1
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Wong SY, Benjamin P, Hore PJ. Magnetic field effects on radical pair reactions: estimation of B1/2 for flavin-tryptophan radical pairs in cryptochromes. Phys Chem Chem Phys 2023; 25:975-982. [PMID: 36519379 PMCID: PMC9811481 DOI: 10.1039/d2cp03793a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Magnetic field effects on the yields of radical pair reactions are often characterised by the "half-field" parameter, B1/2, which encodes useful information on spin relaxation, radical recombination kinetics and electron-electron couplings as well as electron-nuclear hyperfine interactions. Here we use a variety of spin dynamics simulation methods to estimate the hyperfine-only values of B1/2 for the flavin-tryptophan radical pair, [FAD˙- TrpH˙+], thought to be the detector in the magnetic compass sense of migratory songbirds. The main findings are: (a) in the absence of fast recombination and spin relaxation, [FAD˙- TrpH˙+] radical pairs in solution and in the putative magnetoreceptor protein, cryptochrome, have B1/2 ≈ 1.89 mT and 2.46 mT, respectively. (b) The widely used expression for B1/2 due to Weller et al. (Chem. Phys. Lett, 1983, 96, 24-27) is only applicable to small, short-lived (∼5 ns), rapidly tumbling radical pairs in solution, and is quantitatively unreliable in the context of magnetoreception. (c) In the absence of molecular tumbling, the low-field effect for [FAD˙- TrpH˙+] is predicted to be abolished by the anisotropic components of the hyperfine interactions. Armed with the 2.46 mT "base value" for cryptochrome, measurements of B1/2 can be used to understand the impact of spin relaxation on its performance as a magnetic compass sensor.
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Affiliation(s)
- Siu Ying Wong
- Institut für Physik, Carl-von-Ossietzky Universität OldenburgOldenburg 26111Germany
| | - Philip Benjamin
- Department of Chemistry, University of OxfordOxfordOX1 3QZUK
| | - P. J. Hore
- Department of Chemistry, University of OxfordOxfordOX1 3QZUK
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2
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Stass DV. Geometrization for Energy Levels of Isotropic Hyperfine Hamiltonian Block and Related Central Spin Problems for an Arbitrarily Complex Set of Spin-1/2 Nuclei. Int J Mol Sci 2022; 23:15199. [PMID: 36499535 PMCID: PMC9739289 DOI: 10.3390/ijms232315199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 11/20/2022] [Accepted: 11/29/2022] [Indexed: 12/12/2022] Open
Abstract
Description of interacting spin systems relies on understanding the spectral properties of the corresponding spin Hamiltonians. However, the eigenvalue problems arising here lead to algebraic problems too complex to be analytically tractable. This is already the case for the simplest nontrivial (Kmax−1) block for an isotropic hyperfine Hamiltonian for a radical with spin-12 nuclei, where n nuclei produce an n-th order algebraic equation with n independent parameters. Systems described by such blocks are now physically realizable, e.g., as radicals or radical pairs with polarized nuclear spins, appear as closed subensembles in more general radical settings, and have numerous counterparts in related central spin problems. We provide a simple geometrization of energy levels in this case: given n spin-12 nuclei with arbitrary positive couplings ai, take an n-dimensional hyper-ellipsoid with semiaxes ai, stretch it by a factor of n+1 along the spatial diagonal (1, 1, …, 1), read off the semiaxes of thus produced new hyper-ellipsoid qi, augment the set {qi} with q0=0, and obtain the sought n+1 energies as Ek=−12qk2+14∑iai. This procedure provides a way of seeing things that can only be solved numerically, giving a useful tool to gain insights that complement the numeric simulations usually inevitable here, and shows an intriguing connection to discrete Fourier transform and spectral properties of standard graphs.
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Affiliation(s)
- Dmitri V. Stass
- Voevodsky Institute of Chemical Kinetics and Combustion, 630090 Novosibirsk, Russia;
- International Tomography Center, 630090 Novosibirsk, Russia
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3
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Konowalczyk M, Foster Vander Elst O, Storey JG. Development of lock-in based overtone modulated MARY spectroscopy for detection of weak magnetic field effects. Phys Chem Chem Phys 2021; 23:1273-1284. [PMID: 33355552 DOI: 10.1039/d0cp04814c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Modulated magnetically altered reaction yield (ModMARY) spectroscopy is a derivative variant of fluorescence detected magnetic field effect measurement, where the applied magnetic field has both a constant and a modulated component. As in many derivative spectroscopy techniques, the signal to noise ratio scales with the magnitude of the modulation. High modulation amplitudes, however, distort the signal and can obscure small features of the measured spectrum. In order to detect weak magnetic field effects (including the low field effect) a balance of the two has to be found. In this work we look in depth at the origin of the distortion of the MARY signal by field modulation. We then present an overtone detection scheme, as well as a data analysis method which allows for correct fitting of both harmonic and overtone signals of the modulation broadened MARY data. This allows us to robustly reconstruct the underlying MARY curve at different modulation depths. To illustrate the usefulness of the technique, we show measurements and analysis of a well known magnetosensitive system of pyrene/1,3-dicyanobenzene (Py/DCB). The measurements of first (h1) and second (h2) harmonic spectra are performed at different modulation depths for both natural isotopic abundance (PyH10), and perdeuterated (PyD10) pyrene samples.
