Pump-probe polarization anisotropy study of femtosecond energy transfer within the photosynthetic reaction center of Rhodobacter sphaeroides R26

Journal Article · Thu Jul 25 04:00:00 EDT 1996 · Journal of Physical Chemistry

DOI:https://doi.org/10.1021/jp960708t· OSTI ID:380798

Jonas, D M; Lang, M J; Nagasawa, Yutaka; Joo, T; Fleming, G R ^[1]

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1. Univ. of Chicago, IL (United States)

The energy transfer from the accessory bacteriochlorophylls (B) to the special pair (P) in the photosynthetic reaction center has been time resolved with pump-probe polarization anisotropy measurements using 20-25 fs duration pulses near 800 nm. The pump excitation corresponds to 1.4 x 10{sup 6} photons/{mu}m{sup 2}: the `saturation intensity` for the charge separation quantum yield is 3 x 10{sup 7} photons/{mu}m{sup 2}. The initial pump-probe anisotropy is 0.4 and decays with a nearly 80 fs time constant, which we attribute to dipole reorientation by electronic energy transfer. Simultaneous kinetic modeling of the parallel, perpendicular, and magic angle pump-probe transients using the reaction center structure and dipole orientations is consistent with energy transfer proceeding in two steps: nearly 80 fs electronic energy transfer from the accessory bacteriochlorophylls to the upper exciton component of the special pair (B {yields} P{sub +}) followed by a nearly 150 fs internal conversion from the upper exciton component to the lower exciton component of the special pair (P{sub +} {yields} P{sub -}). Finally, charge separation after electron transfer from P{sub -} to H causes an electrochromic (Stark) shift of B and produces the 2.8 ps bleach rise. The two-step energy transfer model is supported by the observation of weak quantum beat oscillations (125 cm{sup -1} and 227 cm{sup -1}) with near-zero anisotropy in the pump-probe signals. 86 refs., 13 figs., 4 tabs.

• OSTI ID: 380798
• Journal Information: Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 30 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
40 CHEMISTRY
55 BIOLOGY AND MEDICINE
BASIC STUDIES
ABSORPTION SPECTRA
ANISOTROPY
BACTERIA
CHLOROPHYLL
ELECTRONIC STRUCTURE
ENERGY TRANSFER
EXCITED STATES
GROUND STATES
PHOTOSYNTHESIS
PHOTOSYNTHETIC REACTION CENTERS
PIGMENTS
POLARIZATION