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Modelling exciton dynamics in light-harvesting molecules Ruocco, Leonard
Abstract
I investigate the dynamics of multi-state central systems coupled bilinearly to an external oscillator bath within the noninteracting-blip approximation. I focus on both a 3-site configuration, as well as a 2-site model for the central systems of interest. The 2-site model, dubbed the dual-coupling spin-boson (DCSB) model, includes both diagonal and non-diagonal system-bath couplings, whereas the 3-site model considers only diagonal couplings. The bath spectral densities considered in this work include both Ohmic and super-Ohmic forms, as well as single optical phonon peaks. This work is motivated by the recent observance of long-lived quantum coherence effects in the photosynthetic organism known as the Fenna-Matthews-Olson (FMO) complex. The models investigated in this thesis are applied to this system in an attempt to explain its remarkably efficient exciton transfer mechanism, as well as to shed light on the functionality of coherence. The DCSB model is shown to reproduce the rapid exciton transfer times as well as the relatively long coherence times observed in the FMO complex. The non-diagonal system-bath coupling is shown to play a crucial role in this process. This can be attributed to the inelastic phonon-assisted tunnelling (IPAT) mechanism arising from the presence of significant non-diagonal system-bath interactions. Conversely, the 3-site model predicts rapid but incoherent exciton transfer. This can be attributed to the presence of a resonant state in the 3-site architecture, resulting in a relatively slow exciton transfer mode in the system. Therefore efficient exciton transfer requires a careful configuration of the chromophore energy landscape to avoid a resonant 3-site-V configuration. Furthermore, I conclude that coherence effects arising from excitons delocalised across multiple chromophores, promotes IPAT processes arising from non-diagonal system-bath couplings, producing rapid exciton transfer between chromophores. This offers a potential explanation as to the functional role that coherence plays in the energy transfer mechanism of photosynthesis.
Item Metadata
Title |
Modelling exciton dynamics in light-harvesting molecules
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2019
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Description |
I investigate the dynamics of multi-state central systems coupled bilinearly to an external
oscillator bath within the noninteracting-blip approximation. I focus on both a 3-site
configuration, as well as a 2-site model for the central systems of interest. The 2-site
model, dubbed the dual-coupling spin-boson (DCSB) model, includes both diagonal and
non-diagonal system-bath couplings, whereas the 3-site model considers only diagonal
couplings. The bath spectral densities considered in this work include both Ohmic and
super-Ohmic forms, as well as single optical phonon peaks. This work is motivated by the
recent observance of long-lived quantum coherence effects in the photosynthetic organism
known as the Fenna-Matthews-Olson (FMO) complex. The models investigated in this
thesis are applied to this system in an attempt to explain its remarkably efficient exciton
transfer mechanism, as well as to shed light on the functionality of coherence. The DCSB
model is shown to reproduce the rapid exciton transfer times as well as the relatively long
coherence times observed in the FMO complex. The non-diagonal system-bath coupling
is shown to play a crucial role in this process. This can be attributed to the inelastic
phonon-assisted tunnelling (IPAT) mechanism arising from the presence of significant
non-diagonal system-bath interactions. Conversely, the 3-site model predicts rapid but
incoherent exciton transfer. This can be attributed to the presence of a resonant state in
the 3-site architecture, resulting in a relatively slow exciton transfer mode in the system.
Therefore efficient exciton transfer requires a careful configuration of the chromophore
energy landscape to avoid a resonant 3-site-V configuration. Furthermore, I conclude
that coherence effects arising from excitons delocalised across multiple chromophores,
promotes IPAT processes arising from non-diagonal system-bath couplings, producing
rapid exciton transfer between chromophores. This offers a potential explanation as to the
functional role that coherence plays in the energy transfer mechanism of photosynthesis.
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Genre | |
Type | |
Language |
eng
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Date Available |
2020-02-28
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Provider |
Vancouver : University of British Columbia Library
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Rights |
Attribution-NonCommercial-NoDerivatives 4.0 International
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DOI |
10.14288/1.0376448
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2019-05
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Campus | |
Scholarly Level |
Graduate
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Rights URI | |
Aggregated Source Repository |
DSpace
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Rights
Attribution-NonCommercial-NoDerivatives 4.0 International