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Science 8 June 2007:
Vol. 316. no. 5830, pp. 1462 - 1465
DOI: 10.1126/science.1142188
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Reports

Coherence Dynamics in Photosynthesis: Protein Protection of Excitonic Coherence

Hohjai Lee, Yuan-Chung Cheng and Graham R. Fleming*

Department of Chemistry and QB3 Institute, University of California, Berkeley and Physical Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.


Figure 1 Fig. 1. The 2CECPE experiment. (A) The 77 K absorption spectrum (black) of the P-oxidized RC from the photosynthetic purple bacterium R. sphaeroides and the spectral profiles of the ~40-fs laser pulses (blue, 750 nm; red, 800 nm) used in the experiment. (B) The pulse sequence for the 2CECPE experiment. We detect the integrated intensity in the phase-matched direction ks = –k1 + k2 + k3. a.u., arbitrary units. [View Larger Version of this Image (25K GIF file)]
 

Figure 2 Fig. 2. Two-dimensional maps of experimental (A and B) and simulated (C and D) integrated echo signals as a function of the two delay times, t1 and t2, from the RC. The black lines follow the maximum of the echo signal at a given t2. The data at t2 < 75 fs are not shown because the conventional two-color three-pulse photon echo signal (750-750-800 nm) overwhelms the 2CECPE signal in this region, due to the pulse overlap effect. [View Larger Version of this Image (87K GIF file)]
 

Figure 3 Fig. 3. Integrated echo signals as a function of t2 at t1 = 30 fs. Because the system evolves as a coherence between the H and B excitons during the t2 period, this plot represents the dephasing dynamics of the |B > <H| coherence. Measurements at 77 K (A) and 180 K (B) are shown in solid circles, and the theoretical curves are shown in red (c = 0.9) or blue (c = 0.6) lines. a.u., arbitrary units. [View Larger Version of this Image (22K GIF file)]
 

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Science. ISSN 0036-8075 (print), 1095-9203 (online)