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YAGO Tomoaki
| Material Science Division | Associate Professor |
| Chemistry |
Researcher information
■ Research Keyword■ Field Of Study
■ Career
- Apr. 2022 - Present, Saitama University, Graduate School of Science and Engineering, associate professor, Japan
- Apr. 2007 - Mar. 2022, Saitama University, Graduate School of Science and Engineering, assistant professor, Japan
- Jan. 2006 - Mar. 2007, National Institute of Advanced Industrial Science and Technology (AIST), Research fellow, Japan
- Nov. 2003 - Dec. 2005, University of Freiburg, Department of physical chemistry, postdoctoral fellow, Germany
- Apr. 2003 - Oct. 2003, Semiconductor Research Foundation,, Semiconductor Research Institute, Japan
Performance information
■ Paper- Analytical model for spin dynamics in radical pairs under the spin-locking condition
Tomoaki Yago
The Journal of Chemical Physics, Jun. 2024, [Reviewed]
English, Scientific journal
DOI：https://doi.org/10.1063/5.0210982
DOI ID：10.1063/5.0210982, ISSN：0021-9606, ORCID：162625020 - Triplet–Triplet Annihilation via the Triplet Channel in Crystalline 9,10-Diphenylanthracene
Tomoaki Yago; Manami Tashiro; Kiichi Hasegawa; Masao Gohdo; Syuta Tsuchiya; Tadaaki Ikoma; Masanobu Wakasa
The Journal of Physical Chemistry Letters, Volume：13, Number：37, First page：8768, Last page：8774, Sep. 2022, [Reviewed]
American Chemical Society (ACS), Scientific journal
DOI：https://doi.org/10.1021/acs.jpclett.2c01839
DOI ID：10.1021/acs.jpclett.2c01839, ISSN：1948-7185, eISSN：1948-7185 - Singlet Fission in Solid 1,6-Diphenyl-1,3,5-hexatriene Dicarboxylic Acids and Esters: Effects of Meta and Para Substitution
Sonoda, Y.; Katoh, R.; Tohnai, N.; Yago, T.; Wakasa, M.
Journal of Physical Chemistry C, Volume：126, Number：20, 2022, [Reviewed]
Scientific journal
DOI：https://doi.org/10.1021/acs.jpcc.2c01474
DOI ID：10.1021/acs.jpcc.2c01474, ISSN：1932-7455, ORCID：118982417, SCOPUS ID：85130817952 - Low magnetic field effects on a photoinduced electron transfer reaction in an ionic liquid
Harada, N.; Matsuo, T.; Yago, T.; Maeda, K.; Wakasa, M.
Chemical Physics Letters, Volume：773, First page：138569, Last page：138569, Jun. 2021, [Reviewed]
Elsevier {BV}, English, Scientific journal
DOI：https://doi.org/10.1016/j.cplett.2021.138569
DOI ID：10.1016/j.cplett.2021.138569, ISSN：0009-2614, ORCID：92401171, SCOPUS ID：85103761543 - Initializing 214 Pure 14-Qubit Entangled Nuclear Spin States in a Hyperpolarized Molecular Solid
Gerd Kothe; Michail Lukaschek; Tomoaki Yago; Gerhard Link; Konstantin L. Ivanov; Tien-Sung Lin
The Journal of Physical Chemistry Letters, Volume：12, Number：14, First page：3647, Last page：3654, Apr. 2021, [Reviewed]
American Chemical Society ({ACS}), English, Scientific journal
DOI：https://doi.org/10.1021/acs.jpclett.1c00726
DOI ID：10.1021/acs.jpclett.1c00726, ISSN：1948-7185, ORCID：95380279, SCOPUS ID：85104370232 - Geminate delayed fluorescence by anisotropic diffusion-mediated reversible singlet fission and triplet fusion
Seki, K.; Yoshida, T.; Yago, T.; Wakasa, M.; Katoh, R.
