Mimicking Photosynthetic Electron and Energy Transfer

Gust, Devens; Moore, Thomas A.

doi:10.1002/9780470133460.ch1

Cited by 100 publications

(5 citation statements)

References 92 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Over the last three decades, many carotenotetrapyrrole synthetic dyads have been designed and synthesized in which the absorption of a photon is followed by the formation of the tetrapyrrole triplet species by intersystem crossing; subsequent T-TET from the tetrapyrrole to the carotenoid produces the carotenoid triplet species (9)(10)(11)(12). In these dyads, depending on their precise chemical properties and on the way the tetrapyrrole and the carotenoid molecules are linked, the T-TET kinetics ranges from tens of microseconds to the subnanosecond range.…”

Section: Significancementioning

confidence: 99%

Triplet–triplet energy transfer in artificial and natural photosynthetic antennas

Kish

Méndez-Hernández

et al. 2017

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

Self Cite

View full text Add to dashboard Cite

In photosynthetic organisms, protection against photooxidative stress due to singlet oxygen is provided by carotenoid molecules, which quench chlorophyll triplet species before they can sensitize singlet oxygen formation. In anoxygenic photosynthetic organisms, in which exposure to oxygen is low, chlorophyll-to-carotenoid triplet-triplet energy transfer (T-TET) is slow, in the tens of nanoseconds range, whereas it is ultrafast in the oxygen-rich chloroplasts of oxygen-evolving photosynthetic organisms. To better understand the structural features and resulting electronic coupling that leads to T-TET dynamics adapted to ambient oxygen activity, we have carried out experimental and theoretical studies of two isomeric carotenoporphyrin molecular dyads having different conformations and therefore different interchromophore electronic interactions. This pair of dyads reproduces the characteristics of fast and slow T-TET, including a resonance Raman-based spectroscopic marker of strong electronic coupling and fast T-TET that has been observed in photosynthesis. As identified by density functional theory (DFT) calculations, the spectroscopic marker associated with fast T-TET is due primarily to a geometrical perturbation of the carotenoid backbone in the triplet state induced by the interchromophore interaction. This is also the case for the natural systems, as demonstrated by the hybrid quantum mechanics/molecular mechanics (QM/MM) simulations of light-harvesting proteins from oxygenic (LHCII) and anoxygenic organisms (LH2). Both DFT and electron paramagnetic resonance (EPR) analyses further indicate that, upon T-TET, the triplet wave function is localized on the carotenoid in both dyads.artificial photosynthesis | photoprotection | DFT calculations | triplet-triplet energy transfer | resonance Raman P hotoprotection is central to the maintenance of photosynthesis. Under certain circumstances, chlorophyll excited triplet states may form from intersystem crossing and from electron-hole recombination reactions in reaction centers. Chlorophyll triplet species can sensitize the formation of singlet oxygen, a deleterious reactive oxygen species (1). In photosynthetic complexes, this sensitization reaction is precluded by sufficiently rapid transfer of the triplet excited state from chlorophyll (Chl) or bacteriochlorophyll (BChl) to carotenoid molecules. The triplet states of carotenoids involved in photoprotection are well below the energy of singlet oxygen and therefore do not sensitize singlet oxygen. This quenching reaction reduces the lifetime of the Chl or BChl triplet state by many orders of magnitude (1) and renders it kinetically incompetent to sensitize singlet oxygen. Moreover, carotenoids can quench singlet oxygen directly in the event that it is inadvertently formed.In the light-harvesting (LH) proteins from most (anoxygenic) purple bacteria, triplet-triplet energy transfer (T-TET) from BChl to carotenoid molecules occurs on the nanosecond timescale (2, 3). By contrast, in light-harvesting complexes (LHCs) from...

show abstract

Section: Significancementioning

confidence: 99%

Triplet–triplet energy transfer in artificial and natural photosynthetic antennas

Kish

Méndez-Hernández

et al. 2017

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

Self Cite

View full text Add to dashboard Cite

show abstract

“…Radical cations of carotenoids may be readily formed chemically by the addition of an oxidizing agent (Ioffe et al 1976;Ding et al 1988;Jeevarajan et al 1996;Gao et al 1997;Wei et al 1997;Krawczyk 1998), electrochemically in a cell having a sufficiently positive voltammetric potential Khaled et al 1990;Khaled et al 1991;He and Kispert 1999a;He and Kispert 1999b;Liu and Kispert 1999;Deng et al 2000;Hapiot et al 2001), photochemically upon light absorption in photosynthetic pigment-protein complexes (Schenck et al 1982;Rivas et al 1993;Polívka et al 2004;Holt et al 2005), or in synthetic covalently linked carotenoid donor/electron acceptor molecular systems (Gust and Moore 1991;Gust et al 1993). …”

