Site-selection optical spectra of bacteriochlorophyll and bacteriopheophytin in frozen solutions

Renge, Indrek; Mauring, Koit; Avarmaa, R.

doi:10.1016/0022-2313(87)90161-x

Cited by 51 publications

(68 citation statements)

References 22 publications

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“…A 367 cm -1 mode is found in the frequency-integrated data while a 394 cm -1 mode is seen in the signal detected at 12050 cm -1 . These two frequencies are probably due to vibrational modes and not to exciton splittings, as resonance Raman 66 and lowtemperature fluorescence excitation spectra 78 of monomeric BChl a show several peaks in this frequency range. In the 12050 cm -1 PPA signal a 241 cm -1 frequency is also observed.…”

Section: Discussionmentioning

confidence: 99%

Exciton Delocalization and Initial Dephasing Dynamics of Purple Bacterial LH2

et al. 2000

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Ultrafast four-wave mixing spectroscopies are employed to study exciton dynamics associated with the B800 and B850 transitions of LH2 from Rhodobacter sphaeroides. Bacteriochlorophyll a , the constituent chromophore of the B800 and B850 aggregates, is studied as a monomer in solution for comparison. Frequency-resolved pump-probe spectra measured across the B800 and B850 bands establish that at zero delay the transition dipole moment of B850 is substantially larger than that of B800, indicating an initial coherence size of ∼13 chromophores in the (18-member) B850 aggregate. Novel frequency-resolved stimulated photon echo measurements show that intermolecular interactions in the B850 ring reduce the coupling of this band's electronic transition to nuclear motion. In contrast, linear electron-nuclear coupling is comparable in the bacteriochlorophyll a monomer and B800, where exciton coupling is weak. Photon echo peak shift data are consistent with these observations. The initial localization dynamics of the B850 exciton are resolved with transient grating and pump-probe magic angle measurements. These data show that the enhanced transition dipole moment of B850 at the moment of excitation contracts significantly with a time constant of ∼50 fs (for transient grating) due to exciton dephasing resulting in localization. Pump-probe anisotropy measurements reveal substantial transition dipole moment orientational relaxation with nearly the same time constant. These experimental data will be useful for the development of a rigorous theoretical picture of ultrafast exciton dynamics in LH2. B850's large transition dipole moment for absorption may play an important role in the biological function of LH2, as it would enhance the energy transfer rate between B800 and B850.

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Section: Discussionmentioning

confidence: 99%

Exciton Delocalization and Initial Dephasing Dynamics of Purple Bacterial LH2

et al. 2000

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“…Although the calculation is approximate, it serves to illustrate that the picosecond transfer time can be achieved with an intramolecular mode whose FC factor is only 0.05. (A value of 0.05 is, however, a maximum for the FranckCondon active modes of BChl a (Renge et al 1987;Gillie et al 1989). ) In Equation (1) there are six variables that can, in principle, carry a pressure dependence: V, S, win, F, Y. and f~o-Our hole spectra indicate that, at the pressures used, S and wm are essentially pressure independent.…”

Section: Pressure Independence Of the B800--~ B850 Energy Transfer Ratementioning

confidence: 99%

“…If there were no Franck--Condon activity near 900 cm -1, then from Equation (1) it follows that there should be a reduction in the rate by at least a factor of 2. However, there are three closely spaced modes near 920 cm -1 whose combined Franck-Condon factor equals that of the 750 cm-1 mode (0.05) (Renge et al 1987;Reddy et al 1991). Thus, what we appear to have accomplished with pressure is mode-switching in FOrster transfer whereby the 750 cm -1 mode is supplanted by the 920 cm -1 modes.…”

mentioning

confidence: 99%

High pressure studies of energy transfer and strongly coupled bacteriochlorophyll dimers in photosynthetic protein complexes

