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Schmalzbauer M, Marcon M, König B. Excited State Anions in Organic Transformations. Angew Chem Int Ed Engl 2021; 60:6270-6292. [PMID: 33002265 PMCID: PMC7986118 DOI: 10.1002/anie.202009288] [Citation(s) in RCA: 58] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 09/17/2020] [Indexed: 02/06/2023]
Abstract
Utilizing light is a smart way to fuel chemical transformations as it allows the energy to be selectively focused on certain molecules. Many reactions involving electronically excited species proceed via open-shell intermediates, which offer novel and unique routes to expand the hitherto used synthetic toolbox in organic chemistry. The direct conversion of non-prefunctionalized, less activated compounds is a highly desirable goal to pave the way towards more sustainable and atom-economic chemical processes. Photoexcited closed-shell anions have been shown to reach extreme potentials in single electron transfer reactions and reveal unusual excited-state reactivity. It is, therefore, surprising that their use as a reagent or photocatalyst is limited to a few examples. In this Review, we briefly discuss the characteristics of anionic photochemistry, highlight pioneering work, and show recent progress which has been made by utilizing photoexcited anionic species in organic synthesis.
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Affiliation(s)
- Matthias Schmalzbauer
- Faculty of Chemistry and PharmacyUniversity of RegensburgUniversitätsstrasse 3193053RegensburgGermany
| | - Michela Marcon
- Faculty of Chemistry and PharmacyUniversity of RegensburgUniversitätsstrasse 3193053RegensburgGermany
| | - Burkhard König
- Faculty of Chemistry and PharmacyUniversity of RegensburgUniversitätsstrasse 3193053RegensburgGermany
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Schmalzbauer M, Marcon M, König B. Photoangeregte Anionen in organischen Reaktionen. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202009288] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Matthias Schmalzbauer
- Fakultät für Chemie und Pharmazie Universität Regensburg Universitätsstraße 31 93053 Regensburg Deutschland
| | - Michela Marcon
- Fakultät für Chemie und Pharmazie Universität Regensburg Universitätsstraße 31 93053 Regensburg Deutschland
| | - Burkhard König
- Fakultät für Chemie und Pharmazie Universität Regensburg Universitätsstraße 31 93053 Regensburg Deutschland
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Mandigma MJP, Domański M, Barham JP. C-Alkylation of alkali metal carbanions with olefins. Org Biomol Chem 2020; 18:7697-7723. [PMID: 32785363 DOI: 10.1039/d0ob01180k] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
C-Alkylations of alkali metal carbanions with olefins, first reported five decades ago, is a class of reaction undergoing a resurgence in organic synthesis in recent years. As opposed to expectations from classical chemistry and transition metal-catalysis, here olefins behave as closed-shell electrophiles. Reactions range from highly reactive alkyllithiums giving rise to anionic polymerization, to moderately reactive alkylpotassium or alkylsodium compounds that give rise to defined, controlled and bimolecular chemistry. This review presents a brief historical overview on C-alkylation of alkali metal carbanions with olefins (typically mediated by KOtBu and KHMDS), highlights contemporary applications and features developing mechanistic understanding, thereby serving as a platform for future studies and the widespread use of this class of reaction in organic synthesis.
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Affiliation(s)
- Mark John P Mandigma
- Universität Regensburg, Fakultät für Chemie und Pharmazie, 93040 Regensburg, Germany.
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Shi Y, Zhu K, Dai Y, Zhang C, Jia H. Evolution and stabilization of environmental persistent free radicals during the decomposition of lignin by laccase. CHEMOSPHERE 2020; 248:125931. [PMID: 32000035 DOI: 10.1016/j.chemosphere.2020.125931] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 01/09/2020] [Accepted: 01/14/2020] [Indexed: 05/28/2023]
Abstract
Soil microbial enzymes may induce lignin decomposition, accompanied by generation of free radicals. The evolution of environmentally persistent free radicals (EPFRs) and reactive oxygen species (ROS) during laccase-catalyzed lignin decomposition remains unclear. Characterization by electron paramagnetic resonance spectroscopy revealed gradually increased concentration of EPFRs, with maximum levels within 6 h that remained constant, accompanied by the increase in g-factor from 2.0037 to 2.0041. The results suggested the generation of oxygen-centered radicals on lignin. The EPFRs produced on solid samples slowly decreased by 17.2% over 17 d. ROS were also detected to have a similar trend as that of the evolution of EPFRs. Scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, gel permeation chromatography and nuclear magnetic resonance analyses suggested the demethylation and oxidation of lignin. We clarify the biogeochemical transformation of lignin and potential contributions to the generation of EPFRs and ROS in soil.