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Affiliation(s)
- Marcin Konowalczyk
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, Oxford OX1 3QZ, UK. and Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford OX1 3QR, UK
| | | | - Jonathan G Storey
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford OX1 3QR, UK
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4
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Kim D, Lee YJ, Ahn DH, Song JW, Seo J, Lee H. Peptoid-Conjugated Magnetic Field-Sensitive Exciplex System at High and Low Solvent Polarities. J Phys Chem Lett 2020; 11:4668-4677. [PMID: 32441939 DOI: 10.1021/acs.jpclett.0c00636] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The magnetic field effect (MFE) in exciplex emission (ExE) has been studied for decades, but it has been observed to occur only in solvents with a limited range of polarity. This limitation is mainly due to the reversible interconversion collapse between two quenching products of the photoinduced electron transfer, the exciplex and magnetic field-sensitive radical ion pair (RIP) beyond that polarity range. In a nonpolar solvent, the formation of RIPs is suppressed, whereas in a polar solvent, the probability of their re-encounter forming the exciplexes decreases. In this study, we developed new exciplex-forming (phenyl-phenanthrene)-(phenyl-N,N-dimethylaniline)-peptoid conjugates (PhD-PCs) to overcome this limitation. The well-defined peptoid structure allows precise control of the distance and the relative orientation between two conjugated moieties. Steady-state and time-resolved spectroscopic data indicate that the PhD-PCs can maintain the reversibility, which allows MFEs in ExE regardless of the solvent polarity. Subtle differences between the ExEs of the PhD-PCs were observed and explained by their exciplex geometries obtained through time-dependent density functional theory (TD-DFT) calculations.
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Affiliation(s)
- Dongkyum Kim
- Department of Chemistry, Gwangju Institute of Science and Technology (GIST), 123 Cheomdan Gwagiro, Buk-gu, Gwangju 61005, Republic of Korea
| | - Yen Jea Lee
- Department of Chemistry, Gwangju Institute of Science and Technology (GIST), 123 Cheomdan Gwagiro, Buk-gu, Gwangju 61005, Republic of Korea
| | - Dae-Hwan Ahn
- Department of Chemistry Education, Daegu University, Gyeongsan-si 113-8656, Republic of Korea
| | - Jong-Won Song
- Department of Chemistry Education, Daegu University, Gyeongsan-si 113-8656, Republic of Korea
| | - Jiwon Seo
- Department of Chemistry, Gwangju Institute of Science and Technology (GIST), 123 Cheomdan Gwagiro, Buk-gu, Gwangju 61005, Republic of Korea
| | - Hohjai Lee
- Department of Chemistry, Gwangju Institute of Science and Technology (GIST), 123 Cheomdan Gwagiro, Buk-gu, Gwangju 61005, Republic of Korea
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5
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Stass DV. On algebraic properties of the sub-block of zero field hyperfine Hamiltonian with penultimate total spin projection for arbitrary hyperfine structure, and field dependence of radical pair recombination probability in the vicinity of zero field. J Chem Phys 2019; 151:184112. [DOI: 10.1063/1.5127217] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Dmitri V. Stass
- Voevodsky Institute of Chemical Kinetics and Combustion, 630090 Novosibirsk, Russia and Novosibirsk State University, 630090 Novosibirsk, Russia
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6
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Sannikova VA, Davydova MP, Sherin PS, Babenko SV, Korolev VV, Stepanov AA, Nikul'shin PV, Kalneus EV, Vasilevsky SF, Benassi E, Melnikov AR. Determination of Hyperfine Coupling Constants of Fluorinated Diphenylacetylene Radical Anions by Magnetic Field-Affected Reaction Yield Spectroscopy. J Phys Chem A 2019; 123:505-516. [PMID: 30566354 DOI: 10.1021/acs.jpca.8b10306] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Magnetic field-affected reaction yield (MARY) spectroscopy is a spin chemistry technique for detecting short-lived radical ions. Having sensitivity to transient species with lifetimes as short as nanoseconds, MARY spectroscopy usually does not provide detailed information on their magnetic resonance parameters, except for simple systems with equivalent magnetic nuclei. In this work, the radical anions of two fluorinated diphenylacetylene derivatives with nonequivalent magnetic nuclei and unknown hyperfine coupling constants ( AHF) were investigated by MARY spectroscopy. The MARY spectra were found to be resolved and have resonance lines in nonzero magnetic fields, which are determined by the AHF values. Simple relationships between the positions of resonance MARY lines and the AHF values were established from the analysis of the different Hamiltonian block contributions to the MARY spectrum. The obtained experimental AHF values are in agreement with the results of quantum chemical calculations at the density functional theory level.
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Affiliation(s)
- Victoria A Sannikova
- Institute of Chemical Kinetics and Combustion SB RAS , 3, Institutskaya Str. , 630090 Novosibirsk , Russian Federation.,Novosibirsk State University , 2, Pirogova Str. , 630090 Novosibirsk , Russian Federation
| | - Maria P Davydova
- Institute of Chemical Kinetics and Combustion SB RAS , 3, Institutskaya Str. , 630090 Novosibirsk , Russian Federation.,A.V. Nikolaev Institute of Inorganic Chemistry SB RAS , 3, Akademika Lavrentieva Ave. , 630090 Novosibirsk , Russian Federation
| | - Peter S Sherin
- Novosibirsk State University , 2, Pirogova Str. , 630090 Novosibirsk , Russian Federation.,International Tomography Center , 3a, Institutskaya Str. , 630090 Novosibirsk , Russian Federation
| | - Simon V Babenko
- Institute of Chemical Kinetics and Combustion SB RAS , 3, Institutskaya Str. , 630090 Novosibirsk , Russian Federation
| | - Valeri V Korolev
- Institute of Chemical Kinetics and Combustion SB RAS , 3, Institutskaya Str. , 630090 Novosibirsk , Russian Federation
| | - Alexander A Stepanov
- Institute of Chemical Kinetics and Combustion SB RAS , 3, Institutskaya Str. , 630090 Novosibirsk , Russian Federation.,Novosibirsk State University , 2, Pirogova Str. , 630090 Novosibirsk , Russian Federation
| | - Pavel V Nikul'shin
- N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry SB RAS , 9, Akademika Lavrentieva Ave. , 630090 Novosibirsk , Russian Federation
| | - Evgeny V Kalneus
- Institute of Chemical Kinetics and Combustion SB RAS , 3, Institutskaya Str. , 630090 Novosibirsk , Russian Federation
| | - Sergei F Vasilevsky
- Institute of Chemical Kinetics and Combustion SB RAS , 3, Institutskaya Str. , 630090 Novosibirsk , Russian Federation.,Novosibirsk State University , 2, Pirogova Str. , 630090 Novosibirsk , Russian Federation
| | - Enrico Benassi
