41 research outputs found
Multiscale photosynthetic exciton transfer
Photosynthetic light harvesting provides a natural blueprint for
bioengineered and biomimetic solar energy and light detection technologies.
Recent evidence suggests some individual light harvesting protein complexes
(LHCs) and LHC subunits efficiently transfer excitons towards chemical reaction
centers (RCs) via an interplay between excitonic quantum coherence, resonant
protein vibrations, and thermal decoherence. The role of coherence in vivo is
unclear however, where excitons are transferred through multi-LHC/RC aggregates
over distances typically large compared with intra-LHC scales. Here we assess
the possibility of long-range coherent transfer in a simple chromophore network
with disordered site and transfer coupling energies. Through renormalization we
find that, surprisingly, decoherence is diminished at larger scales, and
long-range coherence is facilitated by chromophoric clustering. Conversely,
static disorder in the site energies grows with length scale, forcing
localization. Our results suggest sustained coherent exciton transfer may be
possible over distances large compared with nearest-neighbour (n-n) chromophore
separations, at physiological temperatures, in a clustered network with small
static disorder. This may support findings suggesting long-range coherence in
algal chloroplasts, and provides a framework for engineering large chromophore
or quantum dot high-temperature exciton transfer networks.Comment: 9 pages, 6 figures. A significantly updated version is now published
online by Nature Physics (2012
Origin of Long Lived Coherences in Light-Harvesting Complexes
A vibronic exciton model is developed to investigate the origin of long lived
coherences in light-harvesting complexes. Using experimentally determined
parameters and uncorrelated site energy fluctuations, the model predicts
oscillations in the nonlinear spectra of the Fenna-Matthews-Olson (FMO) complex
with a dephasing time of 1.3 ps at 77 K. These oscillations correspond to the
coherent superposition of vibronic exciton states with dominant contributions
from vibrational excitations on the same pigment. Purely electronic coherences
are found to decay on a 200 fs timescale.Comment: 4 pages, 2 figure
Role of electronic-vibrational mixing in enhancing vibrational coherences in the ground electronic states of photosynthetic bacterial reaction center.
We describe polarization controlled two-color coherence photon echo studies of the reaction center complex from a purple bacterium Rhodobacter sphaeroides. Long-lived oscillatory signals that persist up to 2 ps are observed in neutral, oxidized, and mutant (lacking the special pair) reaction centers, for both (0°,0°,0°,0°) and (45°,-45°,90°,0°) polarization sequences. We show that the long-lived signals arise via vibronic coupling of the bacteriopheophytin (H) and accessory bacteriochlorophyll (B) pigments that leads to vibrational wavepackets in the B ground electronic state. Fourier analysis of the data suggests that the 685 cm(-1) mode of B may play a key role in the H to B energy transfer