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Affiliation(s)
- Yafang Shi
- College of Natural Resources and Environment, Northwest A & F University, Yangling, 712100, China
| | - Kecheng Zhu
- College of Natural Resources and Environment, Northwest A & F University, Yangling, 712100, China
| | - Yunchao Dai
- College of Natural Resources and Environment, Northwest A & F University, Yangling, 712100, China
| | - Chi Zhang
- College of Natural Resources and Environment, Northwest A & F University, Yangling, 712100, China
| | - Hanzhong Jia
- College of Natural Resources and Environment, Northwest A & F University, Yangling, 712100, China; State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation, Northwest A & F University, Yangling, 712100, China.
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Discovery and characterization of an acridine radical photoreductant. Nature 2020; 580:76-80. [PMID: 32238940 PMCID: PMC7138348 DOI: 10.1038/s41586-020-2131-1] [Citation(s) in RCA: 213] [Impact Index Per Article: 53.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Accepted: 02/18/2020] [Indexed: 11/12/2022]
Abstract
Photoinduced electron transfer (PET) is a phenomenon wherein the absorption of light by a chemical species provides an energetic driving force for an electron transfer reaction.1–4 This mechanism is relevant in many areas of chemistry, including the study of natural and artificial photosynthesis, photovoltaics, and photosensitive materials. In recent years, research in the area of photoredox catalysis has leveraged PET for the catalytic generation of both neutral and charged organic free radical species. These technologies have enabled a wide range of previously inaccessible chemical transformations and have seen widespread utilization in both academic and industrial settings. These reactions are often catalyzed by visible-light absorbing organic molecules or transition-metal complexes of ruthenium, iridium, chromium, or copper.5,6 While a wide variety of closed shell organic molecules have been shown to behave as competent electron transfer catalysts in photoredox reactions, there are only limited reports of PET reactions involving neutral organic radicals as an excited state donor or acceptor. This is perhaps somewhat unsurprising in light of previously reported doublet excited state lifetimes for neutral organic radicals, which are typically several orders of magnitude shorter than singlet lifetimes for known transition metal photoredox catalysts.7–11 Herein we document the discovery, characterization, and reactivity of a neutral acridine radical with a maximum excited state oxidation potential of −3.36 V vs. SCE: significantly more reducing than elemental lithium and marking it as one of the most potent chemical reductants reported.12 Spectroscopic, computational, and chemical studies indicate that the formation of a twisted intramolecular charge transfer species enables the population of higher energy doublet excited states, leading to the observed potent photoreductant behavior. We demonstrate that this catalytically-generated PET catalyst facilitates several chemical reactions that typically require alkali metal reductants and bodes well for the adoption of this system in additional organic transformations requiring dissolving metal reductants.
