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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

Transient absorption of ChlA (solid black curve) and ChlB (dashed red curve) dissolved in ethanol, probed in the Qy region after excitation at 442 nm.(a) Typical transient absorption spectra recorded at delay time of 1 ps. (b) Typical transients recorded at 672 nm and 652 nm for ChlA and ChlB, respectively. The samples were diluted to OD ~ 0.8 at the pump wavelength. The signals corresponding to ChlB are multiplied by two.
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f2: Transient absorption of ChlA (solid black curve) and ChlB (dashed red curve) dissolved in ethanol, probed in the Qy region after excitation at 442 nm.(a) Typical transient absorption spectra recorded at delay time of 1 ps. (b) Typical transients recorded at 672 nm and 652 nm for ChlA and ChlB, respectively. The samples were diluted to OD ~ 0.8 at the pump wavelength. The signals corresponding to ChlB are multiplied by two.

Mentions: The dynamics of internal conversion in ChlA and ChlB solutions after excitation in the high energy B band was probed by femtosecond transient absorption (TA) spectroscopy (full details are given in Experimental). While both pigments are pumped at 442 nm, the probe wavelength are set to the respective Qy region. The TA spectra in Fig. 2(a) are characterized by a negative band with a maximum at 670 nm for ChlA and 650 nm for ChlB, due to ground-state bleaching and stimulated emission, and a positive signal below 650 nm due to excited-state absorption. From the kinetic traces of the negative TA in a 1 ps time window in Fig. 2(b), it is evident that the dynamics in both ChlA and ChlB is very similar. Both curves display an initial rapid increase of the signal followed by a second, slower phase. The initial rise depicts the appearance of ground-state bleaching following excitation in the B band by the 55 fs wide pump pulse. After the initial excitation, the slower rise is presumably due to stimulated emission appearing along with the population of the emitting lowest excited state (Qy). Thus, the slower rise of the TA signal reflects the dynamics of IC from the B band to Qy.


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)

Transient absorption of ChlA (solid black curve) and ChlB (dashed red curve) dissolved in ethanol, probed in the Qy region after excitation at 442 nm.(a) Typical transient absorption spectra recorded at delay time of 1 ps. (b) Typical transients recorded at 672 nm and 652 nm for ChlA and ChlB, respectively. The samples were diluted to OD ~ 0.8 at the pump wavelength. The signals corresponding to ChlB are multiplied by two.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Transient absorption of ChlA (solid black curve) and ChlB (dashed red curve) dissolved in ethanol, probed in the Qy region after excitation at 442 nm.(a) Typical transient absorption spectra recorded at delay time of 1 ps. (b) Typical transients recorded at 672 nm and 652 nm for ChlA and ChlB, respectively. The samples were diluted to OD ~ 0.8 at the pump wavelength. The signals corresponding to ChlB are multiplied by two.
Mentions: The dynamics of internal conversion in ChlA and ChlB solutions after excitation in the high energy B band was probed by femtosecond transient absorption (TA) spectroscopy (full details are given in Experimental). While both pigments are pumped at 442 nm, the probe wavelength are set to the respective Qy region. The TA spectra in Fig. 2(a) are characterized by a negative band with a maximum at 670 nm for ChlA and 650 nm for ChlB, due to ground-state bleaching and stimulated emission, and a positive signal below 650 nm due to excited-state absorption. From the kinetic traces of the negative TA in a 1 ps time window in Fig. 2(b), it is evident that the dynamics in both ChlA and ChlB is very similar. Both curves display an initial rapid increase of the signal followed by a second, slower phase. The initial rise depicts the appearance of ground-state bleaching following excitation in the B band by the 55 fs wide pump pulse. After the initial excitation, the slower rise is presumably due to stimulated emission appearing along with the population of the emitting lowest excited state (Qy). Thus, the slower rise of the TA signal reflects the dynamics of IC from the B band to Qy.

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