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Solvent-Dependent Characterization of Fucoxanthin through 2D Electronic Spectroscopy Reveals New Details on the Intramolecular Charge-Transfer State Dynamics.

ABSTRACT: The electronic state manifolds of carotenoids and their relaxation dynamics are the object of intense investigation because most of the subtle details regulating their photophysics are still unknown. In order to contribute to this quest, here, we present a solvent-dependent 2D Electronic Spectroscopy (2DES) characterization of fucoxanthin, a carbonyl carotenoid involved in the light-harvesting process of brown algae. The 2DES technique allows probing its ultrafast relaxation dynamics in the first 1000 fs after photoexcitation with a 10 fs time resolution. The obtained results help shed light on the dynamics of the first electronic state manifold and, in particular, on an intramolecular charge-transfer state (ICT), whose photophysical properties are particularly elusive given its (almost) dark nature.

SUBMITTER: Marcolin G

PROVIDER: S-EPMC8279730 | biostudies-literature | 2021 May

REPOSITORIES: biostudies-literature

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Solvent-Dependent Characterization of Fucoxanthin through 2D Electronic Spectroscopy Reveals New Details on the Intramolecular Charge-Transfer State Dynamics.

Marcolin Giampaolo G Collini Elisabetta E

The journal of physical chemistry letters 20210517 20

The electronic state manifolds of carotenoids and their relaxation dynamics are the object of intense investigation because most of the subtle details regulating their photophysics are still unknown. In order to contribute to this quest, here, we present a solvent-dependent 2D Electronic Spectroscopy (2DES) characterization of fucoxanthin, a carbonyl carotenoid involved in the light-harvesting process of brown algae. The 2DES technique allows probing its ultrafast relaxation dynamics in the firs ...[more]

PMID: 33999637

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Project description:Fucoxanthin chlorophyll-a/c 2 protein (FCP), the membrane-intrinsic light harvesting complex from the diatom Cyclotella meneghiniana, is characterized by Stark spectroscopy to obtain a quantitative measure of the excited-state dipolar properties of the constituent pigments. The electro-optical properties of the carotenoid fucoxanthin (Fx), the primary light harvester in FCP, were determined from the Stark spectrum measured in a MeTHF glass (77 K) and compared to the results from electronic-structure calculations. On photon absorption by Fx, a 17 D change in the static dipole moment (|Delta mu|exp), and a somewhat larger |Delta mu|exp at the red edge, are measured for the S 0 --> S 2 (1 (1)A g (-)-like -->1 (1)B u *+-like) transition. The large change in dipole moment indicates that Fx undergoes photoinduced charge transfer (CT), and underscores the influence of the S 2 state on the polarity-dependent excited-state dynamics of Fx that has so far been attributed to, and discussed in terms of, the S 0 and the S 1/ICT states. MNDO-PSDCI and SACCI-CISD calculations indicate that the 1 (1)B u (*+)-like state intrinsically possesses a dipole moment much smaller than the 2 (1)A g (*-)-like state, suggesting that solvent fields promote the mixing of these two states and could account for the large dipole moments measured here for the S 0 --> S 2 transition. These CT properties of the 1 (1)B u (*+)-like state of Fx are further enhanced in the protein and underpin its photosynthetic capabilities for light harvesting and energy transfer (ET). In FCP, the CT properties of the Fx's vary according to the energetic position: between 450 and 500 nm there appear to be two sets of Fx's that exhibit |Delta mu| exp values on the order of 5 and 15 D, whereas the red-most Fx's, that are very efficient in ET to chlorophyll-a (Chl-a), exhibit strikingly large |Delta mu| exp values on the order of 40 D. Such magnitudes of |Delta mu| exp suggest a mechanism that enhances Coulombic coupling to promote ET from the S 2 state of Fx to Chl-a. These three sets of Fx's, including a fourth red Fx, are identified by fitting the Stark spectrum of FCP with the Stark spectrum of Fx in MeTHF. In contrast to the Fx's in the protein, the electrostatic properties of the Chl's in FCP are comparatively much smaller. Notably, for the Q y band of Chl-a, a |Delta mu| exp of 0.92 D and a change in polarizability ( Delta alpha exp) of 20 A (3), indicate that the Chl-a's are monomeric in nature and decoupled from each other.

Dataset Information

Solvent-Dependent Characterization of Fucoxanthin through 2D Electronic Spectroscopy Reveals New Details on the Intramolecular Charge-Transfer State Dynamics.

Publications

Solvent-Dependent Characterization of Fucoxanthin through 2D Electronic Spectroscopy Reveals New Details on the Intramolecular Charge-Transfer State Dynamics.

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