1
|
Ishizaki A, Fleming GR. Insights into Photosynthetic Energy Transfer Gained from Free-Energy Structure: Coherent Transport, Incoherent Hopping, and Vibrational Assistance Revisited. J Phys Chem B 2021; 125:3286-3295. [PMID: 33724833 DOI: 10.1021/acs.jpcb.0c09847] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Giant strides in ultrashort laser pulse technology have enabled real-time observation of dynamical processes in complex molecular systems. Specifically, the discovery of oscillatory transients in the two-dimensional electronic spectra of photosynthetic systems stimulated a number of theoretical investigations exploring the possible physical mechanisms of the remarkable quantum efficiency of light harvesting processes. In this work, we revisit the elementary aspects of environment-induced fluctuations in the involved electronic energies and present a simple way to understand energy flow with the intuitive picture of relaxation in a funnel-type free-energy landscape. The presented free-energy description of energy transfer reveals that typical photosynthetic systems operate in an almost barrierless regime. The approach also provides insights into the distinction between coherent and incoherent energy transfer and the criteria by which the necessity of the vibrational assistance is considered.
Collapse
Affiliation(s)
- Akihito Ishizaki
- Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki 444-8585, Japan.,School of Physical Sciences, Graduate University for Advanced Studies, Okazaki 444-8585, Japan
| | - Graham R Fleming
- Department of Chemistry, University of California, Berkeley, California 94720, United States.,Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.,Kavli Energy NanoSciences Institute at Berkeley, Berkeley, California 94720, United States
| |
Collapse
|
2
|
Maiuri M, Ostroumov EE, Saer RG, Blankenship RE, Scholes GD. Coherent wavepackets in the Fenna-Matthews-Olson complex are robust to excitonic-structure perturbations caused by mutagenesis. Nat Chem 2018; 10:177-183. [PMID: 29359758 DOI: 10.1038/nchem.2910] [Citation(s) in RCA: 81] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Accepted: 11/15/2017] [Indexed: 01/24/2023]
Abstract
Femtosecond pulsed excitation of light-harvesting complexes creates oscillatory features in their response. This phenomenon has inspired a large body of work aimed at uncovering the origin of the coherent beatings and possible implications for function. Here we exploit site-directed mutagenesis to change the excitonic level structure in Fenna-Matthews-Olson (FMO) complexes and compare the coherences using broadband pump-probe spectroscopy. Our experiments detect two oscillation frequencies with dephasing on a picosecond timescale-both at 77 K and at room temperature. By studying these coherences with selective excitation pump-probe experiments, where pump excitation is in resonance only with the lowest excitonic state, we show that the key contributions to these oscillations stem from ground-state vibrational wavepackets. These experiments explicitly show that the coherences-although in the ground electronic state-can be probed at the absorption resonances of other bacteriochlorophyll molecules because of delocalization of the electronic excitation over several chromophores.
Collapse
Affiliation(s)
- Margherita Maiuri
- Department of Chemistry, Princeton University, Washington Road, Princeton, New Jersey 08544, USA
| | - Evgeny E Ostroumov
- Department of Chemistry, Princeton University, Washington Road, Princeton, New Jersey 08544, USA
| | - Rafael G Saer
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri 63130, USA.,Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, Missouri 63130, USA
| | - Robert E Blankenship
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri 63130, USA.,Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, Missouri 63130, USA.,Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri 63130, USA
| | - Gregory D Scholes
- Department of Chemistry, Princeton University, Washington Road, Princeton, New Jersey 08544, USA
| |
Collapse
|
3
|
Fujihashi Y, Ishizaki A. Fluctuations in Electronic Energy Affecting Singlet Fission Dynamics and Mixing with Charge-Transfer State: Quantum Dynamics Study. J Phys Chem Lett 2016; 7:363-369. [PMID: 26732701 DOI: 10.1021/acs.jpclett.5b02678] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Singlet fission is a spin-allowed process by which a singlet excited state is converted to two triplet states. To understand mechanisms of the ultrafast fission via a charge transfer (CT) state, one has investigated the dynamics through quantum-dynamical calculations with the uncorrelated fluctuation model; however, the electronic states are expected to experience the same fluctuations induced by the surrounding molecules because the electronic structure of the triplet pair state is similar to that of the singlet state except for the spin configuration. Therefore, the fluctuations in the electronic energies could be correlated, and the 1D reaction coordinate model may adequately describe the fission dynamics. In this work we develop a model for describing the fission dynamics to explain the experimentally observed behaviors. We also explore impacts of fluctuations in the energy of the CT state on the fission dynamics and the mixing with the CT state. The overall behavior of the dynamics is insensitive to values of the reorganization energy associated with the transition from the singlet state to the CT state, although the coherent oscillation is affected by the fluctuations. This result indicates that the mixing with the CT state is rather robust under the fluctuations in the energy of the CT state as well as the high-lying CT state.
Collapse
Affiliation(s)
- Yuta Fujihashi
- Institute for Molecular Science, National Institutes of Natural Sciences , Okazaki 444-8585, Japan
| | - Akihito Ishizaki
- Institute for Molecular Science, National Institutes of Natural Sciences , Okazaki 444-8585, Japan
| |
Collapse
|