Reddy

Jankowiak

et al. 1996

Photosynth Res

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High pressure is used with hole burning and absorption spectroscopies at low temperatures to study the pressure dependence of the B800--+B850 energy transfer rate in the LH2 complex of Rhodobacter sphaeroides and to assess the extent to which pressure can be used to identify and characterize states associated with strongly coupled chlorophyll molecules. Pressure tuning of the B800-B850 gap from ,-~ 750 cm-1 at 0.1 MPa to ,,~ 900 cm-1 at 680 MPa has no measurable effect on the 2 ps energy transfer rate of the B800-B850 complex at 4.2 K. An explanation for this resilience against pressure, which is supported by earlier hole burning studies, is provided. It is based on weak coupling nonadiabatic transfer theory and takes into account the inhomogeneous width of the B800-B850 energy gap, the large homogeneous width of the B850 band from exciton level structure and the Franck-Condon factors of acceptor protein phonons and intramolecular BChl a modes. The model yields reasonable agreement with the 4.2 K energy transfer rate and is consistent with its weak temperature dependence. It is assumed that it is the C9-ring exciton levels which lie within the B850 band that are the key acceptor levels, meaning that BChl a modes are essential to the energy transfer process. These ring exciton levels derive from the strongly allowed lowest energy component of the basic B850 dimer. However, the analysis of B850s linear pressure shift suggests that another F6rster pathway may also be important. It is one that involves the ring exciton levels derived from the weakly allowed upper component of the B850 dimer which we estimate to be quasi-degenerate with B800. In the second part of the paper, which is concerned with strong BChl monomer-monomer interactions of dimers, we report that the pressure shifts of B875 (LH2), the primary donor absorption bands of bacterial RC (P870 of Rb. sphaeroides and P960 of Rhodopseudomonas viridis) and B 1015 (LH complex of Rps. viridis) are equal and large in value (,,~ -0.4 cm°l/MPa at 4.2 K) relative to those of isolated monomers in polymers and proteins (< -0.1 cm°l/MPa). The shift rate for B850 at 4.2 K is -0.28 cm-l/MPa. A model is presented which appears to be capable of providing a unified explanation for the pressure shifts.Abbreviations: B800-BChl antenna band absorbing (at room temperature) at 800 nm (B850, B875, B 1015 are defined similarly) CD -circular dichroism; FC factor-Franck-Condon factor; FMO complex-Fenna-MatthewsOlson complex; L-S theory-Laird-Skinner theory; LH 1 -core light-harvesting complex of the BChl antenna complexes; LH2-peripheral light-harvesting complex of the BChl antenna complexes; NPHB -non-photochemical hole burning; P960-absorption band of special pair of Rhodopseudomonas viridis absorbing at 960 nm (room temperature). P870 of Rhodobacter sphaeroides is defined similarly; QM/MM results -quantum mechanical/molecular mechanical results; RC-reaction center; ZPH-zero phonon hole 278

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“…43,44 As a result, electronic excitation causes small changes in the equilibrium vibrational coordinates (less than the root mean square zero point motion) and the vibrational frequencies change only a few percent upon electronic excitation. 45,46 Accordingly, the vibrational motion in an isolated pigment is of small amplitude and, for short times, can be approximated as harmonic, with the same frequency ω i on all electronic states. Similar circumstances apply to chromophores in quantum confined systems such as semiconductor nanocrystals 47 and carbon nanotubes 48 but not to many organic polymers.…”

Section: A Dimer With Intramolecular Environmental and Mixed Vibramentioning

confidence: 99%

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. I. Theory for a dimer

Tiwari

Jonas

2017

The Journal of Chemical Physics

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Non-adiabatic vibrational-electronic resonance in the excited electronic states of natural photosynthetic antennas drastically alters the adiabatic framework, in which electronic energy transfer has been conventionally studied, and suggests the possibility of exploiting non-adiabatic dynamics for directed energy transfer. Here, a generalized dimer model incorporates asymmetries between pigments, coupling to the environment, and the doubly excited state relevant for nonlinear spectroscopy. For this generalized dimer model, the vibrational tuning vector that drives energy transfer is derived and connected to decoherence between singly excited states. A correlation vector is connected to decoherence between the ground state and the doubly excited state. Optical decoherence between the ground and singly excited states involves linear combinations of the correlation and tuning vectors. Excitonic coupling modifies the tuning vector. The correlation and tuning vectors are not always orthogonal, and both can be asymmetric under pigment exchange, which affects energy transfer. For equal pigment vibrational frequencies, the nonadiabatic tuning vector becomes an anti-correlated delocalized linear combination of intramolecular vibrations of the two pigments, and the nonadiabatic energy transfer dynamics become separable. With exchange symmetry, the correlation and tuning vectors become delocalized intramolecular vibrations that are symmetric and antisymmetric under pigment exchange. Diabatic criteria for vibrational-excitonic resonance demonstrate that anti-correlated vibrations increase the range and speed of vibronically resonant energy transfer (the Golden Rule rate is a factor of 2 faster). A partial trace analysis shows that vibronic decoherence for a vibrational-excitonic resonance between two excitons is slower than their purely excitonic decoherence.

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Site-selection optical spectra of bacteriochlorophyll and bacteriopheophytin in frozen solutions

Cited by 51 publications

References 22 publications

Exciton Delocalization and Initial Dephasing Dynamics of Purple Bacterial LH2

Exciton Delocalization and Initial Dephasing Dynamics of Purple Bacterial LH2

High pressure studies of energy transfer and strongly coupled bacteriochlorophyll dimers in photosynthetic protein complexes

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. I. Theory for a dimer

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