- Novosibirsk State University , 2, Pirogova Str. , 630090 Novosibirsk , Russian Federation.,Department of Chemistry , Hexi University , 734000 Zhangye , China
| | - Anatoly R Melnikov
- Institute of Chemical Kinetics and Combustion SB RAS , 3, Institutskaya Str. , 630090 Novosibirsk , Russian Federation.,Novosibirsk State University , 2, Pirogova Str. , 630090 Novosibirsk , Russian Federation
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7
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Hoang HM, Pham VTB, Grampp G, Kattnig DR. Magnetic Field-Sensitive Radical Pair Dynamics in Polymethylene Ether-Bridged Donor-Acceptor Systems. ACS OMEGA 2018; 3:10296-10305. [PMID: 30198006 PMCID: PMC6120740 DOI: 10.1021/acsomega.8b01232] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Accepted: 08/20/2018] [Indexed: 05/13/2023]
Abstract
Donor-acceptor systems forming exciplexes are versatile models for the study of magnetic field effects (MFEs) on charge recombination reactions. The MFEs originate from singlet-triplet interconversion within transient radical ion pairs (RIPs), which exist in a dynamic equilibrium with the exciplexes. Here, we describe the synthesis and MFEs of the chain-linked N,N-dimethylaniline (DMA)/9-methylanthracene (MAnt) donor-acceptor system MAnt-(CH2) n -O-CH2-CH2-DMA for n = 6, 8, 10, and 16. The MFEs are found to increase with increasing chain length. Effects as large as 37.5% have been observed for the long-chain compound with n = 16. The solvent dependence of the MFEs at magnetic field intensity 75 mT is reported. For the range of solvent static dielectric constants εs = 6.0-36.0, the MFEs go through a maximum for intermediate polarities, for which the direct formation of RIPs prevails and their dissociation and reencounter are balanced. Field-resolved measurements (MARY spectra) are reported for solutions in butyronitrile. The MARY spectra reveal that for n = 8, 10, 16, the average exchange interaction is negligible during the coherent lifetime of the radical pair. However, singlet-triplet dephasing broadens the lineshape; the shorter the linker, the more pronounced this effect is. For n = 6, a dip in the fluorescence intensity reveals a nonzero average exchange coupling of the order of ±5 mT. We discuss the field-dependence in the framework of the semiclassical theory taking spin-selective recombination, singlet-triplet dephasing, and exchange coupling into account. Singlet recombination rates of the order of 0.1 ns-1 and various degrees of singlet-triplet dephasing govern the spin dynamics. In addition, because of a small free energy gap between the exciplex and the locally excited fluorophore quencher pair, a fully reversible interconversion between the RIP, exciplex, and locally excited fluorophore is revealed by spectrally resolved MFE measurements for the long-chain systems (n = 10, 16).
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Affiliation(s)
- Hao Minh Hoang
- Ho
Chi Minh City University of Technology and Education, Vo Van Ngan 01, Linh Chieu Ward, Thu Duc District, Ho Chi Minh City 700000, Vietnam
- Institute
of Physical and Theoretical Chemistry, Graz
University of Technology, Stremayrgasse 9/I, A-8010 Graz, Austria
| | - Van Thi Bich Pham
- Institute
of Physical and Theoretical Chemistry, Graz
University of Technology, Stremayrgasse 9/I, A-8010 Graz, Austria
| | - Günter Grampp
- Institute
of Physical and Theoretical Chemistry, Graz
University of Technology, Stremayrgasse 9/I, A-8010 Graz, Austria
| | - Daniel R. Kattnig
- Living
Systems Institute and Department of Physics, University of Exeter, Stocker Road, Exeter, Devon EX4 4QD, United Kingdom
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8
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Ivanov KL, Wagenpfahl A, Deibel C, Matysik J. Spin-chemistry concepts for spintronics scientists. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2017; 8:1427-1445. [PMID: 28900597 PMCID: PMC5530719 DOI: 10.3762/bjnano.8.143] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 06/13/2017] [Indexed: 05/03/2023]
Abstract
Spin chemistry and spintronics developed independently and with different terminology. Until now, the interaction between the two fields has been very limited. In this review, we compile the two "languages" in an effort to enhance communication. We expect that knowledge of spin chemistry will accelerate progress in spintronics.
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Affiliation(s)
- Konstantin L Ivanov
- International Tomography Center, Siberian Branch of Russian Academy of Science, Institutskaya 3а, Novosibirsk, 630090 Russia
- Novosibirsk State University, Institutskaya 3а, Novosibirsk, 630090 Russia
| | | | - Carsten Deibel
- Institut für Physik, Technische Universität Chemnitz, 09126 Chemnitz, Germany
| | - Jörg Matysik
- Universität Leipzig, Institut für Analytische Chemie, Linnéstr. 3, D-04103 Leipzig, Germany
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9
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Pham VTB, Hoang HM, Grampp G, Kattnig DR. Effects of Preferential Solvation Revealed by Time-Resolved Magnetic Field Effects. J Phys Chem B 2017; 121:2677-2683. [PMID: 28263599 PMCID: PMC5377269 DOI: 10.1021/acs.jpcb.7b00510] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
External
magnetic fields can impact recombination yields of photoinduced electron
transfer reactions by affecting the spin dynamics in transient, spin-correlated
radical pair intermediates. For exciplex-forming donor–acceptor
systems, this magnetic field effect (MFE) can be investigated sensitively
by studying the delayed recombination fluorescence. Here, we investigate
the effect of preferential solvation in microheterogeneous solvent
mixtures on the radical pair dynamics of the system 9,10-dimethylanthracene
(fluorophore)/N,N-dimethylaniline
(quencher) by means of time-resolved magnetic field effect (TR-MFE)
measurements, wherein the exciplex emission is recorded in the absence
and the presence of an external magnetic field using time-correlated
single photon counting (TCSPC). In microheterogeneous environments,
the MFE of the exciplex emission occurs on a faster time scale than
in iso-dielectric homogeneous solvents. In addition, the local polarity
reported by the exciplex is enhanced compared to homogeneous solvent
mixtures of the same macroscopic permittivity. Detailed analyses of
the TR-MFE reveal that the quenching reaction directly yielding the
radical ion pair is favored in microheterogeneous environments. This
is in stark contrast to homogeneous media, for which the MFE predominantly
involves direct formation of the exciplex, its subsequent dissociation
to the magneto-sensitive radical pair, and re-encounters. These observations
provide evidence for polar microdomains and enhanced caging, which
are shown to have a significant impact on the reaction dynamics in
microheterogeneous binary solvents.
