Photoreduction of tetraphenylporphyrins by amines in the visible. Photochemical syntheses of reduced tetraphenylporphyrins and the mechanism of photoreduction

Harel, Yaacov; Manassen, J.

doi:10.1021/ja00487a047

Cited by 40 publications

(18 citation statements)

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“…52,55 Additionally, bacteriochlorin has the Q-band absorption at about 760 nm, 111,112 although isobacteriochlorin should be preferably formed instead of bacteriochlorin and should be stable to oxygenation. 100 A new peak at 446 nm and a broad band of absorbance between 700 and 900 nm (with possible maxima at about 660, 720, 760, and 820) were observed, especially at pH 9.0 (Figure 9B). These spectral features were previously attributed to π-radical anion and/or phlorin by different authors or overlapping of the spectral features of these species.…”

Section: Resultsmentioning

confidence: 99%

“…An additional factor contributing to the photochemical reaction mechanism and efficiency of the porphyrin series might be the formation of associates between the porphyrin molecules and EDTA either before or during excitation, as the studies on the association of porphyrin molecules by hydrogen bonds or electrostatic interactions between reactants suggest. − A closer contact and association of the electron donor EDTA and Sn(IV)P might then favor the formation and/or stabilization of the π-radical anion during irradiation. In this case, e.g., in alkaline and neutral media (pH 7.4 and 9.0), the interaction of SnTPyP (p K a (Py) = 5.2) with EDTA as HY 3– (four carboxyl groups and one amine are deprotonated, while one amine is protonated, p K 1 (CO 2 H) = 0.0, p K 2 (CO 2 H) = 1.5, p K 3 (CO 2 H) = 2.0, p K 4 (CO 2 H) = 2.7, p K 5 (NH + ) = 6.1, p K 6 (NH + ) = 10.4) would be more favorable than with the negatively charged SnTPPC or SnTPPS (p K a (benzenesulfonic acid) = 2.6, p K a (benzenecarboxylic acid) = 4.2).…”

Section: Resultsmentioning

confidence: 99%

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Influence of Meso-Substitution of the Porphyrin Ring on Enhanced Hydrogen Evolution in a Photochemical System

et al. 2016

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This study establishes the relationships between the structure of a series of meso-substituted tin(IV) porphyrins and their efficiency as photosensitizers for hydrogen generation in the Sn(IV)P/Pt–TiO2 nanocomposite system. The electrochemical properties of a series of SnPs, the catalytic performance of Pt nanomodifications, and the morphology of the Pt/TiO2 nanocomposites were characterized by electrochemical and electron microscopy methods. The dependence of photocatalytic performance on the structure for a series of Sn(IV) meso-substituted phenyl porphyrins was studied, and possible mechanisms are discussed employing the results of the electrochemical studies. It was found that the time course and type of the photochemically reduced species of Sn(IV)Ps, which are essential intermediates, are important factors and depend on the electronegativity of the metal center, the character of meso-substituents of the porphyrin ring, and pH and are correlated with the redox potential sequence of the respective Sn(IV)Ps: SnTMPyP > SnTPyP > SnTPPS > SnTPPC. Optimization of the experimental parameters was performed with regard to the SnPs with different functional groups, pH values, concentrations of Pt/TiO2, light intensity, and Pt nanoparticles with different surface stabilizers. Finally, the maximum hydrogen yield under visible light was obtained from the system of Sn(IV) meso-tetra(4-pyridyl)porphyrin dichloride (SnTPyP) sensitized TiO2/Pt prepared by the citrate method/EDTA at pH 9.0. This demonstrates that the photochemically reduced species of SnTPyP are relatively long lived, so they have enough time to complete electron transfer to TiO2 and/or Pt. The adsorption of SnTPyP on the TiO2/Pt surface is therefore not essential for hydrogen generation. Moreover, this study demonstrates for the first time the synergic effect of the excitation of TiO2 and mostly Q-bands of Sn(IV)P (wavelength range 390–650 nm), which enhances the efficiency of photocatalytic hydrogen generation in the system. The Soret band of Sn(IV)TPyP was found to produce a minor (about 23%) contribution to the photocatalytic activity of the porphyrin sensitizer in this system. Possible processes involved are discussed, and mechanisms are proposed explaining different aspects of a series of photocatalytic systems with SnPs and Pt catalysts for hydrogen production under visible light. These structure–function relationships are essential to effectively harness solar energy for hydrogen production as well as for a wide range of energy and environmentally related problems.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Influence of Meso-Substitution of the Porphyrin Ring on Enhanced Hydrogen Evolution in a Photochemical System

et al. 2016

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“…It has been shown previously that triethylamine can add to the pyrrole to form both the simple hydrogenation product and a product in which a C–H bond has been formally added across the C C bond. 95 A large-scale (50 mg) photolysis ( λ > 520 nm) was performed on ZnTPP in DMF : TEOA 5 : 1 under Ar and the product was exhaustively extracted into ether after addition of water. The ether was separated and the product dried under vacuum.…”

Section: Resultsmentioning

confidence: 99%

Comparison of rhenium–porphyrin dyads for CO₂photoreduction: photocatalytic studies and charge separation dynamics studied by time-resolved IR spectroscopy

et al. 2015

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“…Indeed, the saturation of one pyrrole ring by hydrogenation is confirmed by NMR spectroscopy. 28 On prolonged photolysis (100 min, Dyad 1, higher intensity lamp), the system was bleached completely.…”

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confidence: 99%

CO2 photoreduction with long-wavelength light: dyads and monomers of zinc porphyrin and rhenium bipyridine

et al. 2012

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Photoreduction of tetraphenylporphyrins by amines in the visible. Photochemical syntheses of reduced tetraphenylporphyrins and the mechanism of photoreduction

Cited by 40 publications

References 10 publications

Influence of Meso-Substitution of the Porphyrin Ring on Enhanced Hydrogen Evolution in a Photochemical System

Influence of Meso-Substitution of the Porphyrin Ring on Enhanced Hydrogen Evolution in a Photochemical System

Comparison of rhenium–porphyrin dyads for CO₂photoreduction: photocatalytic studies and charge separation dynamics studied by time-resolved IR spectroscopy

CO2 photoreduction with long-wavelength light: dyads and monomers of zinc porphyrin and rhenium bipyridine

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Photoreduction of tetraphenylporphyrins by amines in the visible. Photochemical syntheses of reduced tetraphenylporphyrins and the mechanism of photoreduction

Cited by 40 publications

References 10 publications

Influence of Meso-Substitution of the Porphyrin Ring on Enhanced Hydrogen Evolution in a Photochemical System

Influence of Meso-Substitution of the Porphyrin Ring on Enhanced Hydrogen Evolution in a Photochemical System

Comparison of rhenium–porphyrin dyads for CO2photoreduction: photocatalytic studies and charge separation dynamics studied by time-resolved IR spectroscopy

CO2 photoreduction with long-wavelength light: dyads and monomers of zinc porphyrin and rhenium bipyridine

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Product

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Comparison of rhenium–porphyrin dyads for CO₂photoreduction: photocatalytic studies and charge separation dynamics studied by time-resolved IR spectroscopy