Effect of exothermicity on electron transfer rates in photosynthetic molecular models

Joran, A. D.; Leland, Burt A.; Felker, Peter; Zewail, A. H.; Hopfield, J. J.; Dervan, Peter B.

doi:10.1038/327508a0

Cited by 159 publications

(53 citation statements)

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“…A study of photoinduced electron transfer in porphyrin-quinone systems carried out in butyronitrile solution yielded a value for ! of 1.25 eV [32]. Using this value and values for k 4 and DG 0 of 2.0 Â 10 11 s À1 and À0.28 eV respectively for triad 1 at 298 K, equation (5) yields V = 1150 cm À1 for step 4 in triad 1.…”

Section: Effect Of Driving Force On Quantum Yieldmentioning

confidence: 92%

Increasing the Yield of Photoinduced Charge Separation through Parallel Electron Transfer Pathways

Maniga

Sumida

Stone

et al. 1999

J. Porphyrins Phthalocyanines

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A strategy for increasing the yield of long-lived photoinduced charge separation in artificial photosynthetic reaction centers which is based on multiple electron transfer pathways operating in parallel has been investigated. Excitation of the porphyrin moiety of a carotenoid ( C )–porphyrin ( P )–naphthoquinone (Q) molecular triad leads to the formation of a charge-separated state C ·+– P – Q ·− with an overall quantum yield of 0.044 in benzonitrile solution. Photoinduced electron transfer from the porphyrin first excited singlet state gives C – P ·+– Q ·− with a quantum yield of ~1.0. However, electron transfer from the carotenoid to the porphyrin radical cation to form the final state does not compete well with charge recombination of C – P ·+– Q ·−, reducing the yield. The related pentad C 3– P – Q features carotenoid, porphyrin and quinone moieties closely related to those in the triad. Excitation of this molecule gives a C ·+– P ( C 2)– Q ·− state with a quantum yield of 0.073. The enhanced yield is ascribed to the fact that three electron donation pathways operating in parallel compete with charge recombination. The yield does not increase by the statistically predicted factor of three owing to small differences in thermodynamic driving force between the two compounds.

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Section: Effect Of Driving Force On Quantum Yieldmentioning

confidence: 92%

Increasing the Yield of Photoinduced Charge Separation through Parallel Electron Transfer Pathways

Maniga

Sumida

Stone

et al. 1999

J. Porphyrins Phthalocyanines

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“…This procedure was repeated twice whereupon the supernatant was colorless. The resulting solid was dried in vacuo, affording a crystalline orange-purple solid (0.064 g, 93%): 1 NiSWTP. A solution of free base meso-tetrakis(tridec-7-yl)-porphyrin (H 2 SWTP, 0.035 g, 0.033 mmol) in CHCl 3 (10 mL) was treated with a solution of Ni(OAc) 2 ‚4H 2 O (0.167 g, 0.672 mmol) in CH 3 OH (1 mL).…”

Section: Choice Of Compounds and Preparationmentioning

confidence: 99%

Ultrafast Stimulated Emission and Structural Dynamics in Nickel Porphyrins

et al. 2007

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The excited-state structural dynamics of nickel(II)tetrakis(2,4,6-trimethylphenyl)porphyrin (NiTMP) and nickel(II)tetrakis(tridec-7-yl)porphyrin (NiSWTP) in a toluene solution were investigated via ultrafast transient optical absorption spectroscopy. An ultrashort stimulated emission between 620 and 670 nm from the S1 state was observed in both nickel porphyrins only when this state was directly generated via Q-band excitation, whereas such a stimulated emission was absent under B (Soret)-band excitation. Because the stimulated emission in the spectral region occurs only from the S1 state, this photoexcitation-wavelength-dependent behavior of Ni(II) porphyrins is attributed to a faster intersystem crossing from the S2 state than the internal conversion S2 --> S1. The dynamics of the excited-state pathways involving the (pi, pi*) and (d, d) states varies with the meso-substituted peripheral groups, which is attributed to the nickel porphyrin macrocycle distortion from a planar configuration. Evidence for intramolecular vibrational relaxation within 2 ps and vibrational cooling in 6-20 ps of a (d, d) excited state has been established for NiTMP and NiSWTP. Finally, the lifetimes of the vibrationally relaxed (d, d) state also depend on the nature of the peripheral groups, decreasing from 200 ps for NiTMP to 100 ps for the bulkier NiSWTP.

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“…This would not significantly alter the dynamical properties of the system, leaving the present analysis valid. [2,32] In this work, we assume ∆E v = 0, which amounts to modeling a barrierless ET process with a driving force −∆E • = λ Q +λ P of about 0.5 eV. This assumption, albeit ad hoc, has a sound physical basis, as barrierless ETs have been widely documented in porphyrin-quinone type complexes.…”

Section: Model Parametersmentioning

confidence: 99%

First-principles study of photoinduced electron-transfer dynamics in a Mg–porphyrin–quinone complex

Borrelli

Domcke

2010

Chemical Physics Letters

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The photoinduced electron-transfer process between a magnesium-porphyrin and a quinone in a model complex has been studied by means of quantum dynamical methods. The microscopic parameters controlling the electrontransfer process have been obtained using ab initio electronic structure calculations. A quantum dynamical simulation for a reduced dimensionality model, including only the totally symmetric vibrational degrees of freedom of the quinone molecule, shows that the electron-transfer is fast, taking place in a few hundreds of femtoseconds, in agreement with experimental results for similar systems.

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Effect of exothermicity on electron transfer rates in photosynthetic molecular models

Cited by 159 publications

References 0 publications

Increasing the Yield of Photoinduced Charge Separation through Parallel Electron Transfer Pathways

Increasing the Yield of Photoinduced Charge Separation through Parallel Electron Transfer Pathways

Ultrafast Stimulated Emission and Structural Dynamics in Nickel Porphyrins

First-principles study of photoinduced electron-transfer dynamics in a Mg–porphyrin–quinone complex

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