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Ultrafast formation of a carotenoid radical in LH2 antenna complexes of purple bacteria

Polivka, Tomas LU ; Pullerits, Tönu LU ; Frank, H A; Cogdell, R J and Sundström, Villy LU (2004) In The Journal of Physical Chemistry Part B 108(39). p.15398-15407
Abstract
The SI-mediated carotenoid to BChl a energy-transfer pathway and carotenoid radical formation have been studied using femtosecond time-resolved transient absorption spectroscopy. A series of LH2 complexes (LH2 = light-harvesting complex 2) from Rhodobacter sphaeroides incorporating carotenoids neurosporene, spheroidene, and spheroidenone were used to explore the effect of conjugation length. The S, lifetimes of carotenoids in the LH2 complex are significantly shorter than in solution, resulting in efficiencies of the S-1-mediated energy transfer of 94%, 82%, and 76%, respectively. In addition to the S-1 decay, a low-amplitude component of similar to9 ps was revealed for all carotenoids in LH2 and assigned to the S* state. Besides energy... (More)
The SI-mediated carotenoid to BChl a energy-transfer pathway and carotenoid radical formation have been studied using femtosecond time-resolved transient absorption spectroscopy. A series of LH2 complexes (LH2 = light-harvesting complex 2) from Rhodobacter sphaeroides incorporating carotenoids neurosporene, spheroidene, and spheroidenone were used to explore the effect of conjugation length. The S, lifetimes of carotenoids in the LH2 complex are significantly shorter than in solution, resulting in efficiencies of the S-1-mediated energy transfer of 94%, 82%, and 76%, respectively. In addition to the S-1 decay, a low-amplitude component of similar to9 ps was revealed for all carotenoids in LH2 and assigned to the S* state. Besides energy transfer, excitation of the carotenoid S-2 state in LH2 complexes also leads to the formation of a carotenoid radical, and this pathway is also conjugation length dependent. The carotenoid radical is formed as a result of electron transfer between the carotenoid and B800 BChl a molecules. The yield of the radical formation is highest for neurosporene (10-15%), while a lower efficiency was observed for spheroidene (5-8%). For spheroidenone, no distinct radical signal was found, The precursor of the carotenoid radical is a charge-transfer state that is populated directly from the S-2 state. This charge-transfer state, which represents an excited state of the carotenoid-B800 complex, decays in 300 fs (neurosporene) or 400 fs (spheroidene) to form ground-state carotenoid cation and BChl anion. The charge-separated state has a lifetime of 2 ps (neurosporene) and 8 ps (spheroidene). (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
The Journal of Physical Chemistry Part B
volume
108
issue
39
pages
15398 - 15407
publisher
The American Chemical Society
external identifiers
  • wos:000224070200084
  • scopus:3042751986
ISSN
1520-5207
DOI
10.1021/jp0483019
language
English
LU publication?
yes
id
7bc6b811-c9e4-444e-be73-a909d7476674 (old id 138934)
date added to LUP
2007-07-03 14:44:46
date last changed
2017-03-05 04:13:29
@article{7bc6b811-c9e4-444e-be73-a909d7476674,
  abstract     = {The SI-mediated carotenoid to BChl a energy-transfer pathway and carotenoid radical formation have been studied using femtosecond time-resolved transient absorption spectroscopy. A series of LH2 complexes (LH2 = light-harvesting complex 2) from Rhodobacter sphaeroides incorporating carotenoids neurosporene, spheroidene, and spheroidenone were used to explore the effect of conjugation length. The S, lifetimes of carotenoids in the LH2 complex are significantly shorter than in solution, resulting in efficiencies of the S-1-mediated energy transfer of 94%, 82%, and 76%, respectively. In addition to the S-1 decay, a low-amplitude component of similar to9 ps was revealed for all carotenoids in LH2 and assigned to the S* state. Besides energy transfer, excitation of the carotenoid S-2 state in LH2 complexes also leads to the formation of a carotenoid radical, and this pathway is also conjugation length dependent. The carotenoid radical is formed as a result of electron transfer between the carotenoid and B800 BChl a molecules. The yield of the radical formation is highest for neurosporene (10-15%), while a lower efficiency was observed for spheroidene (5-8%). For spheroidenone, no distinct radical signal was found, The precursor of the carotenoid radical is a charge-transfer state that is populated directly from the S-2 state. This charge-transfer state, which represents an excited state of the carotenoid-B800 complex, decays in 300 fs (neurosporene) or 400 fs (spheroidene) to form ground-state carotenoid cation and BChl anion. The charge-separated state has a lifetime of 2 ps (neurosporene) and 8 ps (spheroidene).},
  author       = {Polivka, Tomas and Pullerits, Tönu and Frank, H A and Cogdell, R J and Sundström, Villy},
  issn         = {1520-5207},
  language     = {eng},
  number       = {39},
  pages        = {15398--15407},
  publisher    = {The American Chemical Society},
  series       = {The Journal of Physical Chemistry Part B},
  title        = {Ultrafast formation of a carotenoid radical in LH2 antenna complexes of purple bacteria},
  url          = {http://dx.doi.org/10.1021/jp0483019},
  volume       = {108},
  year         = {2004},
}