On the origin of oscillations in two-dimensional spectra of excitonically-coupled molecular systems

Duan, Hong-Guang; Nalbach, P.; Prokhorenko, Valentyn I.; Mukamel, Shaul; Thorwart, Michael

doi:10.1088/1367-2630/17/7/072002

Cited by 40 publications

(81 citation statements)

References 48 publications

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“…In conclusion, we have shown that, under ambient physical conditions, it is irrelevant for the life- Even under (unrealistically) weak electronic dephasing, the electronic coherence lifetime is not enhanced by the vibronic components. The same conclusion has been drawn from the study of indocarbocyanine dye molecules 33 . In addition, we find that a strong mixing of electronic and anticorrelated vibrational components of the wavefunction due to strong vibronic coupling does not enhance the vibrational amplitude at long times under ambient conditions.…”

Section: Discussionsupporting

confidence: 76%

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Does electronic coherence enhance anticorrelated pigment vibrations under realistic conditions?

Duan

Thorwart

Miller

2019

The Journal of Chemical Physics

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The light-harvesting efficiency of a photoactive molecular complex is largely determined by the properties of its electronic quantum states. Those, in turn, are influenced by molecular vibrational states of the nuclear degrees of freedom. Here, we reexamine two recently formulated concepts that a coherent vibronic coupling between molecular states would either extend the electronic coherence lifetime or enhance the amplitude of the anticorrelated vibrational mode at longer times. For this, we study a vibronically coupled dimer and calculate the nonlinear two-dimensional (2D) electronic spectra which directly reveal electronic coherence. The timescale of electronic coherence is initially extracted by measuring the antidiagonal bandwidth of the central peak in the 2D spectrum at zero waiting time. Based on 1 the residual analysis, we identify small-amplitude long-lived oscillations in the cross-peaks, which, however, are solely due to groundstate vibrational coherence, regardless of having resonant or off-resonant conditions. Our studies neither show an enhancement of the electronic quantum coherence nor an enhancement of the anticorrelated vibrational mode by the vibronic coupling under ambient conditions.In the initial steps of photosynthesis, photoactive molecular complexes capture the sunlight energy and transfer it to the reaction center on an ultrafast time scale and with unity quantum efficiency 1 . The performance is determined by the molecular electronic properties, in concert with the molecular vibrations and coupling to the environment given by a solvent and the surrounding pigments and proteins. To investigate the energy transfer, ultrafast 2D electronic spectroscopy 2-4 is able to resolve fs time scales. It is able to reveal the interactions between the energetically closeby lying molecular electronic states, for which the linear spectra are commonly highly congested and broadened by the strong static disorder 5 . Recent experimental studies of the Fenna-Matthews-Olson (FMO) complex reported long-lived oscillations of the cross-peaks both at low 6 and at room temperature 7 which have been assigned to enhanced electronic coherence. This has generated tremendous interest in this new field of quantum biology 8 , aiming to reveal a functional connection between photosynthetic energy transfer and long-lived quantum coherence. Moreover, also in photoactive marine cryptophyte algae 9 , the light-harvesting complex LHCII 10 and in the Photosystem II reaction center 11, 12 , long-lived oscillations have been experimentally reported at low and room temperature.

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Section: Discussionsupporting

confidence: 76%

“…In addition to the electronic coherence, signatures of the vibrational coherence of the pigmentprotein host can also be accessed on the same spectroscopic footing [26][27][28][29] . Yet, electronic coherence can be distinguished from vibrational coherence 30,33,34 . Long-lived pure electronic coherence is unexpected to exist in most light harvesting complexes.…”

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confidence: 99%

Does electronic coherence enhance anticorrelated pigment vibrations under realistic conditions?

Duan

Thorwart

Miller

2019

The Journal of Chemical Physics

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“…An additional strong coupling of the excitonic to the nuclear degrees of freedom was also considered (31-39) as a possible driving source of coherence. Such a mechanism can yield longer-lived oscillations of the cross-peak amplitude (40,41), yet, a strong vibronic coupling is required, and the oscillation amplitudes typically remain small. Moreover, in general, electronic coherence could only be enhanced by vibrational coherence if it lives at least as long It is used as a consistence check for the electronic dephasing time.…”

Section: Significancementioning

confidence: 99%

Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer

Duan

Prokhorenko

Cogdell

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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286

