Electron-transfer Fluorescence Quenching of Radical Ions.

Eriksen, Jens; Lund, Henning; Nyvad, Annette I.; Yamato, Takehiko; Mitchell, Reginald H.; Dingle, Thomas W.; Williams, Richard Vaughan; Mahedevan, Ramanathan

doi:10.3891/acta.chem.scand.37b-0459

Cited by 45 publications

(39 citation statements)

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“…Then DCA •– was excited by the green-light region, giving rise to its excited state, DCA •– *, a highly reactive species with an estimated reducing potential of −3.2 V (vs SCE) 60 and a lifetime of 13.5 ns 61 that allowed it to engage in reductive activation of heteroarene halides. In fact, the electron transfer from DCA •– * would be an exergonic process in all cases, and the trend of substrate reactivity was very accurately mirrored by these thermodynamic data ( Table 5 ).…”

Section: Results and Discussionmentioning

confidence: 99%

Highly Efficient Production of Heteroarene Phosphonates by Dichromatic Photoredox Catalysis

Herrera-Luna

Díaz

Jiménez

et al. 2021

ACS Appl. Mater. Interfaces

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A new strategy to achieve efficient aerobic phosphorylation of five-membered heteraroenes with excellent yields using dichromatic photoredox catalysis in a gel-based nanoreactor is described here. The procedure involves visible aerobic irradiation (cold white LEDs) of a mixture containing the heteroarene halide, trisubstituted phospite, N , N -diisopropylethylamine (DIPEA) as sacrificial agent, and catalytic amounts of 9,10-dicyanoanthracene ( DCA ) in the presence of an adequate gelator, which permits a faster process than at the homogeneous phase. The methodology, which operates by a consecutive photoinduced electron transfer (ConPET) mechanism, has been successfully applied to the straightforward and clean synthesis of a number of different heteroarene (furan, thiophene, selenophene, pyrrole, oxazole, or thioxazole) phosphonates, extending to the late-stage phosphonylation of the anticoagulant rivaroxaban. Strategically, employment of cold white light is critical since it provides both selective wavelengths for exciting first DCA (blue region) and subsequently its corresponding radical anion DCA •– (green region). The resultant strongly reducing excited agent DCA •– * is capable of even activate five-membered heteroarene halides (Br, Cl) with high reduction potentials (∼−2.7 V) to effect the C(sp 2 )–P bond formation. Spectroscopic and thermodynamic studies have supported the proposed reaction mechanism. Interestingly, the rate of product formation has been clearly enhanced in gel media because reactants can be presumably localized not only in the solvent pools but also through to the fibers of the viscoelastic gel network. This has been confirmed by field-emission scanning electron microscopy images where a marked densification of the network has been observed, modifying its fibrillary morphology. Finally, rheological measurements have shown the resistance of the gel network to the incorporation of the reactants and the formation of the desired products.

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Section: Results and Discussionmentioning

confidence: 99%

Highly Efficient Production of Heteroarene Phosphonates by Dichromatic Photoredox Catalysis

Herrera-Luna

Díaz

Jiménez

et al. 2021

ACS Appl. Mater. Interfaces

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“…The system in Table , entry 3, does not suffer from the problem of an exceedingly short *PC .− lifetime, because *DCA .− is fluorescent and has a comparatively long excited‐state lifetime of circa 5–10 ns depending on the solvent . Electrolysis at a constant cell voltage permits an essentially quantitative conversion of DCA to DCA .− , making selective PC .− photoexcitation straightforward and leading to an overall monophotonic process.…”

Section: The Next Level: Reductive Excited‐state Quenching Followed Bmentioning

confidence: 99%

Multi‐Photon Excitation in Photoredox Catalysis: Concepts, Applications, Methods

2020

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The energy of visible photons and the accessible redox potentials of common photocatalysts set thermodynamic limits to photochemical reactions that can be driven by traditional visible‐light irradiation. UV excitation can be damaging and induce side reactions, hence visible or even near‐IR light is usually preferable. Thus, photochemistry currently faces two divergent challenges, namely the desire to perform ever more thermodynamically demanding reactions with increasingly lower photon energies. The pooling of two low‐energy photons can address both challenges simultaneously, and whilst multi‐photon spectroscopy is well established, synthetic photoredox chemistry has only recently started to exploit multi‐photon processes on the preparative scale. Herein, we have a critical look at currently developed reactions and mechanistic concepts, discuss pertinent experimental methods, and provide an outlook into possible future developments of this rapidly emerging area.

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“…However, the reaction was prematurely terminated due to the formation of a zinc bridge between the cathode and anode that short-circuited the electrochemical setup (entry 8). Anthraquinone (AQ), which exhibits similar light-induced redox reactivities, 9 was also an effective catalyst, albeit with diminished yield (entry 9). Importantly, this reaction was also applicable to the reductive borylation of 4-chloroanisole (3), which has a highly negative reduction potential (Ered = −2.90 V vs SCE) 15 (entry 10).…”

Section: Figure 1 Electrochemical Generation Of Radical Anionmentioning

confidence: 99%

“…For example, cathodic reduction of dicyanoanthracene (DCA; E1/2 = -0.82 V) results in the corresponding radical anion DCA •-, which absorbs visible light and exhibits a strong fluorescence emission (excitation energy E0,0 = 2.38 eV). 9 The photoexcited DCA (DCA •-*) is estimated to display an exceptionally high reducing potential of -3.2 V (vs. SCE), 10 which TD-DFT calculations suggest arises from a SOMO-HOMO level inversion featuring a very unstable electronic structure with a half-filled bonding orbital (ψ1) and a filled antibonding orbital (ψ2) (see Figure S3 in Supporting Information). Strong reductant…”

mentioning

confidence: 99%

Reductive Electrophotocatalysis: Merging Electricity and Light to Achieve Extreme Reduction Potentials

Kim

Lambert

Lin

2019

Preprint

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We describe a new electrophotocatalytic strategy that harnesses the power of light and electricity to generate an excited radical anion with a reducing potential of –3.2 V vs. SCE, which can be used to activate substrates with very high reduction potentials (Ered ~ –1.9 to –2.9 V). The resultant aryl radicals can be engaged in various synthetically useful transformations to furnish arylboronate, arylstannane, and biaryl products.

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Electron-transfer Fluorescence Quenching of Radical Ions.

Cited by 45 publications

References 0 publications

Highly Efficient Production of Heteroarene Phosphonates by Dichromatic Photoredox Catalysis

Highly Efficient Production of Heteroarene Phosphonates by Dichromatic Photoredox Catalysis

Multi‐Photon Excitation in Photoredox Catalysis: Concepts, Applications, Methods

Reductive Electrophotocatalysis: Merging Electricity and Light to Achieve Extreme Reduction Potentials

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