Excitation−Emission Polarization Spectroscopy of Single Light Harvesting Complexes
Ivan Scheblykin2011, The Journal of Physical Chemistry B
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Abstract
We thank Oleg Mirzov, Daniel Thomsson, Hongzhen Lin, and Yuxi Tian for valuable discussions. We thank David Adolph and nmC@LU for technical help with film thickness measurements.
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Quantum Coherent Energy Transfer over Varying Pathways in Single Light-Harvesting Complexes
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Single light-harvesting complexes LH-2 from Rhodopseudomonas acidophila were immobilized on various charged surfaces under physiological conditions. Polarized light experiments showed that the complexes were situated on the surface as nearly upright cylinders. Their f luorescence lifetimes and photobleaching properties were obtained by using a confocal f luorescence microscope with picosecond time resolution. Initially all molecules f luoresced with a lifetime of 1 ؎ 0.2 ns, similar to the bulk value. The photobleaching of one bacteriochlorophyll molecule from the 18member assembly caused the f luorescence to switch off completely, because of trapping of the mobile excitations by energy transfer. This process was linear in light intensity. On continued irradiation the f luorescence often reappeared, but all molecules did not show the same behavior. Some LH-2 complexes displayed a variation of their quantum yields that was attributed to photoinduced confinement of the excited states and thereby a diminution of the superradiance. Others showed much shorter lifetimes caused by excitation energy traps that are only Ϸ3% efficient. On repeated excitation some molecules entered a noisy state where the f luorescence switched on and off with a correlation time of Ϸ0.1 s. About 490 molecules were examined.
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