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Affiliation(s)
- Van Thi Bich Pham
- Institute of Physical and Theoretical Chemistry, Graz University of Technology , Stremayrgasse 9/I, A-8010 Graz, Austria
| | - Hao Minh Hoang
- Institute of Physical and Theoretical Chemistry, Graz University of Technology , Stremayrgasse 9/I, A-8010 Graz, Austria.,Ho Chi Minh City University of Technology and Education , Vo Van Ngan 01, Linh Chieu Ward, Thu Duc District, Ho Chi Minh City, Vietnam
| | - Günter Grampp
- Institute of Physical and Theoretical Chemistry, Graz University of Technology , Stremayrgasse 9/I, A-8010 Graz, Austria
| | - Daniel R Kattnig
- Physical and Theoretical Chemistry Laboratory, University of Oxford , South Parks Road, Oxford OX1 3QZ, U.K
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10
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Melnikov AR, Verkhovlyuk VN, Kalneus EV, Korolev VV, Borovkov VI, Sherin PS, Davydova MP, Vasilevsky SF, Stass DV. Estimation of the Fraction of Spin-Correlated Radical Ion Pairs in Irradiated Alkanes using Magnetosensitive Recombination Luminescence from Exciplexes Generated upon Recombination of a Probe Pair. ACTA ACUST UNITED AC 2016. [DOI: 10.1515/zpch-2016-0819] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
We suggest a convenient probe exciplex system for studies in radiation spin chemistry based on a novel acceptor-substituted diphenylacetylene, 1-(phenylethynyl)-4-(trifluoromethyl)benzene that has a very short fluorescence lifetime (<200 ps) and low quantum yield (0.01) of intrinsic emission, provides efficient electron capture in alkanes and efficient exciplex formation upon recombination in pair with DMA radical cation, while exhibiting a shifted to red exciplex emission band as compared to the parent system DMA – diphenylacetylene. After chemical, luminescent, radiation and spin-chemical characterization of the new system we used the magnitude of magnetic field effect in its exciplex emission band for experimental estimation of the fraction of spin-correlated radical ion pairs under X-irradiation with upper energy cutoff 40 keV in a set of 11 alkanes. For linear and branched alkanes magnetic field effects and the corresponding fractions are approximately 19–20% and 0.28, while for cyclic alkanes they are lower at 16–17% and 0.22, respectively.
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Affiliation(s)
- Anatoly R. Melnikov
- Voevodsky Institute of Chemical Kinetics and Combustion SB RAS, 3, Institutskaya Str., 630090 Novosibirsk, Russian Federation
- Novosibirsk State University, 2, Pirogova Str., 630090 Novosibirsk, Russian Federation
| | - Vladimir N. Verkhovlyuk
- Voevodsky Institute of Chemical Kinetics and Combustion SB RAS, 3, Institutskaya Str., 630090 Novosibirsk, Russian Federation
| | - Evgeny V. Kalneus
- Voevodsky Institute of Chemical Kinetics and Combustion SB RAS, 3, Institutskaya Str., 630090 Novosibirsk, Russian Federation
| | - Valeri V. Korolev
- Voevodsky Institute of Chemical Kinetics and Combustion SB RAS, 3, Institutskaya Str., 630090 Novosibirsk, Russian Federation
| | - Vsevolod I. Borovkov
- Novosibirsk State University, 2, Pirogova Str., 630090 Novosibirsk, Russian Federation
- Voevodsky Institute of Chemical Kinetics and Combustion SB RAS, 3, Institutskaya Str., 630090, Russian Federation
| | - Peter S. Sherin
- Novosibirsk State University, 2, Pirogova Str., 630090 Novosibirsk, Russian Federation
- International Tomography Center SB RAS, 3a, Institutskaya Str., 630090 Novosibirsk, Russian Federation
| | - Maria P. Davydova
- Novosibirsk State University, 2, Pirogova Str., 630090 Novosibirsk, Russian Federation
- Voevodsky Institute of Chemical Kinetics and Combustion SB RAS, 3, Institutskaya Str., 630090, Russian Federation
| | - Sergei F. Vasilevsky
- Novosibirsk State University, 2, Pirogova Str., 630090 Novosibirsk, Russian Federation
- Voevodsky Institute of Chemical Kinetics and Combustion SB RAS, 3, Institutskaya Str., 630090, Russian Federation
| | - Dmitri V. Stass
- Novosibirsk State University, 2, Pirogova Str., 630090 Novosibirsk, Russian Federation
- Voevodsky Institute of Chemical Kinetics and Combustion SB RAS, 3, Institutskaya Str., 630090, Russian Federation
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11
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Sosnovsky DV, Jeschke G, Matysik J, Vieth HM, Ivanov KL. Level crossing analysis of chemically induced dynamic nuclear polarization: Towards a common description of liquid-state and solid-state cases. J Chem Phys 2016; 144:144202. [DOI: 10.1063/1.4945341] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Denis V. Sosnovsky
- International Tomography Centre of SB RAS, Institutskaya 3a, 630090, Novosibirsk, Russia
- Novosibirsk State University, Pirogova 2, 630090, Novosibirsk, Russia
| | - Gunnar Jeschke
- Institut für Physikalische Chemie, ETH Zürich, Vladimir-Prelog-Weg 2, CH-8093 Zürich, Switzerland
| | - Jörg Matysik
- Institut für Analytische Chemie, Universität Leipzig, Linnéstr. 3, D-04103 Leipzig, Germany
| | - Hans-Martin Vieth
- International Tomography Centre of SB RAS, Institutskaya 3a, 630090, Novosibirsk, Russia
- Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
| | - Konstantin L. Ivanov
- International Tomography Centre of SB RAS, Institutskaya 3a, 630090, Novosibirsk, Russia
- Novosibirsk State University, Pirogova 2, 630090, Novosibirsk, Russia
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12
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Klein JH, Schmidt D, Steiner UE, Lambert C. Complete Monitoring of Coherent and Incoherent Spin Flip Domains in the Recombination of Charge-Separated States of Donor-Iridium Complex-Acceptor Triads. J Am Chem Soc 2015; 137:11011-21. [DOI: 10.1021/jacs.5b04868] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Johannes H. Klein
- Wilhelm
Conrad Röntgen Research Center for Complex Material Systems,