Journal of Physical Chemistry C, Volume：125, Number：6, First page：3295, Last page：3304, Feb. 2021, [Reviewed]
American Chemical Society ({ACS}), Scientific journal
DOI：https://doi.org/10.1021/acs.jpcc.0c10582
DOI ID：10.1021/acs.jpcc.0c10582, ORCID：90660190, SCOPUS ID：85101935362 - Erratum: Low magnetic field effects on triplet pair annihilations at canonical orientations (J. Chem. Phys. (2019) 151 (214501) DOI: 10.1063/1.5127904)
T. Yago
Journal of Chemical Physics, Volume：153, Number：16, Oct. 2020
In our original manuscript,1 it was found that one term in the diagonal elements was omitted in the spin Hamiltonian of Eq. (7). The correct spin Hamiltonian is represented in the matrix form as follows: {equation presented} This correction affects the spin Hamiltonian of (B1a), the off-diagonal elements c+and c-in Eqs. (8) and (B1), and the spin wave functions of S' and Q'0in Eqs. (9) and (B2). These equations are corrected as follows: {equation presented} Fortunately, the coefficient of c+ in the original manuscript is almost the same as that in the corrected form. Thus, the above corrections have little effect on the conclusion and the calculated results in the original manuscript.
American Institute of Physics Inc., English, Scientific journal
DOI：https://doi.org/10.1063/5.0031228
DOI ID：10.1063/5.0031228, ISSN：1089-7690, PubMed ID：33138401, SCOPUS ID：85095403511 - Diffusion of Radical Ions in Ionic Liquids Having Long Alkyl Chains
Tsuchida, H.; Takeda, T.; Ishii, Y.; Yago, T.; Wakasa, M.
Journal of Physical Chemistry B, Volume：123, Number：40, 2019, [Reviewed]
Scientific journal
DOI：https://doi.org/10.1021/acs.jpcb.9b06007
DOI ID：10.1021/acs.jpcb.9b06007, ISSN：1520-5207, ORCID：89742182, SCOPUS ID：85073124117, Web of Science ID：WOS:000490354600011 - Low magnetic field effects on triplet pair annihilations at canonical orientations
Yago, T.
Journal of Chemical Physics, Volume：151, Number：21, 2019, [Reviewed]
Scientific journal
DOI：https://doi.org/10.1063/1.5127904
DOI ID：10.1063/1.5127904, ISSN：1089-7690, ORCID：89742198, SCOPUS ID：85076375861, Web of Science ID：WOS:000504066300025 - Exploring the Structure of an Exchange-Coupled Triplet Pair Generated by Singlet Fission in Crystalline Diphenylhexatriene: Anisotropic Magnetic Field Effects on Fluorescence in High Fields
Ishikawa, K.; Yago, T.; Wakasa, M.
Journal of Physical Chemistry C, Volume：122, Number：39, First page：22264, Last page：22272, Oct. 2018, [Reviewed]
Scientific journal
DOI：https://doi.org/10.1021/acs.jpcc.8b06026
DOI ID：10.1021/acs.jpcc.8b06026, ISSN：1932-7455, ORCID：89742166, SCOPUS ID：85053924092, Web of Science ID：WOS:000446926400005 - Structure and dynamics of triplet-exciton pairs generated from singlet fission studied via magnetic field effects
Wakasa, M.; Yago, T.; Sonoda, Y.; Katoh, R.
Communications Chemistry, Volume：1, Number：1, Mar. 2018, [Reviewed]
Scientific journal
DOI：https://doi.org/10.1038/s42004-018-0008-0
DOI ID：10.1038/s42004-018-0008-0, ISSN：2399-3669, ORCID：89742170, SCOPUS ID：85050869853, Web of Science ID：WOS:000433892800001 - A spin exchange model for singlet fission
Tomoaki Yago; Masanobu Wakasa
Chemical Physics Letters, Volume：695, First page：240, Last page：244, Mar. 2018, [Reviewed]
Singlet fission has been analyzed with the Dexter model in which electron exchange occurs between chromophores, conserving the spin for each electron. In the present study, we propose a spin exchange model for singlet fission. In the spin exchange model, spins are exchanged by the exchange interaction between two electrons. Our analysis with simple spin functions demonstrates that singlet fission is possible by spin exchange. A necessary condition for spin exchange is a variation in exchange interactions. We also adapt the spin exchange model to triplet fusion and triplet energy transfer, which often occur after singlet fission in organic solids.
