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Non-radiative relaxation of photoexcited chlorophylls: theoretical and experimental study.

Bricker WP, Shenai PM, Ghosh A, Liu Z, Enriquez MG, Lambrev PH, Tan HS, Lo CS, Tretiak S, Fernandez-Alberti S, Zhao Y - Sci Rep (2015)

Bottom Line: Nonradiative relaxation of high-energy excited states to the lowest excited state in chlorophylls marks the first step in the process of photosynthesis.Modeling this process with non-adiabatic excited state molecular dynamics simulations uncovers a critical role played by the different side groups in the two molecules in governing the intramolecular redistribution of excited state wavefunction, leading, in turn, to different time-scales.This is achieved via selective participation of specific atomic groups and complex global migration of the wavefunction from the outer to inner ring, which may have important implications for biological light-harvesting function.

View Article: PubMed Central - PubMed

Affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University, Saint Louis, Missouri 63130, USA.

ABSTRACT
Nonradiative relaxation of high-energy excited states to the lowest excited state in chlorophylls marks the first step in the process of photosynthesis. We perform ultrafast transient absorption spectroscopy measurements, that reveal this internal conversion dynamics to be slightly slower in chlorophyll B than in chlorophyll A. Modeling this process with non-adiabatic excited state molecular dynamics simulations uncovers a critical role played by the different side groups in the two molecules in governing the intramolecular redistribution of excited state wavefunction, leading, in turn, to different time-scales. Even given smaller electron-vibrational couplings compared to common organic conjugated chromophores, these molecules are able to efficiently dissipate about 1 eV of electronic energy into heat on the timescale of around 200 fs. This is achieved via selective participation of specific atomic groups and complex global migration of the wavefunction from the outer to inner ring, which may have important implications for biological light-harvesting function.

No MeSH data available.


Related in: MedlinePlus

Schematic of predominant redistribution of the transition density localization during the overall B to Qy conversion for both chlorophyll a and b.
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f8: Schematic of predominant redistribution of the transition density localization during the overall B to Qy conversion for both chlorophyll a and b.

Mentions: Furthermore, we report differences in the transient intramolecular energy redistributions that can take account of the experimental differences in the B → Qx → Qy internal conversion rates. The different substituents between chlorophyll species have been shown to play significant roles during the early times of the electronic energy relaxation that involve B → Qx energy transfer. Despite that, the internal conversion process in both the Chls culminates with the exciton localized mainly on the common “inner carbon macrocycle”. Figure 8 depicts a schematic representation of the overall internal conversion process. It exhibits the evolution of time-dependent electronic wavefunction presenting a complex superposition of adiabatic electronic states across 500 trajectories, which cannot be approximated by a simple analysis of adiabatic states at ground state optimal geometry. It may then be inferred that any potential impact that different side-groups of different chlorophyll species can have on the intermolecular energy transfer processes that participate in the photosynthetic process will depend upon the relative time scales between the intermolecular and intramolecular energy transfer processes. If intermolecular energy transfers are concomitant with the intramolecular internal conversion, the transient localization of the exciton on the O71 atoms can modify the intermolecular process according to the chlorophyll species. Otherwise, if the intermolecular energy transfer is subsequent to it, the transfer from an exciton localized on the inner macrocycle seems to be common to the two types of Chls.


Non-radiative relaxation of photoexcited chlorophylls: theoretical and experimental study.

Bricker WP, Shenai PM, Ghosh A, Liu Z, Enriquez MG, Lambrev PH, Tan HS, Lo CS, Tretiak S, Fernandez-Alberti S, Zhao Y - Sci Rep (2015)

Schematic of predominant redistribution of the transition density localization during the overall B to Qy conversion for both chlorophyll a and b.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561917&req=5

f8: Schematic of predominant redistribution of the transition density localization during the overall B to Qy conversion for both chlorophyll a and b.
Mentions: Furthermore, we report differences in the transient intramolecular energy redistributions that can take account of the experimental differences in the B → Qx → Qy internal conversion rates. The different substituents between chlorophyll species have been shown to play significant roles during the early times of the electronic energy relaxation that involve B → Qx energy transfer. Despite that, the internal conversion process in both the Chls culminates with the exciton localized mainly on the common “inner carbon macrocycle”. Figure 8 depicts a schematic representation of the overall internal conversion process. It exhibits the evolution of time-dependent electronic wavefunction presenting a complex superposition of adiabatic electronic states across 500 trajectories, which cannot be approximated by a simple analysis of adiabatic states at ground state optimal geometry. It may then be inferred that any potential impact that different side-groups of different chlorophyll species can have on the intermolecular energy transfer processes that participate in the photosynthetic process will depend upon the relative time scales between the intermolecular and intramolecular energy transfer processes. If intermolecular energy transfers are concomitant with the intramolecular internal conversion, the transient localization of the exciton on the O71 atoms can modify the intermolecular process according to the chlorophyll species. Otherwise, if the intermolecular energy transfer is subsequent to it, the transfer from an exciton localized on the inner macrocycle seems to be common to the two types of Chls.

Bottom Line: Nonradiative relaxation of high-energy excited states to the lowest excited state in chlorophylls marks the first step in the process of photosynthesis.Modeling this process with non-adiabatic excited state molecular dynamics simulations uncovers a critical role played by the different side groups in the two molecules in governing the intramolecular redistribution of excited state wavefunction, leading, in turn, to different time-scales.This is achieved via selective participation of specific atomic groups and complex global migration of the wavefunction from the outer to inner ring, which may have important implications for biological light-harvesting function.

View Article: PubMed Central - PubMed

Affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University, Saint Louis, Missouri 63130, USA.

ABSTRACT
Nonradiative relaxation of high-energy excited states to the lowest excited state in chlorophylls marks the first step in the process of photosynthesis. We perform ultrafast transient absorption spectroscopy measurements, that reveal this internal conversion dynamics to be slightly slower in chlorophyll B than in chlorophyll A. Modeling this process with non-adiabatic excited state molecular dynamics simulations uncovers a critical role played by the different side groups in the two molecules in governing the intramolecular redistribution of excited state wavefunction, leading, in turn, to different time-scales. Even given smaller electron-vibrational couplings compared to common organic conjugated chromophores, these molecules are able to efficiently dissipate about 1 eV of electronic energy into heat on the timescale of around 200 fs. This is achieved via selective participation of specific atomic groups and complex global migration of the wavefunction from the outer to inner ring, which may have important implications for biological light-harvesting function.

No MeSH data available.


Related in: MedlinePlus