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Cyr D, Das P. Quenching of diphenylmethyl radical fluorescence by cyanoaromatics and phenols. RESEARCH ON CHEMICAL INTERMEDIATES 2015. [DOI: 10.1007/s11164-014-1914-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Spin-enhanced organic bulk heterojunction photovoltaic solar cells. Nat Commun 2012; 3:1043. [DOI: 10.1038/ncomms2057] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2012] [Accepted: 07/30/2012] [Indexed: 11/08/2022] Open
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Grilj J, Zonca C, Daku LML, Vauthey E. Photophysics of the galvinoxyl free radical revisited. Phys Chem Chem Phys 2012; 14:6352-8. [DOI: 10.1039/c2cp23577c] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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BANERJEE SANGHAMITRA, SAMANTA ANUNAY. Laser flash photolysis study on 9-phenylxanthenium tetrafluoroborate: Identification of new features due to the triplet state. J CHEM SCI 2011. [DOI: 10.1007/s12039-011-0070-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Grampp G, Justinek M, Landgraf S, Angulo G, Lukzen N. Viscosity dependence of rubrene fluorescence quenching by organic radicals via energy transfer. Photochem Photobiol Sci 2009; 8:1595-602. [DOI: 10.1039/b902433f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Kawai A, Shibuya K. Charge-Transfer Controlled Exchange Interaction in Radical-Triplet Encounter Pairs as Studied by FT-EPR Spectroscopy. J Phys Chem A 2007; 111:4890-901. [PMID: 17518447 DOI: 10.1021/jp067753d] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The exchange interaction, J, producing quartet and doublet energy separation in radical-triplet excited molecule encounter pairs, was investigated in solution by measuring chemically induced dynamic electron polarization (CIDEP) created through the radical-triplet pair mechanism. A time-resolved FT-EPR method was utilized to measure CIDEP of galvinoxyl radical by recording FID signals and an absolute magnitude of CIDEP, P(n), was determined for each radical-triplet system by detailed analysis of the time evolution curves of CIDEP. A transient FT-EPR signal phase remarkably depends on the triplet molecule. The signal phase is related to the sign of J value, which is responsible for the radical-triplet pair interaction. Most of galvinoxyl-triplet systems showed normal negative sign. An unusual positive sign was found in some systems characterized by a small energy gap, DeltaG, between the radical-triplet pair and intermolecular charge transfer (CT) states. A theoretical calculation of J value for radical-triplet encounter pairs was carried out by considering exchange integral and intermolecular CT interaction. According to the calculated J value and the diffusion theory for CIDEP magnitude, experimental Pn values were theoretically reproduced as a function of DeltaG. The present results confirm our previously reported CT model explaining the complicated nature of the sign of J value in the galvinoxyl-triplet encounter pairs. According to the proposed model for CT effect on J value and CIDEP results, nature of J value in radical-triplet pairs is discussed.
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Affiliation(s)
- Akio Kawai
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ohokayama, Tokyo 152-8551, Japan.
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Sakamoto M, Cai X, Kim SS, Fujitsuka M, Majima T. Intermolecular Electron Transfer from Excited Benzophenone Ketyl Radical. J Phys Chem A 2006; 111:223-9. [PMID: 17214457 DOI: 10.1021/jp064718y] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The electron transfer from the benzophenone ketyl radical in the excited state (BPH(.-)(D(1))) to several quenchers (Qs) was investigated using nanosecond/picosecond two-color two-laser flash photolysis and nanosecond/nanosecond two-color two-laser flash photolysis. The electron transfer from BPH(.-)(D(1)) to Qs was confirmed by the transient absorption and fluorescence quenching measurements. The intermolecular electron-transfer rate constants were determined using the Stern-Volmer analysis. The driving force dependence of the electron-transfer rate was revealed.
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Affiliation(s)
- Masanori Sakamoto
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
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Terazono H, Kawai A, Tsuji K, Shibuya K. Enhanced intersystem crossings of S1–T1 and T1–S0 in coronene– and pyrene–galvinoxyl systems as studied by a pulsed ESR method. J Photochem Photobiol A Chem 2006. [DOI: 10.1016/j.jphotochem.2006.02.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Sakamoto M, Cai X, Fujitsuka M, Majima T. Dual Electron Transfer Pathways from 4,4‘-Dimethoxybenzophenone Ketyl Radical in the Excited State to Parent Molecule in the Ground State. J Phys Chem A 2005; 109:6830-5. [PMID: 16834038 DOI: 10.1021/jp052784e] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Dual intermolecular electron transfer (ELT) pathways from 4,4'-dimethoxybenzophenone (1) ketyl radical (1H*) in the excited state [1H*(D1)] to the ground-state 4,4'-dimethoxybenzophenone [1(S0)] were found in 2-methyltetrahydrofuran (MTHF) by observing bis(4-methoxyphenyl)methanol cation (1H+) and 4,4'-dimethoxybenzophenone radical anion (1*-) during nanosecond-picosecond two-color two-laser flash photolysis. ELT pathway I involved the two-photon ionization of 1H* following the injection of electron to the solvent. The solvated electron was quickly trapped by 1(S0) to produce 1*-. ELT pathway II was a self-quenching-like ELT from 1H*(D1) to 1(S0) to give 1H+ and 1*-. From the fluorescence quenching of 1H*(D1), the ELT rate constant was determined to be 1.0 x 10(10) M(-1) s(-1), which is close to the diffusion-controlled rate constant of MTHF. The self-quenching-like ELT mechanism was discussed on the basis of Marcus' ELT theory.
