Energy Transfer and Connectivity in Chloroplasts:  Competition between Trapping and Annihilation in Pulsed Fluorescence Induction Experiments

Valkūnas, Leonas; Cervinskas, V.; Mourik, Frank van

doi:10.1021/jp970641p

Cited by 10 publications

(5 citation statements)

References 27 publications

(99 reference statements)

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“…Calculations using the equations derived above show that the mixing of the ground state and the excited state with the higher ͑nonresonant͒ excited states does not have much influence on the ground state one-photon absorption for the homodimer. 22,23 This result is in line with the results obtained for molecular aggregates by taking into account the mixing with the two-exciton states. 30 The effect for the homodimer is presented in Fig.…”

Section: Demonstration Of the Excited State Mixingsupporting

confidence: 90%

“…Such kind of interactions could appear for the coupled monomers containing more than two energy levels. The difference spectra of the homodimer built-up by Bchl molecules 22,23 and the circular dichroism ͑CD͒ spectrum of the homodimer 24 were already discussed. The general theory of the nonlinear optical response of aggregates is already developed.…”

Section: Introductionmentioning

confidence: 99%

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Effects of excited state mixing on transient absorption spectra in dimers: Application to photosynthetic light-harvesting complex II

Valkūnas

Cervinskas

Trinkunas

et al. 1999

The Journal of Chemical Physics

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The excited state mixing effect is taken into account considering the difference spectra of dimers. Both the degenerate ͑homo͒ dimer as well as the nondegenerate ͑hetero͒ dimer are considered. Due to the higher excited state mixing with the two-exciton states in the homodimer, the excited state absorption ͑or the difference spectrum͒ can be strongly affected in comparison with the results obtained in the Heitler-London approximation. The difference spectrum of the heterodimer is influenced by two resonance effects ͑i͒ mixing of the ground state optical transitions of both monomers in the dimer and ͑ii͒ mixing of the excited state absorption of the excited monomer with the ground state optical transition in the nonexcited monomer. These effects have been tested by simulating the difference absorption spectra of the light-harvesting complex of photosystem II ͑LHC II͒ experimentally obtained with the 60 fs excitation pulses at zero delay times and various excitation wavelengths. The pairs of coupled chlorophylls a and b for simulations have been taken from the best LHC II assignment model obtained by simulating the steady-state spectra and the transient absorption at various excitation wavelengths. Qualitatively the spectral peculiarities of the difference spectra are explained by means of the resonance interpigment interactions, which are responsible for the excited state mixing.

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Section: Demonstration Of the Excited State Mixingsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Effects of excited state mixing on transient absorption spectra in dimers: Application to photosynthetic light-harvesting complex II

Valkūnas

Cervinskas

Trinkunas

et al. 1999

The Journal of Chemical Physics

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“…As a result, the whole aggregate can be viewed as a single supermolecule which is fully characterized by a manifold of various accessible energy levels reflecting single and multiple excitations. 26,27,48,49 The resulting stochastic model describing possible transitions between these energy levels has been successfully used to describe non-linear S-S annihilation in LHCII trimers. 32,33 At a high repetition rate of the excitation laser, the formation of triplet states should also be considered, which requires the extension of the stochastic model of an LHCII supermolecule.…”

Section: Resultsmentioning

confidence: 99%

Singlet–triplet annihilation in single LHCII complexes

Gruber

Chmeliov

Krüger

et al. 2015

Phys. Chem. Chem. Phys.

