Level mixing and energy redistribution in bacterial photosynthetic reaction centers

Journal Article · Thu Mar 28 04:00:00 EST 1996 · Journal of Physical Chemistry

DOI:https://doi.org/10.1021/jp952925k· OSTI ID:226683

Haran, G; Wynne, K; Moser, C C; Dutton, P L; Hochstrasser, R M ^[1]

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1. Univ. of Pennsylvania, Philadelphia, PA (United States)

We performed ultrafast polarized light experiments in which we pumped the 800 nm band and probed several near- and mid-IR transitions of photosynthetic reaction centers from Rhodobacter sphaeroides. Absorption into the upper excitonic level of the special pair (P{sub Y+}) is part of this band, but is not known whether P{sub Y+} behaves as a localized state or if it mixes with accessory bacteriochlorophyll (BChl) states. A calculation of the anisotropy of pump-probe signals fails to reproduce the experimental results if the localized picture is used. In fact, the transition into P{sub Y+} has to be 4-fold intensified over a simple exciton model prediction in order to give rise to anisotropies which are consistent with the experiment. This substantial intensification is consistent with previous experimental results. Agreement between theory and experiment can be achieved if the P{sub Y+} state is mixed with excited states of accessory BChl. Stimulated emission from the lower excitonic level of the special pair (P{sub Y-}), probed at 950 nm after pumping at 800 nm, does not appear instantaneously, but rises with a time constant of 110 fs. A novel excited state absorption of the accessory BChls at 1200 nm, assigned as a monomer transition by comparison with a pump-probe experiment on free BChl dissolved in acetone, also decays with a nearly 100 fs time constant. Although Foerster energy transfer from accessory BChl state to P{sub Y-} can account for the fast transients, under the delocalized state picture suggested in this paper they would rather correspond to an internal conversion process from the mixed states to the P{sub Y-} state. 51 refs., 4 figs., 4 tabs.

• OSTI ID: 226683
• Journal Information: Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 13 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
55 BIOLOGY AND MEDICINE
BASIC STUDIES
66 PHYSICS
ABSORPTION SPECTRA
BACTERIA
CONFIGURATION MIXING
ENERGY LEVELS
ENERGY TRANSFER
EXCITED STATES
INFRARED SPECTRA
PHOTOSYNTHETIC REACTION CENTERS