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Affiliation(s)
- Masanori Sakamoto
- The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
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Mitsui M, Kobori Y, Kawai A, Obi K. Quenching Mechanism of Excited Coronene by a Nitroxide Radical Studied by Probing Dynamic Electron Polarization. J Phys Chem A 2004. [DOI: 10.1021/jp036685h] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Masaaki Mitsui
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro-ku, Tokyo 152-8551, Japan
| | - Yasuhiro Kobori
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro-ku, Tokyo 152-8551, Japan
| | - Akio Kawai
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro-ku, Tokyo 152-8551, Japan
| | - Kinichi Obi
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro-ku, Tokyo 152-8551, Japan
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Kawai A, Watanabe Y, Shibuya K. Control of ferromagnetic and antiferromagnetic couplings in a galvinoxyl–triplet chrysene encounter complex through solvent polarity. Chem Phys Lett 2003. [DOI: 10.1016/s0009-2614(03)00321-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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KAWAI AKIO, WATANABE YASUYUKI, SHIBUYA KAZUHIKO. Time resolved ESR study on energy difference of quartet and doublet states in radical-triplet encounter pairs. Mol Phys 2002. [DOI: 10.1080/00268970110112417] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Parkhomyuk-Ben Arye P, Strashnikova N, Likhtenshtein GI. Stilbene photochrome-fluorescence-spin molecules: covalent immobilization on silica plate and applications as redox and viscosity probes. JOURNAL OF BIOCHEMICAL AND BIOPHYSICAL METHODS 2002; 51:1-15. [PMID: 11879915 DOI: 10.1016/s0165-022x(01)00234-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report herein on the development of a new photochrome-fluorescence-spin method for the quantitative analysis of the redox status and viscosity of a medium. The method of the viscosity measurement is based on the use of double fluorescence-nitroxide molecules. In such hybrid compounds the nitroxide moiety quenches the fluorescence of the fluorophore (stilbene moiety). The reduction of nitroxide by an antioxidant (ascorbic acid) causes a rise of fluorescence of the fluorophore. The rate constant of the stilbene fragment photoisomerization in such systems is dependent upon the viscosity of the media. The synthesized dual stilbene-nitroxide probe was covalently immobilized onto the surface of a quartz plate as an eventual fiber-optic sensor. The immobilization procedure included a cyanogen bromide surface activation followed by smoothing with a protein tether. The rate of fluorescence change was monitored in aqueous-glycerol solutions of different viscosities and content of ascorbic acid. Good correlation was found: (a) between the concentration of ascorbic acid in the sample and the rate of fluorescence increase due to the reduction of the nitroxide moiety, and (b) between the rate constant of photoisomerization and the viscosity of the media. Appropriate calibration would make the determination of the viscosity of a media possible (in a range 1-500 cP), as well as ascorbate content, in a range (1-9) x 10(-4) M, with fast single measurement.
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Affiliation(s)
- P Parkhomyuk-Ben Arye
- Department of Chemistry, Ben-Gurion University of the Negev, P.O.B. 653, Beersheba 84105, Israel.
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Kawai A, Shikama A, Mitsui M, Obi K. Time Resolved ESR Study on the Photochemical Reactions of Pyrene and Nitroxide Radical System in Micelle; Formation of Spin-Correlated Pyrene Cation–Nitroxide Pairs. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2001. [DOI: 10.1246/bcsj.74.1203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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An investigation of the triplet state properties of 1,8-naphthalimide: a laser flash photolysis study. J Photochem Photobiol A Chem 1996. [DOI: 10.1016/s1010-6030(96)04392-4] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Suzuki T, Obi K. Evidence for enhanced intersystem crossing on pyrene fluorescence quenching with stable free radicals. Chem Phys Lett 1995. [DOI: 10.1016/0009-2614(95)01138-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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