in energy quenching processes in plant light-harvesting complexes. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof Fleming, Graham R., Department of Chemistry, University of California, and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA, fax.: 1 510 642 6340
organization
publishing date
type
Thesis
publication status
published
subject
keywords
spektroskopi, magnetic and optical properties, Carotenoids, light-harvesting, excited states, excitation energy transfer, femtosecond spectroscopy, supraconductors, magnetic resonance, electrical, Condensed matter:electronic structure, time-resolved fluorescence spectroscopy, magnetisk resonans, supraledare, magnetiska och optiska), egenskaper (elektriska, Kondenserade materiens egenskaper:elektronstruktur, relaxation, spectroscopy
pages
208 pages
publisher
Donatas Zigmantas, Dep. of Chemical Physics, Chemical Center, P.O. Box 124, Lund University
defense location
Chemical Center, hall C
defense date
2002-11-22 10:15
ISBN
91-628-5455-0
language
English
LU publication?
yes
id
ae92bd40-04a7-49df-bccc-3509eb9be642 (old id 465117)
date added to LUP
2007-10-14 16:26:19
date last changed
2016-09-19 08:45:10
@misc{ae92bd40-04a7-49df-bccc-3509eb9be642,
  abstract     = {The research presented in this thesis is focused on characterization of photophysical properties of lowest singlet excited states of carotenoids and their functions in the process of photosynthetic light harvesting. It is shown that the various light-harvesting complexes utilize different strategies to achieve efficient energy transfer from carotenoids to (bacterio)chlorophylls. Any study of energy transfer processes in carotenoids is complicated by the fact that the lowest excited singlet state (S1) is a dark state. To overcome this problem, we have developed a technique for direct determination of the S1 state energy, by employing near-IR pump-probe transient absorption spectroscopy to measure the allowed S1 - S2 transition. Using this technique we have successfully determined the S1 energy of a number of biologically active carotenoids. Spectroscopic and dynamical properties of excited states of the carotenoids spheroidene and peridinin were studied in detail. For spheroidene in solution, it was shown that different S1 state conformations can coexist, which results in a measurement-dependent discrepancy in the S1 state energy estimates. Properties of the lowest singlet excited states of the highly substituted carotenoid peridinin proved to be very different from other carotenoids. Studies of peridinin in different solvents revealed a strong lifetime dependence on solvent polarity, suggesting the presence of an intermolecular charge transfer (ICT) state in the excited state manifold. We have discovered a specific probe to study the ICT state dynamics, as the ICT state is characterized by a strong emission band in the near-infrared region centered at 950 nm. The dependence of peridinin excited state dynamics on excitation wavelength, viscosity and temperature was also investigated and incorporated into a new model of the kinetics and energy levels. Data obtained from the carotenoid studies in solution was applied to investigations of the role of singlet excited states of carotenoids in light-harvesting complexes. For the peridinin-chlorophyll-a-protein (PCP) complex it was shown that all singlet excitedstates of peridinin including the ICT state are involved in energy transfer from carotenoid to chlorophyll-a molecules. Furthermore, we have demonstrated that the efficiency of the energy transfer from the S1 state of carotenoids in LH2 complexes in photosynthetic bacteria is directly related to the energy of the S1 state. Finally, we have shown that it is changes in protein conformation induced by specific binding of carotenoids rather than their individual photochemical properties that are involved in energy quenching processes in plant light-harvesting complexes.},
  author       = {Zigmantas, Donatas},
  isbn         = {91-628-5455-0},
  keyword      = {spektroskopi,magnetic and optical properties,Carotenoids,light-harvesting,excited states,excitation energy transfer,femtosecond spectroscopy,supraconductors,magnetic resonance,electrical,Condensed matter:electronic structure,time-resolved fluorescence spectroscopy,magnetisk resonans,supraledare,magnetiska och optiska),egenskaper (elektriska,Kondenserade materiens egenskaper:elektronstruktur,relaxation,spectroscopy},
  language     = {eng},
  pages        = {208},
  publisher    = {ARRAY(0x93f2550)},
  title        = {Excited States of Carotenoids and Their Functions in Light Harvesting},
  year         = {2002},
}