Elsevier B.V., English, Scientific journal
DOI：https://doi.org/10.1016/j.cplett.2018.02.025
DOI ID：10.1016/j.cplett.2018.02.025, ISSN：0009-2614, SCOPUS ID：85042088892, Web of Science ID：WOS:000427386500038 - Singlet Fission in Fluorinated Diphenylhexatrienes
Ryuzi Katoh; Masaaki Hashimoto; Akinori Takahashi; Yoriko Sonoda; Tomoaki Yago; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY C, Volume：121, Number：46, First page：25666, Last page：25671, Nov. 2017, [Reviewed]
Experimentally determined quantum yields, decay profiles, and magnetic field effects on fluorescence showed that fluorinated derivatives of diphenylhexatriene were singlet fission materials. The rate constant of singlet fission was estimated as a function of temperature from the initial rate of decay of the fluorescence profiles. The origin of the temperature dependence was discussed in relation to the molecular stacking structure of the crystals.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/acs.jpcc.7b06905
DOI ID：10.1021/acs.jpcc.7b06905, ISSN：1932-7447, Web of Science ID：WOS:000416496200007 - Magnetic Field Effects on Triplet Pair Generated by Singlet Fission in an Organic Crystal: Application of Radical Pair Model to Triplet Pair
Tomoaki Yago; Kei Ishikawa; Ryuzi Katoh; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY C, Volume：120, Number：49, First page：27858, Last page：27870, Dec. 2016, [Reviewed]
Magnetic field effects (MFEs) on triplet pairs generated by singlet fission (SF) in an organic crystal, 1,6diphenyl-1,3,5-hexatriene, were studied by steady-state fluorescence measurements under ultrahigh magnetic fields of up to 10 T and by time-resolved fluorescence measurements with subnanosecond time resolution in the presence of magnetic field of 0.5 T. The observed MFEs were analyzed by using the stochastic Liouville equation based on the radical pair model with a modification of the spin Hamiltonian. Excellent agreements between the observed and the simulated MFEs demonstrate that the radical pair model used in the present study can apply to analysis of MFEs on triplet pairs generated by SF in organic materials. Model calculations were performed generated in the triplet pairs. The magnitude of the exchange from the observation of the MFE generated in the triplet pairs. The magnitude of the exchange from the observation of the MFE caused by the level crossing mechanism. We also determined the structure of the correlated triplet pair generated by the SF in 1,6-diphenyl-1,3,5-hexatriene crystal.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/acs.jpcc.6b09570
DOI ID：10.1021/acs.jpcc.6b09570, ISSN：1932-7447, Web of Science ID：WOS:000390072100014 - Photocyclization Reactions of Diarylethenes via the Excited Triplet State
Ryutaro Murata; Tomoaki Yago; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY A, Volume：119, Number：45, First page：11138, Last page：11145, Nov. 2015, [Reviewed]
Cyclization reactions of three diarylethene derivatives, 1,2-bis(2-methyl-3-benzothienyl)-perfluorocydopentene), and 2-bis2-isor (BTHex 1, (p opyl-3-perfluorocydopentene (BT), 1,2-bis(2-hexyl-3-benzothienyl)-benzothienyl)perfluorocydopentene (BTiPr), via their excited triplet states were studied by means of steady-state and nanosecond transient absorption spectroscopy. The excited triplet states of BT, BTHex, and BTiPr were generated by energy transfer from the photoexcited triplet states of sensitizers such as xanthone, phenanthrene, and pyrene. The single-step quantum yields of the cydization reactions from the excited triplet states of BT, BTHex, and BTiPr were determined to be 0.34, 0.53, and 0.65, respectively. The triplet energies of these three BTs were estimated to be 190-200 kJ mol(-1).
