Exciton Self Trapping in One-Dimensional Photosynthetic Antennas

Abstract

Experimental evidence is presented showing that excitons in circular antenna complexes from photosynthetic bacteria are dynamically self trapped in about 200 fs by coupling to nuclear vibrations. The induced deformation covers ∼20% of the complex circumference at low temperature. This self trapping, the first of its kind observed in biological systems, results in a broad fluorescence spectrum and considerably improves energy resonance between heterogeneous antenna complexes. Exciton self trapping may thus be a part of nature's strategy, increasing the speed and efficiency of energy transfer in photosynthesis.

Davydov Splitting of Excitons in Cyclic Bacteriochlorophyll a Nanoaggregates of Bacterial Light‐Harvesting Complexes between 4.5 and 263 K

“…The idea of exciton polarons/self-trapped excitons in bacterial LH antennas has been around for at least a decade already. [23,34,49,50,52,53,66,67] Existence of similar quasi-localized excitations in DNA [68] as well as in photosynthetic reaction centers [13] has also been proposed recently. Successful reproduction of most subtle features of the measured spectra demonstrated above is another strong evidence for exciton polarons in the cyclic bacterial antennas.…”

Excitonic polarons in quasi-one-dimensional LH1 and LH2 bacteriochlorophyll a antenna aggregates from photosynthetic bacteria: A wavelength-dependent selective spectroscopy study

“…Contribution of the latter processes into red shift of the fluorescence emission spectrum of LH2 complexes has been established [18]. Subsequent measurements on well-isolated LH2 complexes finally confirmed unusually large from the point of view of Frenkel excitons Stokes shift [19].…”

“…It also appears that the Frenkel exciton model, which includes only static disorder, misses some essential aspects of the reality. A hypothesis was, therefore, raised [19] that excitons in the LH2 and LH1 complexes might be strongly coupled to their dynamic environment, contrary to common notion. In solids the phonons scatter (dephase) the excitons causing homogeneous line broadening [20].…”

Fluctuations in the Electron–Phonon Coupling of a Single Chromoprotein

“…[10,12,13] There are several observations in the emission spectra that are inconsistent with this model, and this suggested a model that considers exciton self-trapping in the B850 assembly. [14][15][16] However, thus far, most of the single-molecule work performed on pigment-protein complexes from purple bacteria has focused on fluorescence-excitation spectroscopy, and the few studies that dealt with single-complex emission spectroscopy did not consider self-trapping processes [17][18][19][20][21] and/or were conducted at room temperature, where all decisive spectral details are completely masked by thermal broadening. [22][23][24][25][26][27][28][29][30] Recently, we addressed this issue by performing fluorescence-excitation and fluorescence spectroscopy on the same individual complex.…”

“…This might explain the inconsistencies that have been observed in absorption and emission studies on ensembles of LH2 concerning the electron-phonon coupling strength. [15] In summary, we have registered emission spectra from individual LH2 complexes from Rps. acidophila at low temperature.…”