Abstract
High-spectral-resolution hole-burning and fluorescence line-narrowing spectra of excitons in LH2 complexes from the photosynthetic purple bacterium Rhodobacter sphaeroides have been investigated together with conventional broadband fluorescence spectra and their temperature dependence. The steady-state spectroscopy has been complemented by fluorescence lifetime measurements. The experimental results are discussed on the basis of the adiabatic Holstein exciton polaron model, modified by including diagonal disorder. As a result, a new interpretation for the LH2 antenna optical spectra is provided. The exciton when optically excited becomes localized after relaxation. The LH2 fluorescence is mainly due to self-trapped excitons not only at low temperature, as previously suggested (Timpmann, K.; Katiliene, Z.; Woodbury, N. W.; Freiberg, A. J. Phys. Chem. B 2001, 105, 12223), but also over the whole temperature range up to physiological temperatures because the self-trapped exciton binding energy is of the same order as the thermal excitation energy at ambient temperature. The conclusion is made that direct self-trapping relaxation dominates the common energy relaxation between exciton states and that the main factor limiting the relaxed exciton size is dynamic rather than static disorder. The coexistence of large and small exciton polarons at low temperatures has been confirmed. Exciton self-trapping also essentially modifies the long-wavelength tail of the absorption spectrum of LH2 complexes. The fraction of the absorption spectrum that is subject to hole burning is due to large-radius self-trapped excitons that are weakly coupled to the lattice. The rest of this spectrum that survives hole burning belongs to the strongly coupled self-trapped excitons/excimers. Implications of these results on the interpretation of Stark spectroscopy experiments as well as on photosynthetic energy transfer and trapping are discussed.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 11510-11519 |
| Number of pages | 10 |
| Journal | Journal of Physical Chemistry B |
| Volume | 107 |
| Issue number | 41 |
| State | Published - Oct 16 2003 |
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Self-trapped excitons in LH2 antenna complexes between 5 K and ambient temperature. / Freiberg, Arvi; Rätsep, Margus; Timpmann, Kõu; Trinkunas, Gediminas; Woodbury, Neal.
In: Journal of Physical Chemistry B, Vol. 107, No. 41, 16.10.2003, p. 11510-11519.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Self-trapped excitons in LH2 antenna complexes between 5 K and ambient temperature
AU - Freiberg, Arvi
AU - Rätsep, Margus
AU - Timpmann, Kõu
AU - Trinkunas, Gediminas
AU - Woodbury, Neal
PY - 2003/10/16
Y1 - 2003/10/16
N2 - High-spectral-resolution hole-burning and fluorescence line-narrowing spectra of excitons in LH2 complexes from the photosynthetic purple bacterium Rhodobacter sphaeroides have been investigated together with conventional broadband fluorescence spectra and their temperature dependence. The steady-state spectroscopy has been complemented by fluorescence lifetime measurements. The experimental results are discussed on the basis of the adiabatic Holstein exciton polaron model, modified by including diagonal disorder. As a result, a new interpretation for the LH2 antenna optical spectra is provided. The exciton when optically excited becomes localized after relaxation. The LH2 fluorescence is mainly due to self-trapped excitons not only at low temperature, as previously suggested (Timpmann, K.; Katiliene, Z.; Woodbury, N. W.; Freiberg, A. J. Phys. Chem. B 2001, 105, 12223), but also over the whole temperature range up to physiological temperatures because the self-trapped exciton binding energy is of the same order as the thermal excitation energy at ambient temperature. The conclusion is made that direct self-trapping relaxation dominates the common energy relaxation between exciton states and that the main factor limiting the relaxed exciton size is dynamic rather than static disorder. The coexistence of large and small exciton polarons at low temperatures has been confirmed. Exciton self-trapping also essentially modifies the long-wavelength tail of the absorption spectrum of LH2 complexes. The fraction of the absorption spectrum that is subject to hole burning is due to large-radius self-trapped excitons that are weakly coupled to the lattice. The rest of this spectrum that survives hole burning belongs to the strongly coupled self-trapped excitons/excimers. Implications of these results on the interpretation of Stark spectroscopy experiments as well as on photosynthetic energy transfer and trapping are discussed.
AB - High-spectral-resolution hole-burning and fluorescence line-narrowing spectra of excitons in LH2 complexes from the photosynthetic purple bacterium Rhodobacter sphaeroides have been investigated together with conventional broadband fluorescence spectra and their temperature dependence. The steady-state spectroscopy has been complemented by fluorescence lifetime measurements. The experimental results are discussed on the basis of the adiabatic Holstein exciton polaron model, modified by including diagonal disorder. As a result, a new interpretation for the LH2 antenna optical spectra is provided. The exciton when optically excited becomes localized after relaxation. The LH2 fluorescence is mainly due to self-trapped excitons not only at low temperature, as previously suggested (Timpmann, K.; Katiliene, Z.; Woodbury, N. W.; Freiberg, A. J. Phys. Chem. B 2001, 105, 12223), but also over the whole temperature range up to physiological temperatures because the self-trapped exciton binding energy is of the same order as the thermal excitation energy at ambient temperature. The conclusion is made that direct self-trapping relaxation dominates the common energy relaxation between exciton states and that the main factor limiting the relaxed exciton size is dynamic rather than static disorder. The coexistence of large and small exciton polarons at low temperatures has been confirmed. Exciton self-trapping also essentially modifies the long-wavelength tail of the absorption spectrum of LH2 complexes. The fraction of the absorption spectrum that is subject to hole burning is due to large-radius self-trapped excitons that are weakly coupled to the lattice. The rest of this spectrum that survives hole burning belongs to the strongly coupled self-trapped excitons/excimers. Implications of these results on the interpretation of Stark spectroscopy experiments as well as on photosynthetic energy transfer and trapping are discussed.
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M3 - Article
AN - SCOPUS:0242270645
VL - 107
SP - 11510
EP - 11519
JO - Journal of Physical Chemistry B Materials
JF - Journal of Physical Chemistry B Materials
SN - 1520-6106
IS - 41
ER -