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/acs.jpca.5b08205
DOI ID：10.1021/acs.jpca.5b08205, ISSN：1089-5639, Web of Science ID：WOS:000364435300012 - What Can Be Learned from Magnetic Field Effects on Singlet Fission: Role of Exchange Interaction in Excited Triplet Pairs
Masanobu Wakasa; Mana Kaise; Tomoaki Yago; Ryuzi Katoh; Yusuke Wakikawa; Tadaaki Ikoma
JOURNAL OF PHYSICAL CHEMISTRY C, Volume：119, Number：46, First page：25840, Last page：25844, Nov. 2015, [Reviewed]
Magnetic field effects (MFEs) on singlet fission were studied by observing fluorescence from organic crystal of 1,6-diphenyl-1,3,5-hexatriene under magnetic fields of up to 5 T. We found anomalous MFE dips at magnetic fields higher than 2 T, in addition to the known MFEs which saturated around 1 T. The observed results were analyzed by using the stochastic Liouville equation (SLE) in which a distance-dependent exchange interaction (J) in triplet pair, hopping of triplet, and geminate fusion in contacted triplet pair were incorporated. The SLE analysis revealed that the observed dips were caused by a MFE due to the level crossing mechanism and strongly suggested that the contacted triplet pair has a large J, which has been ignored in the previous model of MFEs on the singlet fission. Present results lead to the conclusion that the initial dissociation of the singlet exciton to the contacted triplet pair does not show the MFE and the triplet pair at a separated distance produced by hopping of the triplet plays an important role on the generation of the MFE on the singlet fission
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/acs.jpcc.5b10176
DOI ID：10.1021/acs.jpcc.5b10176, ISSN：1932-7447, Web of Science ID：WOS:000365463000018 - Time-Resolved Detection of Magnetic Field Effects on Radical Pairs in Micelles: Two-Step Two-Laser Fluorescence Spectroscopy of Transient Radicals
Tomoaki Yago; Ayuto Takashino; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY C, Volume：119, Number：34, First page：20217, Last page：20223, Aug. 2015, [Reviewed]
A two-step two-laser fluorescence spectroscopy method was employed to enable time-resolved detection of magnetic field effects (MFEs) on radical pairs (RPs). In the photoinduced hydrogen abstraction reaction of benzophenone (BP) in sodium dodecyl sulfate (SDS) micellar solution, fluorescence from the BP ketyl radical (BPH center dot) was observed under various magnetic fields; BPH center dot forms RPs with hydrogen-abstracted SDS radicals (center dot SDS) in the micelles. Kinetic parameters of the RP dynamics such as the spin relaxation rate, the generation rate, and the escape rate were determined from the simple analysis. The MFEs on BPH center dot observed from the fluorescence measurements were explained by the spin relaxation mechanism proposed by Hayashi and Nagakura. In this study, we demonstrate that two-step two-laser fluorescence spectroscopy in combination with a magnetic field provides valuable information about photochemical reactions in which RPs play important roles.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/acs.jpcc.5b07524
DOI ID：10.1021/acs.jpcc.5b07524, ISSN：1932-7447, Web of Science ID：WOS:000360415700078 - Erratum: A practical approach to calculate the time evolutions of magnetic field effects on photochemical reactions in nano-structured materials(Phys. Chem. Chem. Phys. (2015) 10.1039/c5cp00595g)
Tomoaki Yago; Masanobu Wakasa
Physical Chemistry Chemical Physics, Volume：17, Number：18, First page：12366, May 2015, [Reviewed]
Royal Society of Chemistry, English, Scientific journal
DOI：https://doi.org/10.1039/c5cp90061a
DOI ID：10.1039/c5cp90061a, ISSN：1463-9076, SCOPUS ID：84928902428 - A practical approach to calculate the time evolutions of magnetic field effects on photochemical reactions in nano-structured materials
Tomoaki Yago; Masanobu Wakasa
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Volume：17, Number：15, First page：9737, Last page：9747, 2015, [Reviewed]
A practical method to calculate time evolutions of magnetic field effects (MFEs) on photochemical reactions involving radical pairs is developed on the basis of the theory of the chemically induced dynamic spin polarization proposed by Pedersen and Freed. In theory, the stochastic Liouville equation (SLE), including the spin Hamiltonian, diffusion motions of the radical pair, chemical reactions, and spin relaxations, is solved by using the Laplace and the inverse Laplace transformation technique. In our practical approach, time evolutions of the MFEs are successfully calculated by applying the Miller-Guy method instead of the final value theorem to the inverse Laplace transformation process. Especially, the SLE calculations are completed in a short time when the radical pair dynamics can be described by the chemical kinetics consisting of diffusions, reactions and spin relaxations. The SLE analysis with a short calculation time enables one to examine the various parameter sets for fitting the experimental date. Our study demonstrates that simultaneous fitting of the time evolution of the MFE and of the magnetic field dependence of the MFE provides valuable information on the diffusion motions of the radical pairs in nano-structured materials such as micelles where the lifetimes of radical pairs are longer than hundreds of nano-seconds and the magnetic field dependence of the spin relaxations play a major role for the generation of the MFE.