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In light harvesting complex II (LHCII) of higher plants and green algae, carotenoids (Cars) have an important function to quench chlorophyll (Chl) triplet states and therefore avoid the production of harmful singlet oxygen. The resulting Car triplet states lead to a non-linear self-quenching mechanism called singlet-triplet (S-T) annihilation that strongly depends on the excitation density. In this work we investigated the fluorescence decay kinetics of single immobilized LHCIIs at room temperature and found a two-exponential decay with a slow (3.5 ns) and a fast (35 ps) component. The relative amplitude fraction of the fast component increases with increasing excitation intensity, and the resulting decrease in the fluorescence quantum yield suggests annihilation effects. Modulation of the excitation pattern by means of an acousto-optic modulator (AOM) furthermore allowed us to resolve the time-dependent accumulation and decay rate (∼7 μs) of the quenching species. Inspired by singlet-singlet (S-S) annihilation studies, we developed a stochastic model and then successfully applied it to describe and explain all the experimentally observed steady-state and time-dependent kinetics. That allowed us to distinctively identify the quenching mechanism as S-T annihilation. Quantitative fitting resulted in a conclusive set of parameters validating our interpretation of the experimental results. The obtained stochastic model can be generalized to describe S-T annihilation in small molecular aggregates where the equilibration time of excitations is much faster than the annihilation-free singlet excited state lifetime.

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“…While this agrees with the findings of Hemelrijk and van Gorkom (1992) as well as of Lavergne and Rappaport (1998), it calls for a reevaluation of the data of France et al (1992) and their interpretation. Actually, based on model calculations Valkunas et al (1997) already concluded more than 25 years ago that singlet-triplet annihilation is "a more natural explanation for the observations of France et al (1992) than the two-hit model of Valkunas et al (1991)". This explanation is in line with our findings on the lowering of fluorescence yield by HIQ (see preceding section).…”

Section: Saturation Of St-induced Variable Fluorescence Yieldmentioning

confidence: 99%

Flash-kinetics as a complementary analytical tool in PAM fluorimetry

Klughammer,

Schlosser,

Schreiber

2024

Photosynth Res

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A new measuring system based on the already existing Multi-Color-PAM Fluorimeter (Schreiber et al. in Photosynth Res 113:127–144, 2012) was developed that in addition to standard PAM measurements enables pump-and-probe flash measurements and allows simultaneous measurements of the changes in chlorophyll fluorescence yield (F) during application of saturating flashes (ST). A high-power Chip-on-Board LED array provides ST flashes with close to rectangular profiles at wide ranges of widths (0.5 µs to 5 ms), intensities (1.3 mmol to 1.3 mol 440 nm quanta m−2 s−1) and highly flexible repetition times. Using a dedicated rising-edge profile correction, sub-µs time resolution is obtained for assessment of initial fluorescence and rise kinetics. At maximal to moderate flash intensities the flash-kinetics (changes of F during course of ST, STK) are strongly affected by ‘High Intensity Quenching’ (HIQ), consisting of Car-triplet quenching, TQ, and donor-side-dependent quenching, DQ. The contribution of TQ is estimated by application of a second ST after 20 µs dark-time. Upon application of flash trains (ST sequences with defined repetition times) typical period-4 oscillations in dark fluorescence yield (F0) and ST-induced fluorescence yield, FmST, are obtained which can be measured in vivo both with suspensions and from the surface of leaves. Examples of application with dilute suspensions of Chlorella and an intact dandelion leaf are presented. It is shown that weak far-red light (730–740 nm) advances the S-state distribution of the water-splitting system by one step, resulting in substantial lowering of FmST and also of the I1-level in the polyphasic rise of fluorescence yield induced by a multiple-turnover flash (MT). Based on comparative measurements of STK and the polyphasic rise kinetics with the same Chlorella sample, it is concluded that the generally observed lower values of maximal fluorescence yields using ST-protocols compared to MT-protocols are due to a higher extent of HIQ (mainly DQ) and the contribution of variable PSI fluorescence to FmST.

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Energy Transfer and Connectivity in Chloroplasts: Competition between Trapping and Annihilation in Pulsed Fluorescence Induction Experiments

Cited by 10 publications

References 27 publications

Effects of excited state mixing on transient absorption spectra in dimers: Application to photosynthetic light-harvesting complex II

Effects of excited state mixing on transient absorption spectra in dimers: Application to photosynthetic light-harvesting complex II

Singlet–triplet annihilation in single LHCII complexes

Flash-kinetics as a complementary analytical tool in PAM fluorimetry

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