Singlet oxygen production from singlet and triplet states of 9,10-dicyanoanthracene

Kanner, Richard C.; Foote, Christopher S.

doi:10.1021/ja00028a040

Cited by 55 publications

(61 citation statements)

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“…Based on these observations, the photoreactor was cooled to À20 8C, working at a substrate flow rate of 2 mL min À1 for maximum productivity. The three sensitizers, tetraphenylporphyrin (TPP, singlet-oxygen quantum yield F D = 0.63 in benzene), [19] zinc tetraphenylporphyrin (ZnTPP, F D = 0.83 in benzene), [19] and 9,10-dicyanoanthracene (DCA, F D = 1.56 in benzene), [26] were evaluated at different concentrations. These dyes absorb light at 420 nm.…”

Section: Resultsmentioning

confidence: 99%

A Continuous‐Flow Process for the Synthesis of Artemisinin

Kopetzki

Lévesque

Seeberger

2013

Chemistry A European J

197

190

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Isolation of the most effective antimalarial drug, artemisinin, from the plant sweet wormwood, does not yield sufficient quantities to provide the more than 300 million treatments needed each year. The high prices for the drug are a consequence of the unreliable and often insufficient supply of artemisinin. Large quantities of ineffective fake drugs find a market in Africa. Semisynthesis of artemisinin from inactive biological precursors, either dihydroartemisinic acid (DHAA) or artemisinic acid, offers a potentially attractive route to increase artemisinin production. Conversion of the plant waste product, DHAA, into artemisinin requires use of photochemically generated singlet oxygen at large scale. We met this challenge by developing a one-pot photochemical continuous-flow process for the semisynthesis of artemisinin from DHAA that yields 65 % product. Careful optimization resulted in a process characterized by short residence times. A method to extract DHAA from the mother liquor accumulated during commercial artemisinin extractions, a material that is currently discarded as waste, is also reported. The synthetic continuous-flow process described here is an effective means to supplement the limited availability of artemisinin and ensure increased supplies of the drug for those in need.

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Section: Resultsmentioning

confidence: 99%

A Continuous‐Flow Process for the Synthesis of Artemisinin

Kopetzki

Lévesque

Seeberger

2013

Chemistry A European J

197

190

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“…Gurinovich and Salokhiddinov determined Q Δ for aromatic molecules directly via the O 2 (1Δ g ) emission and found that Q Δ approaches the limit 2 at high O 2 concentrations, if Δ E ST < 94 kJ mol −1 (78). Dobrowolski et al (79), Kanner and Foote (80), and Kristiansen et al (58) used chemical techniques and O 2 (1Δ g ) emission spectroscopy to determine the value of Q Δ ∞ = f s Δ for 9,10‐dicyanoanthracene (DCA) and obtained values between 1.5 and 2 in BNZ, CHX and ACN. Thus, the results of the different investigations agree in the finding that in the reaction of (), O 2 (1Δ g ) generation in the fluorescence quenching by O 2 may be a very important process, particularly for highly fluorescent molecules.…”

Section: Discussionmentioning

confidence: 99%

Photosensitized Generation of Singlet Oxygen

Schmidt

2007

Photochemistry and Photobiology

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This work gives an overview of what is currently known about the mechanisms of the photosensitized production of singlet oxygen. Quenching of ππ* excited triplet states by O2 proceeds via internal conversion of excited encounter complexes and exciplexes of sensitizer and O2. Both deactivation channels lead with different efficiencies to singlet oxygen generation. The balance between the deactivation channels depends on the triplet‐state energy and oxidation potential of the sensitizer, and on the solvent polarity. A model has been developed that reproduces rate constants and efficiencies of the competing processes quantitatively. Sensitization by excited singlet states is much more complex and hence only qualitative rules could be elaborated, despite serious efforts of many groups. However, the most important deactivation paths of fluorescence quenching by O2 are again directed by excess energies and charge‐transfer interactions similar to triplet‐state quenching by O2. Finally, two recent developments in photo‐sensitization of singlet oxygen are reviewed: Two‐photon sensitizers with particular application potential for photodynamic therapy and fluorescence imaging of biological samples and singlet oxygen sensitization by nanocrystalline porous silicon, a material with very different photophysics compared to molecular sensitizers.

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“…It thus emerged that (i) singlet oxygen quantum yields were very high in the silica xerogels, (ii) when grafting the DBTP derivative, DBTP–CO‐NH–(CH 2 ) 6 –NH 2 on silica , Φ ∆ decreased from 1.03 to 0.6, (iii) a strong increase in Φ ∆ was obtained for DCA on going from ACN solutions to SG0 monoliths, which may be related to the different oxygen concentration in the two media. Indeed, singlet oxygen quantum yields of DCA have been reported to be dependent on oxygen concentration due to its peculiar ability to produce singlet oxygen directly from its singlet state by oxygen‐enhanced ISC . In any case, DBTP and even AQ appeared to be much better singlet oxygen sensitizers than DCA in air‐equilibrated ACN solution under our conditions.…”

Section: Resultsmentioning

confidence: 60%

“…Considering the properties of the PSs, it is worth recalling that DCA is known to produce singlet oxygen either directly from its singlet state or by oxygen‐enhanced ISC from its singlet state, accounting for the high sensitivity of the published singlet quantum yields to oxygen concentration and possible explanation of the much higher Φ ∆ in silica monoliths (1.02) than in ACN (0.31). On the contrary, AQ and DBTP are characterized by an extremely efficient ISC ( Φ T 0.9 and 0.85 ) and their photosensitizing activity is exclusively related to their triplet states.…”

Section: Discussionmentioning

confidence: 99%

Immobilized Organic Photosensitizers with Versatile Reactivity for Various Visible‐Light Applications

Ronzani

Saint‐Cricq

Arzoumanian

et al. 2013

Photochem & Photobiology

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Various photosensitizers were grafted by conventional peptide coupling methods to functionalized silica with several macroscopic shapes (powders, films) or embedded in highly transparent and microporous silica xerogel monoliths. Owing to the transparency and free-standing shape of the monoliths, the transient species arising from irradiation of the PSs could be analyzed and were not strikingly different from those observed in solutions. The observed reactivity for either liquid-solid (α-terpinene oxygenation vs dehydrogenation) or gas-solid (dimethylsulfide, DMS, solvent-free oxidation) reactions was consistent with the properties of the excited states of the PSs under consideration. Immobilized anthraquinone-derived materials preferentially react in both cases by electron transfer from the substrate to the triplet state of the sensitizer, in spite of an efficient singlet oxygen production. The recently developed 9,14-dicyanobenzo[b]triphenylene-3-carboxylic acid, DBTP-COOH, efficiently reacts via energy transfer to yield singlet oxygen from its triplet state. It was shown to perform better than 9,10-dicyanoanthracene and rose bengal for DMS oxidation and α-terpinene photooxygenation to ascaridole, respectively. Thus, by a proper choice of the organic immobilized photocatalyst, it is possible to develop efficient and reusable materials, activated under visible light, for various applications and to tune the reaction pathway, opening the way to green oxidation processes.

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Singlet oxygen production from singlet and triplet states of 9,10-dicyanoanthracene

Cited by 55 publications

References 0 publications

A Continuous‐Flow Process for the Synthesis of Artemisinin

A Continuous‐Flow Process for the Synthesis of Artemisinin

Photosensitized Generation of Singlet Oxygen

Immobilized Organic Photosensitizers with Versatile Reactivity for Various Visible‐Light Applications

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