Würzburg, Center for Nanosystems Chemistry, Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - David Schmidt
- Wilhelm
Conrad Röntgen Research Center for Complex Material Systems,
Würzburg, Center for Nanosystems Chemistry, Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | | | - Christoph Lambert
- Wilhelm
Conrad Röntgen Research Center for Complex Material Systems,
Würzburg, Center for Nanosystems Chemistry, Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
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13
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Fedorenko SG, Burshtein AI. Kinetics of exciplex formation/dissipation in reaction following Weller Scheme II. J Chem Phys 2014; 141:114504. [DOI: 10.1063/1.4895625] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Affiliation(s)
- S. G. Fedorenko
- Voevodsky Institute of Chemical Kinetics and Combustion, Novosibirsk, Russia
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14
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Hoang HM, Pham TB, Grampp G, Kattnig DR. Exciplexes versus Loose Ion Pairs: How Does the Driving Force Impact the Initial Product Ratio of Photoinduced Charge Separation Reactions? J Phys Chem Lett 2014; 5:3188-3194. [PMID: 25243054 PMCID: PMC4166680 DOI: 10.1021/jz501575r] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2014] [Accepted: 08/29/2014] [Indexed: 05/24/2023]
Abstract
Many donor-acceptor systems can undergo a photoinduced charge separation reaction, yielding loose ion pairs (LIPs). LIPs can be formed either directly via (distant) electron transfer (ET) or indirectly via the dissociation of an initially formed exciplex or tight ion pair. Establishing the prevalence of one of the reaction pathways is challenging because differentiating initially formed exciplexes from LIPs is difficult due to similar spectroscopic footprints. Hence, no comprehensive reaction model has been established for moderately polar solvents. Here, we employ an approach based on the time-resolved magnetic field effect (MFE) of the delayed exciplex luminescence to distinguish the two reaction channels. We focus on the effects of the driving force of ET and the solvent permittivity. We show that, surprisingly, the exciplex channel is significant even for an exergonic ET system with a free energy of ET of -0.58 eV and for the most polar solutions studied (butyronitrile). Our findings demonstrate that exciplexes play a crucial role even in polar solvents and at moderate driving forces, contrary to what is usually assumed.
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Affiliation(s)
- Hao Minh Hoang
- Institute of Physical
and Theoretical Chemistry, Graz University of Technology, Streymayrgasse 9/I, A-8010 Graz, Austria
| | - Thi Bich
Van Pham
- Institute of Physical
and Theoretical Chemistry, Graz University of Technology, Streymayrgasse 9/I, A-8010 Graz, Austria
| | - Günter Grampp
- Institute of Physical
and Theoretical Chemistry, Graz University of Technology, Streymayrgasse 9/I, A-8010 Graz, Austria
| | - Daniel R. Kattnig
- Physical
and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom
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15
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Verkhovlyuk V, Anishchik S, Molin Y, Anisimov O. Inhomogeneous contribution to the width of zero-field MARY line. Mol Phys 2014. [DOI: 10.1080/00268976.2014.948515] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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16
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Burshtein AI, Ivanov AI. Diffusion affected magnetic field effect in exciplex fluorescence. J Chem Phys 2014; 141:024508. [DOI: 10.1063/1.4886809] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
| | - Anatoly I. Ivanov
- Volgograd State University, University Avenue, 100, Volgograd 400062, Russia
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17
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Richert S, Rosspeintner A, Landgraf S, Grampp G, Vauthey E, Kattnig DR. Time-resolved magnetic field effects distinguish loose ion pairs from exciplexes. J Am Chem Soc 2013; 135:15144-52. [PMID: 24041160 PMCID: PMC3797520 DOI: 10.1021/ja407052t] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
We describe the experimental investigation
of time-resolved magnetic
field effects in exciplex-forming organic donor–acceptor systems.
In these systems, the photoexcited acceptor state is predominantly
deactivated by bimolecular electron transfer reactions (yielding radical
ion pairs) or by direct exciplex formation. The delayed fluorescence
emitted by the exciplex is magnetosensitive if the reaction pathway
involves loose radical ion pair states. This magnetic field effect
results from the coherent interconversion between the electronic singlet
and triplet radical ion pair states as described by the radical pair
mechanism. By monitoring the changes in the exciplex luminescence
intensity when applying external magnetic fields, details of the reaction
mechanism can be elucidated. In this work we present results obtained
with the fluorophore-quencher pair 9,10-dimethylanthracene/N,N-dimethylaniline (DMA) in solvents of
systematically varied permittivity. A simple theoretical model is
introduced that allows discriminating the initial state of quenching,
viz., the loose ion pair and the exciplex, based on the time-resolved
magnetic field effect. The approach is validated by applying it to
the isotopologous fluorophore-quencher pairs pyrene/DMA and pyrene-d10/DMA. We detect that both the exciplex and
the radical ion pair are formed during the initial quenching stage.
Upon increasing the solvent polarity, the relative importance of the
distant electron transfer quenching increases. However, even in comparably
polar media, the exciplex pathway remains remarkably significant.
We discuss our results in relation to recent findings on the involvement
of exciplexes in photoinduced electron transfer reactions.