Section: Introductionmentioning

confidence: 98%

Cation radicals of xanthophylls

et al. 2007

View full text Add to dashboard Cite

Carotenes and xanthophylls are well known to act as electron donors in redox processes. This ability is thought to be associated with the inhibition of oxidative reactions in reaction centers and light-harvesting pigment-protein complexes of photosystem II (PSII). In this work, cation radicals of neoxanthin, violaxanthin, lutein, zeaxanthin, beta-cryptoxanthin, beta-carotene, and lycopene were generated in solution using ferric chloride as an oxidant and then studied by absorption spectroscopy. The investigation provides a view toward understanding the molecular features that determine the spectral properties of cation radicals of carotenoids. The absorption spectral data reveal a shift to longer wavelength with increasing pi-chain length. However, zeaxanthin and beta-cryptoxanthin exhibit cation radical spectra blue-shifted compared to that of beta-carotene, despite all of these molecules having 11 conjugated carbon-carbon double bonds. CIS molecular orbital theory quantum computations interpret this effect as due to the hydroxyl groups in the terminal rings selectively stabilizing the highest occupied molecular orbitals of preferentially populated s-trans-isomers. The data are expected to be useful in the analysis of spectral results from PSII pigment-protein complexes seeking to understand the role of carotene and xanthophyll cation radicals in regulating excited state energy flow, in protecting PSII reaction centers against photoinhibition, and in dissipating excess light energy absorbed by photosynthetic organisms but not used for photosynthesis.

show abstract

“…Key to functionality in such systems is the production of a long-lived charge-separated state that allows the associated chemical potential to be captured. Inspired by the general design of natural photosynthetic reaction centers, a widely used approach has been to slow wasteful charge recombination by using sequential steps to increase hole-electron spatial separation within multicomponent architectures, including tetrapyrrole-based triads and larger arrays (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). For example, in a generic triad of covalently linked redox-active pigments denoted ABC, photoexcitation of B and subsequent excited-state electron transfer to C is followed by a hole shift to A in the sequence AB*C fi AB + C ) fi A + BC ) .…”

Section: Introductionmentioning

confidence: 99%

Probing Ground‐state Hole Transfer Between Equivalent, Electrochemically Inaccessible States in Multiporphyrin Arrays Using Time‐resolved Optical Spectroscopy

Song

Taniguchi

Kirmaier

et al. 2009

Photochem & Photobiology

View full text Add to dashboard Cite

A new strategy is described and implemented for determining the rates of hole-transfer between equivalent porphyrins in multiporphyrin architectures. The approach allows access to these rates between sites that are not the most easily oxidized components of the array. The specific architectures investigated with this new strategy are triads consisting of one zinc porphyrin (Zn) and two free base porphyrins (Fb). The triads employ a diphenylethyne linker (ZnFbFbU) and a phenylene linker (ZnFbFbPhi). The zinc porphyrin is selectively oxidized to produce Zn(+)FbFb, the free base porphyrins are excited to produce the excited-state mixture Zn(+)Fb*Fb and Zn(+)FbFb*, and the subsequent dynamics are monitored by ultrafast absorption spectroscopy. The system evolves by a combination of energy- and hole-transfer processes involving (adjacent and nonadjacent) zinc and free base porphyrin constituents that are complete within 100 ps of excitation; the rate constants of many of these processes are derived from prior studies of the oxidized forms of the benchmark dyads (ZnFbU and ZnFbPhi). One of the excited-state decay channels produces the metastable state ZnFbFb(+) that decays to a second metastable state ZnFb(+)Fb by the target hole-transfer process, followed by rapid hole transfer to produce the Zn(+)FbFb thermodynamic ground state of the system. The rate constant for hole transfer between the free base porphyrins in the oxidized ZnFbFb triads is found to be (0.5 ns)(-1) and (0.6 ns)(-1) across phenylene and diphenylethyne linkers, respectively. These rate constants are comparable to those recently measured, using a related but distinct strategy, for ground-state hole transfer between zinc porphyrins in oxidized ZnZnFb triads. The two complementary strategies provide unique approaches for probing hole transfer between equivalent sites in multiporphyrin arrays, with the choice of method being guided by the particular target process and the ease of synthesis of the necessary architectures.

show abstract

Mimicking Photosynthetic Electron and Energy Transfer

Cited by 100 publications

References 92 publications

Triplet–triplet energy transfer in artificial and natural photosynthetic antennas

Triplet–triplet energy transfer in artificial and natural photosynthetic antennas

Cation radicals of xanthophylls

Probing Ground‐state Hole Transfer Between Equivalent, Electrochemically Inaccessible States in Multiporphyrin Arrays Using Time‐resolved Optical Spectroscopy

Contact Info

Product

Resources

About