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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

Molecular structure of chlorophylls a and b.Carbon atoms are labeled according to the IUPAC convention for porphyrins, with the standard x- and y- axes of Gouterman’s four-orbital theory shown. Constituent groups at the R3 and R7 positions are shown in the lower right corner of the diagram. Chlorophyll phytyl tails (R) are not shown.
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f1: Molecular structure of chlorophylls a and b.Carbon atoms are labeled according to the IUPAC convention for porphyrins, with the standard x- and y- axes of Gouterman’s four-orbital theory shown. Constituent groups at the R3 and R7 positions are shown in the lower right corner of the diagram. Chlorophyll phytyl tails (R) are not shown.

Mentions: In this work, we focus on studying theoretically and experimentally, the intramolecular relaxation of photoexcited states of two important chlorophyll molecules - ChlA and chlorophyll b (ChlB), shown in Fig. 1. ChlA is the most abundant natural photosynthetic pigment that is found in every green plant, followed in abundance by ChlB1. Structurally, these two chlorophyll pigments differ only by an extra carbonyl oxygen at the R7 position (ChlB), yet are known to exhibit marked differences in their absorption spectra. We have systematically investigated the B to Q-band internal conversion processes in these two molecules by employing Non-Adiabatic Excited State Molecular Dynamics (NA-ESMD) simulations. This methodology has been successfully used to simulate the ultrafast intramolecular redistribution and relaxation of the excess of electronic energy after photoexcitation in many large organic conjugated chromophores363738. The role played by relatively minor structural differences between these molecules in the dynamics of relaxation of high-energy excited states has been revealed via analysis based on evolution of transition density localization.


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)

Molecular structure of chlorophylls a and b.Carbon atoms are labeled according to the IUPAC convention for porphyrins, with the standard x- and y- axes of Gouterman’s four-orbital theory shown. Constituent groups at the R3 and R7 positions are shown in the lower right corner of the diagram. Chlorophyll phytyl tails (R) are not shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Molecular structure of chlorophylls a and b.Carbon atoms are labeled according to the IUPAC convention for porphyrins, with the standard x- and y- axes of Gouterman’s four-orbital theory shown. Constituent groups at the R3 and R7 positions are shown in the lower right corner of the diagram. Chlorophyll phytyl tails (R) are not shown.
Mentions: In this work, we focus on studying theoretically and experimentally, the intramolecular relaxation of photoexcited states of two important chlorophyll molecules - ChlA and chlorophyll b (ChlB), shown in Fig. 1. ChlA is the most abundant natural photosynthetic pigment that is found in every green plant, followed in abundance by ChlB1. Structurally, these two chlorophyll pigments differ only by an extra carbonyl oxygen at the R7 position (ChlB), yet are known to exhibit marked differences in their absorption spectra. We have systematically investigated the B to Q-band internal conversion processes in these two molecules by employing Non-Adiabatic Excited State Molecular Dynamics (NA-ESMD) simulations. This methodology has been successfully used to simulate the ultrafast intramolecular redistribution and relaxation of the excess of electronic energy after photoexcitation in many large organic conjugated chromophores363738. The role played by relatively minor structural differences between these molecules in the dynamics of relaxation of high-energy excited states has been revealed via analysis based on evolution of transition density localization.

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