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Affiliation(s)
- Sabine Richert
- Department of Physical Chemistry, University of Geneva , 30 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland
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18
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Wedge CJ, Lau JCS, Ferguson KA, Norman SA, Hore PJ, Timmel CR. Spin-locking in low-frequency reaction yield detected magnetic resonance. Phys Chem Chem Phys 2013; 15:16043-53. [PMID: 23963374 DOI: 10.1039/c3cp52019f] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The purported effects of weak magnetic fields on various biological systems from animal magnetoreception to human health have generated widespread interest and sparked much controversy in the past decade. To date the only well established mechanism by which the rates and yields of chemical reactions are known to be influenced by magnetic fields is the radical pair mechanism, based on the spin-dependent reactivity of radical pairs. A diagnostic test for the operation of the radical pair mechanism was proposed by Henbest et al. [J. Am. Chem. Soc., 2004, 126, 8102] based on the combined effects of weak static magnetic fields and radiofrequency oscillating fields in a reaction yield detected magnetic resonance experiment. Here we investigate the effects on radical pair reactions of applying relatively strong oscillating fields, both parallel and perpendicular to the static field. We demonstrate the importance of understanding the effect of the strength of the radiofrequency oscillating field; our experiments demonstrate that there is an optimal oscillating field strength above which the observed signal decreases in intensity and eventually inverts. We establish the correlation between the onset of this effect and the hyperfine structure of the radicals involved, and identify the existence of 'overtone' type features appearing at multiples of the expected resonance field position.
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Affiliation(s)
- C J Wedge
- Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, South Parks Road, Oxford, OX1 3QR, UK.
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19
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Pal K, Grampp G, Kattnig DR. Solvation dynamics of a radical ion pair in micro-heterogeneous binary solvents: a semi-quantitative study utilizing MARY line-broadening experiments. Chemphyschem 2013; 14:3389-99. [PMID: 23939826 DOI: 10.1002/cphc.201300435] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Revised: 07/15/2013] [Indexed: 11/10/2022]
Abstract
This work aims at elucidating the mechanism of solvation of a radical ion pair (RIP) in a micro-heterogeneous binary solvent mixture using magnetically affected reaction yield (MARY) spectroscopy. For the exciplex-forming 9,10-dimethylanthracene/N,N-dimethylaniline system a comparative, composition-dependent MARY line-broadening study is undertaken in a heterogeneous (toluene/dimethylsulfoxide) and a quasi-homogenous (propyl acetate/butyronitrile) solvent mixture. The half-saturation field extrapolated to zero-quencher concentration, B(1/2), and the self-exchange rate constants are analyzed in the light of solvent dynamical properties of the mixtures and a dielectric continuum solvation model. The dependence of B(1/2) on the solvent composition is explained by cluster formation giving rise to shortened RIP lifetimes. The results are in qualitative agreement with the continuum solvation model suggesting that it could serve as a theoretical basis for quantitative modeling.
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Affiliation(s)
- Kunal Pal
- Institute of Physical and Theoretical Chemistry, Graz University of Technolgy, Stremayrgasse 9/Z2, A-8010 Graz (Austria).
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20
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Selective quenching of magnetic field effect for radical ion pairs with widely different hyperfine couplings. Chem Phys Lett 2013. [DOI: 10.1016/j.cplett.2013.05.043] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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21
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Dodin DV, Ivanov AI, Burshtein AI. Hyperfine interaction mechanism of magnetic field effects in sequential fluorophore and exciplex fluorescence. J Chem Phys 2013; 138:124102. [DOI: 10.1063/1.4795576] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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22
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Roy P, Jana AK, M.B G, Nath DN. Studies on B1/2 value of pyrene–dimethylaniline radical pair system in single and binary solvents. Chem Phys Lett 2012. [DOI: 10.1016/j.cplett.2012.10.029] [Citation(s) in RCA: 2] [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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23
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Sergey N, Verkhovlyuk V, Kalneus E, Korolev V, Melnikov A, Burdukov A, Stass D, Molin YN. Registration of radical anions of Al, Ga, In tris-8-oxyquinolinates by magnetosensitive and spectrally resolved recombination luminescence in benzene solutions. Chem Phys Lett 2012. [DOI: 10.1016/j.cplett.2012.08.069] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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24
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Dodin DV, Ivanov AI, Burshtein AI. Magnetic field effect in fluorescence of excited fluorophore equilibrated with exciplex that reversibly dissociates into radical-ion pair undergoing the spin conversion. J Chem Phys 2012; 137:024511. [DOI: 10.1063/1.4734306] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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25
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Pal K, Kattnig DR, Grampp G, Landgraf S. Experimental observation of preferential solvation on a radical ion pair using MARY spectroscopy. Phys Chem Chem Phys 2012; 14:3155-61. [PMID: 22286393 DOI: 10.1039/c2cp23858f] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The effect of preferential solvation on the exciplex luminescence detected magnetic field effect has been studied using magnetic-field-effect-on-reaction-yield (MARY) spectroscopy. By designing solvent mixtures which can provide a micro-environment around the magneto-sensitive radical ion pair (RIP) from highly heterogeneous to quasi-homogenous, the effect of the polarity scan on an absolute magnetic field effect (χ(E)) and B(1/2) (the field value marking half saturation) has been studied on the system 9,10-dimethylanthracene (fluorophore)/N,N'-dimethylaniline (quencher). While the trend in χ(E) (although with subtle differences) follows the usual norm of passing through maxima with increasing polarity, the B(1/2) values show either a large monotonic decrease (for heterogeneous solvents) or remain constant (for quasi-homogenous systems) with increasing polarity. The observations have been interpreted invoking the concept of amplification of the "cage-effect" as a result of preferential solvation in binary solvents and its influence on the decaying exciplex. The use of ternary solvents further confirms the proposed mechanism. Additionally electron hopping from the radical ion pair to the surrounding neutral donor molecules could also possibly contribute to the observed trend.