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During the first steps of photosynthesis, the energy of impinging solar photons is transformed into electronic excitation energy of the light-harvesting biomolecular complexes. The subsequent energy transfer to the reaction center is commonly rationalized in terms of excitons moving on a grid of biomolecular chromophores on typical timescales <100 fs. Today's understanding of the energy transfer includes the fact that the excitons are delocalized over a few neighboring sites, but the role of quantum coherence is considered as irrelevant for the transfer dynamics because it typically decays within a few tens of femtoseconds. This orthodox picture of incoherent energy transfer between clusters of a few pigments sharing delocalized excitons has been challenged by ultrafast optical spectroscopy experiments with the FennaMatthews-Olson protein, in which interference oscillatory signals up to 1.5 ps were reported and interpreted as direct evidence of exceptionally long-lived electronic quantum coherence. Here, we show that the optical 2D photon echo spectra of this complex at ambient temperature in aqueous solution do not provide evidence of any long-lived electronic quantum coherence, but confirm the orthodox view of rapidly decaying electronic quantum coherence on a timescale of 60 fs. Our results can be considered as generic and give no hint that electronic quantum coherence plays any biofunctional role in real photoactive biomolecular complexes. Because in this structurally well-defined protein the distances between bacteriochlorophylls are comparable to those of other light-harvesting complexes, we anticipate that this finding is general and directly applies to even larger photoactive biomolecular complexes.T he principle laws of physics undoubtedly also govern the principle mechanisms of biology. The animate world consists of macroscopic and dynamically slow structures with a huge number of degrees of freedom, such that the laws of statistical mechanics apply. Conversely, the fundamental theory of the microscopic building blocks is quantum mechanics. The physics and chemistry of large molecular complexes may be considered as a bridge between the molecular world and the formation of living matter. A fascinating question since the early days of quantum theory is on the borderline between the atomistic quantum world and the classical world of biology. Clearly, the conditions under which matter displays quantum features or biological functionality are contrarious. Quantum coherent features only become apparent when systems with a few degrees of freedom with a preserved quantum mechanical phase relation of a wave function are well shielded from environmental fluctuations that otherwise lead to rapid dephasing. This dephasing mechanism is very efficient at ambient temperatures, at which biological systems operate. Also, the function of biological macromolecular systems relies on their embedding in a "wet" and highly polar solvent environment, which is again hostile to any quantum coherence. Therefore, the common view ...

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“…A long-standing problem in molecular spectroscopy is to understand the roles of nuclear vibrations in the electronic structure of interacting molecules (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Since the early work of Förster, Kasha, Fulton and Gouterman (2,(14)(15)(16), it has been recognized that the absorption spectra of interacting molecules can appear strikingly different than that of the constituent monomers, particularly when the monomer spectrum exhibits a pronounced vibronic progression, which is due to the coupling between electronic and vibrational motion (17)(18)(19).…”

Section: Introductionmentioning

confidence: 99%

Temperature-dependent conformations of exciton-coupled Cy3 dimers in double-stranded DNA

Kringle

Sawaya

Widom

et al. 2018

The Journal of Chemical Physics

133

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Understanding the properties of electronically interacting molecular chromophores, which involve internally coupled electronic-vibrational motions, is important to the spectroscopy of many biologically relevant systems. Here we apply linear absorption, circular dichroism, and two-dimensional fluorescence spectroscopy to study the polarized collective excitations of excitonically coupled cyanine dimers (Cy3) that are rigidly positioned within the opposing sugar-phosphate backbones of the double-stranded region of a double-stranded (ds)-single-stranded (ss) DNA fork construct. We show that the exciton-coupling strength of the (Cy3)-DNA construct can be systematically varied with temperature below the ds-ss DNA denaturation transition. We interpret spectroscopic measurements in terms of the Holstein vibronic dimer model, from which we obtain information about the local conformation of the (Cy3) dimer, as well as the degree of static disorder experienced by the Cy3 monomer and the (Cy3) dimer probe locally within their respective DNA duplex environments. The properties of the (Cy3)-DNA construct we determine suggest that it may be employed as a useful model system to test fundamental concepts of protein-DNA interactions and the role of electronic-vibrational coherence in electronic energy migration within exciton-coupled bio-molecular arrays.

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On the origin of oscillations in two-dimensional spectra of excitonically-coupled molecular systems

Cited by 40 publications

References 48 publications

Does electronic coherence enhance anticorrelated pigment vibrations under realistic conditions?

Does electronic coherence enhance anticorrelated pigment vibrations under realistic conditions?

Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer

Temperature-dependent conformations of exciton-coupled Cy3 dimers in double-stranded DNA

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