Quinones as Reversible Electron Relays in Artificial Photosynthesis

Rodenberg, Alexander; Orazietti, Margherita; Mosberger, Mathias; Bachmann, Cyril; Probst, Benjamin; Alberto, Roger; Hamm, Peter

doi:10.1002/cphc.201501085

Cited by 36 publications

(35 citation statements)

References 36 publications

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“…3). [23] This process generates two protons which are included to the rapid disproportionation process (one electron transfer) of two molecules of semiquinone radical-anion to quinone (Q) and H 2 Q. [24] To evaluate the best external bias to be used in the photoelectrochemical measurements, linear sweep voltammetry (LSV) in dark and under irradiation, sweeping from À0.19 to 1.09 V vs RHE, were performed on the differently sensitized photoanodes ( Figure 5).…”

Section: Resultsmentioning

confidence: 99%

Organic Sensitizers for Photoanode Water Splitting in Dye‐Sensitized Photoelectrochemical Cells

2018

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Metal‐free di‐branched organic sensitizers, containing different heteroaromatic (phenothiazine, phenoxazine and carbazole) donor moieties, have been investigated as photoactive anode sensitizers in the photoelectrochemical generation of oxygen and water splitting. Photoelectrochemical properties have been studied both in the presence of a sacrificial electron donor, to closely evaluate the charge‐transfer phenomena and the external quantum efficiency, and with a common water oxidation catalyst, to preliminarily assess the photoelectrochemical water‐splitting activity and oxygen production. The experimental performance trend, in terms of photogenerated charge and evolved gas, was phenothiazine>carbazole>phenoxazine, arising from superior light‐harvesting capability and more efficient electron injection to the semiconductor.

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Section: Resultsmentioning

confidence: 99%

Organic Sensitizers for Photoanode Water Splitting in Dye‐Sensitized Photoelectrochemical Cells

2018

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“…For instance, quantities are strongly influenced even by subtle variations of the different components (e.g., SED, PS, pH, concentrations/ratios, and light source) . There is a great deal of reported information on the initial steps of photocatalysis in homogeneous solutions, that is, the study of the processes that follow excitation of the photosensitizer (reductive/oxidative quenching, first electron transfer to cobalt, and follow‐up reactions of oxidized electron donors), both in organic and aqueous media, as well as in mixtures . There are, from a spectroscopic point of view, only few studies focusing on the follow‐up reactions of the reduced cobalt species in water or organic solvents .…”

Section: Introductionmentioning

confidence: 99%

Structure–Activity and Stability Relationships for Cobalt Polypyridyl‐Based Hydrogen‐Evolving Catalysts in Water

et al. 2017

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A series of eight new and three known cobalt polypyridyl‐based hydrogen‐evolving catalysts (HECs) with distinct electronic and structural differences are benchmarked in photocatalytic runs in water. Methylene‐bridged bis‐bipyridyl is the preferred scaffold, both in terms of stability and rate. For a cobalt complex of the tetradentate methanol‐bridged bispyridyl–bipyridyl complex [CoIIBr(tpy)]Br, a detailed mechanistic picture is obtained by combining electrochemistry, spectroscopy, and photocatalysis. In the acidic branch, a proton‐coupled electron transfer, assigned to formation of CoIII−H, is found upon reduction of CoII, in line with a pKa(CoIII−H) of approximately 7.25. Subsequent reduction (−0.94 V vs. NHE) and protonation close the catalytic cycle. Methoxy substitution on the bipyridyl scaffold results in the expected cathodic shift of the reduction, but fails to change the pKa(CoIII−H). An analysis of the outcome of the benchmarking in view of this postulated mechanism is given along with an outlook for design criteria for new generations of catalysts.

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“…Additionally, their electron acceptor and donor properties can be fine‐tuned by varying the substituent groups on the central ring and by adjusting the properties of their immediate environment, for example through hydrogen bonding interactions in a protein pocket. It is not surprising that these features make quinones attractive also in artificial photosynthesis and in technological applications such as functionalization of materials developed for energy harvesting and storage …”

Section: Introductionmentioning

confidence: 99%

Systematic High‐Accuracy Prediction of Electron Affinities for Biological Quinones

2018

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Quinones play vital roles as electron carriers in fundamental biological processes; therefore, the ability to accurately predict their electron affinities is crucial for understanding their properties and function. The increasing availability of cost-effective implementations of correlated wave function methods for both closed-shell and open-shell systems offers an alternative to density functional theory approaches that have traditionally dominated the field despite their shortcomings. Here, we define a benchmark set of quinones with experimentally available electron affinities and evaluate a range of electronic structure methods, setting a target accuracy of 0.1 eV. Among wave function methods, we test various implementations of coupled cluster (CC) theory, including local pair natural orbital (LPNO) approaches to canonical and parameterized CCSD, the domainbased DLPNO approximation, and the equations-of-motion approach for electron affinities, EA-EOM-CCSD. In addition, several variants of canonical, spin-component-scaled, orbital-optimized, and explicitly correlated (F12) Møller-Plesset perturbation theory are benchmarked. Achieving systematically the target level of accuracy is challenging and a composite scheme that combines canonical CCSD(T) with large basis set LPNObased extrapolation of correlation energy proves to be the most accurate approach. Methods that offer comparable performance are the parameterized LPNO-pCCSD, the DLPNO-CCSD(T 0 ), and the orbital optimized OO-SCS-MP2. Among DFT methods, viable practical alternatives are only the M06 and the double hybrids, but the latter should be employed with caution because of significant basis set sensitivity. A highly accurate yet cost-effective DLPNO-based coupled cluster approach is used to investigate the methoxy conformation effect on the electron affinities of ubiquinones found in photosynthetic bacterial reaction centers.

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Quinones as Reversible Electron Relays in Artificial Photosynthesis

Cited by 36 publications

References 36 publications

Organic Sensitizers for Photoanode Water Splitting in Dye‐Sensitized Photoelectrochemical Cells

Organic Sensitizers for Photoanode Water Splitting in Dye‐Sensitized Photoelectrochemical Cells

Structure–Activity and Stability Relationships for Cobalt Polypyridyl‐Based Hydrogen‐Evolving Catalysts in Water

Systematic High‐Accuracy Prediction of Electron Affinities for Biological Quinones

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