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Affiliation(s)
- Kunal Pal
- Institute of Physical and Theoretical Chemistry, Graz University of Technology, Stremayrgasse 9/I, A-8010 Graz, Austria
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26
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Maeda K, Neil SRT, Henbest KB, Weber S, Schleicher E, Hore PJ, Mackenzie SR, Timmel CR. Following Radical Pair Reactions in Solution: A Step Change in Sensitivity Using Cavity Ring-Down Detection. J Am Chem Soc 2011; 133:17807-15. [DOI: 10.1021/ja206783t] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Kiminori Maeda
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford, OX1 3QR, U.K
- Centre for Advanced Electron Spin Resonance, University of Oxford, OX1 3QR, U.K
| | - Simon R. T. Neil
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, Oxford, OX1 3QZ, U.K
| | - Kevin B. Henbest
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford, OX1 3QR, U.K
- Centre for Advanced Electron Spin Resonance, University of Oxford, OX1 3QR, U.K
| | - Stefan Weber
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstraße 21, 79104 Freiburg, Germany
| | - Erik Schleicher
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstraße 21, 79104 Freiburg, Germany
| | - P. J. Hore
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, Oxford, OX1 3QZ, U.K
| | - Stuart R. Mackenzie
- Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, Oxford, OX1 3QZ, U.K
| | - Christiane R. Timmel
- Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, Oxford, OX1 3QR, U.K
- Centre for Advanced Electron Spin Resonance, University of Oxford, OX1 3QR, U.K
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27
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Sergey N, Burdukov A, Pervukhina N, Kuibida L, Pozdnyakov I, Stass D. MARY spectroscopy in the presence of coordination compound Zn(hfac)2(PPO)2. Chem Phys Lett 2011. [DOI: 10.1016/j.cplett.2011.01.056] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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28
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Kattnig DR, Rosspeintner A, Grampp G. Magnetic field effects on exciplex-forming systems: the effect on the locally excited fluorophore and its dependence on free energy. Phys Chem Chem Phys 2010; 13:3446-60. [PMID: 21180733 DOI: 10.1039/c0cp01517b] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
This study addresses magnetic field effects in exciplex forming donor-acceptor systems. For moderately exergonic systems, the exciplex and the locally excited fluorophore emission are found to be magneto-sensitive. A previously introduced model attributing this finding to excited state reversibility is confirmed. Systems characterised by a free energy of charge separation up to approximately -0.35 eV are found to exhibit a magnetic field effect on the fluorophore. A simple three-state model of the exciplex is introduced, which uses the reaction distance and the asymmetric electron transfer reaction coordinate as pertinent variables. Comparing the experimental emission band shapes with those predicted by the model, a semi-quantitative picture of the formation of the magnetic field effect is developed based on energy hypersurfaces. The model can also be applied to estimate the indirect contribution of the exchange interaction, even if the perturbative approach fails. The energetic parameters that are essential for the formation of large magnetic field effects on the exciplex are discussed.
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29
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Mladenova B, Kattnig DR, Grampp G. ESR-Investigations on the Dynamic Solvent Effects of Degenerate Electron Exchange Reactions. Part I: Cyanobenzenes. Z PHYS CHEM 2009. [DOI: 10.1524/zpch.2006.220.4.543] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Summary
The rates of degenerate electron exchange (electron self-exchange) of various cyanobenzenes have been measured by EPR line broadening technique in nine different solvents at room temperature. The molecules studied comprise besides benzene-1,2-dicarbonitrile, benzene-1,4-dicarbonitrile and benzene-1,2,4,5-tetracarbonitrile, the two isomeric tricyanobenzenes, benzene-1,2,3-tricarbonitrile and benzene-1,2,4-tricarbonitrile, the anion radicals of which have not been characterized before.
The experimentally observed rates vary from 4.5 × 108 to 44.0 × 108 M−1 s−1 and show the pronounced dependence on the longitudinal relaxation times, τL, of the solvents. The solvent dynamical effect so manifested is confirmed with remarkable clarity using solvents spanning a wide range of τL-values, which comprise acetonitrile (0.2 ps) and o-dichlorobenzene (6.0 ps) at its extremes. The rate constants are compared with Marcus theory using the continuum model (CM) and the mean spherical approximation (MSA) for the outer sphere reorganization energies and Nelson’s method for the inner sphere reorganization energies. Furthermore, an estimation of the resonance splitting energies, V
RP, is given based on the experimental rates.
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30
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Awasthi K, Iimori T, Ohta N. Synergy Effects of Electric and Magnetic Fields on Locally Excited-State Fluorescence of Photoinduced Electron Transfer Systems in a Polymer Film. J Phys Chem A 2009; 113:10603-9. [DOI: 10.1021/jp905579p] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Kamlesh Awasthi
- Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan
| | - Toshifumi Iimori
- Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan
| | - Nobuhiro Ohta
- Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0020, Japan
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31
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Kattnig DR, Rosspeintner A, Grampp G. Fully reversible interconversion between locally excited fluorophore, exciplex, and radical ion pair demonstrated by a new magnetic field effect. Angew Chem Int Ed Engl 2008; 47:960-2. [PMID: 18092310 DOI: 10.1002/anie.200703488] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Daniel R Kattnig
- Institute of Physical and Theoretical Chemistry, Graz University of Technology, Technikerstrasse 4, 8010 Graz, Austria
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32
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Kattnig D, Rosspeintner A, Grampp G. Reversibler Austausch zwischen lokal angeregtem Fluorophor, Exciplex und Radikalionenpaar – ein neuer Magnetfeldeffekt. Angew Chem Int Ed Engl 2008. [DOI: 10.1002/ange.200703488] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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33
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Matveeva AG, Sviridenko FB, Korolev VV, Kuibida LV, Stass DV, Shundrin LA, Reznikov VA, Grampp GG. Difficulties in building radiation-generated three-spin systems using spin-labeled luminophores. J Phys Chem A 2008; 112:183-93. [PMID: 18088106 DOI: 10.1021/jp076835e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Aromatic compounds are well-known acceptors of primary radical ions that are formed under high-energy irradiation of nonpolar systems. Thus formed radical ion pairs recombine and produce magnetosensitive fluorescence, which helps study the short-lived radical ions. It was initially suggested that a simple introduction of a spin label into the original arene would allow an easy transition from two-spin to three-spin systems, retaining the experimental techniques available for radical pairs. However, it turned out that spin-labeled arenes often do not produce magnetosensitive fluorescence in the conditions of a conventional radiochemical experiment. To understand the effect of the introduced spin label, we synthesized a series of compounds with the general structure "stable 3-imidazoline radical-two-carbon bridge-naphthalene" as well as their diamagnetic analogues. By use of this set of acceptors, we determined the processes that ruin the observed signal and established their connection with the chemical structure of the compound. We found that the compounds with flexible (saturated) two-carbon bridges between the luminophore and the stable radical moieties exist in solution in folded conformation, which leads to suppression of luminescence from naphthalene due to efficient through-space exchange quenching of the excited state by the radical. Increasing the rigidity of the bridge by introducing the double bond drastically increases the reactivity of the extended pi-system. In these compounds, the energy released upon recombination is spent in radiationless processes of chemical transformations both at the stage of the radical ion and at the stage of the electronically excited molecule.
