Charge separation and energy transfer in carotenopyropheophorbide-quinone triads

Liddell, Paul A.; Barrett, Donna; Makings, Lewis R.; Pessiki, Peter J.; Gust, Devens; Moore, Thomas A.

doi:10.1021/ja00277a053

Cited by 59 publications

(33 citation statements)

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“…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. In the latter, the actual T-TET rate could not be determined because intersystem crossing in the tetrapyrrole is the ratelimiting step (9,10,13). In this work, we have studied two closely related dyads, one exhibiting slow and the other fast T-TET, using a combination of vibrational and transient absorption spectroscopic methods, EPR measurements, and density functional theory (DFT) calculations.…”

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.

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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...

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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.

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“…Liddell et al reported a triad containing a carotinoid-linked pyropheophorbide as the primary electron donor and naphthoquinones as acceptors. 2 Wasielewski and co-workers synthesized a chlorophyll-porphyrin-quinone triad and a long-lived photoinduced charge-separated state exhibiting lifetimes of milliseconds was detected. 3 Lindsey et al have reported the formation of two cofacially linked chlorin quinone cyclophanes, 4 and the synthesis of a diad with a metallochlorin linked to a quinone derivative via theˇ-pyrrole position was published recently by Abel and Montforts.…”

Section: Introductionmentioning

confidence: 99%

EPR and ENDOR of radicals of chlorin- and bacteriochlorin-quinone model compounds for electron transfer in photosynthesis

et al. 2000

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“…This dependence is consistent with the involvement of electron exchange terms in the electronic matrix element coupling the initial and final states. These observations led to the prediction that accessory carotenoid pigments would be found in van der Waals contact with bacteriochlorophylls in the reaction centers of photosynthetic bacteria [58]. Indeed, the crystal structure of wild-type Rb.…”

Section: A Carotenoporphyrinsmentioning

confidence: 99%

“…Again, in order to establish that conclusions can be transferred from porphyrin to chlorophyll-based systems we measured the triplet-triplet energy transfer rate in carotenopyropheophorbide 28 [58]. The rise time of the carotenoid triplet state was faster than the 50ns response time of the spectrometer, and is likely limited by kirc.…”

Section: Triplet-triplet Energy Transfermentioning

confidence: 99%

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Mimicking Photosynthetic Electron and Energy Transfer

Gust

Moore

1991

Advances in Photochemistry

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100

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Charge separation and energy transfer in carotenopyropheophorbide-quinone triads

Cited by 59 publications

References 3 publications

Triplet–triplet energy transfer in artificial and natural photosynthetic antennas

Triplet–triplet energy transfer in artificial and natural photosynthetic antennas

EPR and ENDOR of radicals of chlorin- and bacteriochlorin-quinone model compounds for electron transfer in photosynthesis

Mimicking Photosynthetic Electron and Energy Transfer

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