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Affiliation(s)
- Anna G Matveeva
- Institute of Chemical Kinetics and Combustion SB RAS, ul. Institutskaya, 3, 630090 Novosibirsk, Russia
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34
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Miura T, Maeda K, Arai T. The spin mixing process of a radical pair in low magnetic field observed by transient absorption detected nanosecond pulsed magnetic field effect. J Phys Chem A 2007; 110:4151-6. [PMID: 16553365 DOI: 10.1021/jp056488d] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The spin mixing process of the radical pair in the sodium dodecyl sulfate (SDS) micelle is studied by using a novel technique nanosecond pulsed magnetic field effect on transient absorption. We have developed the equipment for a nanosecond pulsed magnetic field and observed its effect on the radical pair reaction. A decrease of the free radical yield by a reversely directed pulsed magnetic field that cancels static field is observed, and the dependence on its magnitude, which is called pulsed MARY (magnetic field effect on reaction yield) spectra, is studied. The observed spectra reflect the spin mixing in 50-200 ns and show clear time evolution. Theoretical simulation of pulsed MARY spectra based on a single site modified Liouville equation indicates that the fast spin dephasing processes induced by the modulation of electron-electron spin interaction by molecular reencounter affect to the coherent spin mixing by a hyperfine interaction in a low magnetic field.
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Affiliation(s)
- Tomoaki Miura
- Department of Chemistry, Faculty of Science, Shizuoka University, Ohya 836, Shizuoka City 422-8529, Japan
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35
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Rodgers CT, Norman SA, Henbest KB, Timmel CR, Hore PJ. Determination of radical re-encounter probability distributions from magnetic field effects on reaction yields. J Am Chem Soc 2007; 129:6746-55. [PMID: 17469816 DOI: 10.1021/ja068209l] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Measurements are reported of the effects of 0-23 mT applied magnetic fields on the spin-selective recombination of Py*- and DMA*+ radicals formed in the photochemical reaction of pyrene and N,N-dimethylaniline. Singlet <--> triplet interconversion in [Py*- DMA*+] radical pairs is probed by investigating combinations of fully protonated and fully deuterated reaction partners. Qualitatively, the experimental B1/2 values for the four isotopomeric radical pairs agree with predictions based on the Weller equation using known hyperfine coupling constants. The amplitude of the "low field effect" (LFE) correlates well with the ratio of effective hyperfine couplings, aDMA/aPy. An efficient method is introduced for calculating the spin evolution of [Py*- DMA*+] radical pairs containing a total of 18 spin-1/2 and spin-1 magnetic nuclei. Quantitative analysis of the magnetic field effects to obtain the radical re-encounter probability distribution f (t )-a highly ill-posed and underdetermined problem-is achieved by means of Tikhonov and maximum entropy regularization methods. The resulting f (t ) functions are very similar for the four isotopomeric radical pairs and have significant amplitude between 2 and 10 ns after the creation of the geminate radical pair. This interval reflects the time scale of re-encounters that are crucial for generating the magnetic field effect. Computer simulations of generalized radical pairs containing six spin-1/2 nuclei show that Weller's equation holds approximately only when the radical pair recombination rate is comparable to the two effective hyperfine couplings and that a substantial LFE requires, but is not guaranteed by, the condition that the two effective hyperfine couplings differ by more than a factor of 5. In contrast, for very slow recombination, essentially any radical pair should show a significant LFE.
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Affiliation(s)
- Christopher T Rodgers
- Contribution from the Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford, OX1 3QZ, United Kingdom
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36
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Kalneus EV, Stass DV, Ivanov KL, Molin YN. A MARY study of radical anions of fluorinated benzenes. Mol Phys 2006. [DOI: 10.1080/00268970600635438] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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37
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Verkhovlyuk VN, Morozov VA, Stass DV, Doktorov AB, Molin YUN. Experimental and theoretical study of spin evolution ‘switching on’ of the radical ion pair in MARY spectroscopy. Mol Phys 2006. [DOI: 10.1080/00268970600616313] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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38
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Henbest K, Maeda K, Athanassiades E, Hore P, Timmel C. Measurement of magnetic field effects on radical recombination reactions using triplet–triplet energy transfer. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.01.106] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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39
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The effect of signs of hyperfine coupling constant on MARY spectra affected by degenerate electron exchange. Chem Phys Lett 2005. [DOI: 10.1016/j.cplett.2005.07.042] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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40
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Indications for unequal rates of ion-molecular charge transfer reaction for biphenyl radical anion and cation from MARY and OD ESR spectra. Chem Phys Lett 2005. [DOI: 10.1016/j.cplett.2005.07.060] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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41
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Simonneaux G, Bondon A. Mechanism of Electron Transfer in Heme Proteins and Models: The NMR Approach. Chem Rev 2005; 105:2627-46. [PMID: 15941224 DOI: 10.1021/cr030731s] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Gérard Simonneaux
- Laboratoire de Chimie Organométallique et Biologique, UMR CNRS 6509, Institut de Chimie, Université de Rennes 1, France.
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42
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Ivanov KL, Lukzen NN, Doktorov AB. The integral encounter theory of multistage reactions containing association-dissociation reaction stages. III. Taking account of quantum states of reactants. J Chem Phys 2004; 121:5115-24. [PMID: 15352803 DOI: 10.1063/1.1783273] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The formalism developed in Part I [K. L. Ivanov, N. N. Lukzen, A. A. Kipriyanov, and A. B. Doktorov, Phys. Chem. Chem. Phys. 6, 1706 (2004)] of the present contribution is extended to treat the reacting particles with internal quantum states. Initial spatial correlations of reactants are considered in the framework of this formalism as well.
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