ROYAL SOC CHEMISTRY, English, Scientific journal
DOI：https://doi.org/10.1039/c5cp00595g
DOI ID：10.1039/c5cp00595g, ISSN：1463-9076, eISSN：1463-9084, Web of Science ID：WOS:000352270700017 - Diffusion and Solvation of Radical Ions in an Ionic Liquid Studied by the MFE Probe
Tomoaki Yago; Yuya Ishii; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY C, Volume：118, Number：38, First page：22356, Last page：22367, Sep. 2014, [Reviewed]
Magnetic field effects (MFEs) on photoinduced electron transfer reaction between benzophenone (BP) and 1,4-diazabicyclo [2.2.2] octane in an ionic liquid (IL) of N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) amide were studied by a nanosecond laser flash photolysis technique. The escape yield of the benzophenone radical anion (BP center dot-) was increased with increasing magnetic field strength (B) of 0 T < B <= 0.1 T and almost saturated at 0.1 T < B <= 1.7 T. The observed MFEs were explained by the hyperfine coupling mechanism (HFCM) and the relaxation mechanism (RM). The large MFEs indicate the nanometer-scaled cage effects on the diffusion of the radical ion pairs (RIP) generated by the photoinduced electron transfer reaction in TMPA TFSA. The cage lifetime for the RIP was estimated to be 170 ns, which is much longer than that previously reported for the neutral radical pairs (<20 ns) in the same IL. In addition to the large MFEs due to the HFCM and the RM, we also observed the MFE caused by the level crossing mechanism (LCM). These results suggest that compared with the neutral radicals, the radical ions are rigidly solvated in the IL and the nanometer-scaled charge-ordering structures are created around the radical ions.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp5069544
DOI ID：10.1021/jp5069544, ISSN：1932-7447, Web of Science ID：WOS:000342396300069 - Local structure of ionic liquids probed by self-quenching of thiobenzophenone
Miyuki Tanaka; Tomoaki Yago; Masanobu Wakasa
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Volume：15, Number：3, First page：787, Last page：794, 2013, [Reviewed]
Self-quenching of the triplet excited state of thiobenzophenone ((TBP)-T-3*) in molecular solvents, a sodium dodecyl sulfate (SDS) micellar solution, and ionic liquids (ILs) was measured using nanosecond laser flash photolysis. In the molecular solvents and ILs, (TBP)-T-3* single-exponentially decayed, and the decay was accelerated with increasing TBP concentration. Self-quenching rate constants (k(SQ)) obtained in the ILs were smaller than those in the molecular solvents with similar solvent viscosities, indicating that molecular diffusion is inhibited in the ILs. In the SDS micellar solution, the decay of (TBP)-T-3* showed two components. The fast decay component was attributed to self-quenching of (TBP)-T-3* which presents inside micelles containing two or more TBP molecules, while the slow decay component was from deactivation of single (TBP)-T-3*. The decay of (TBP)-T-3* in an IL, N, N, N-trimethyl-N-propylammonium bis(trifluoromethylsulfonyl) amide (TMPA TFSA), had only one decay component, showing that unlike the micelles, the local structure of TMPA TFSA does not have a long lifetime. The cage lifetime of TMPA TFSA was estimated to be between 17 and 20 ns.
ROYAL SOC CHEMISTRY, English, Scientific journal
DOI：https://doi.org/10.1039/c2cp42766d
DOI ID：10.1039/c2cp42766d, ISSN：1463-9076, Web of Science ID：WOS:000312217200008 - Cage lifetimes of ionic liquids as studied by the magnetic field effect probe
Tomohide Okada; Tomoaki Yago; Tadashi Takamasu; Masanobu Wakasa
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Volume：14, Number：10, First page：3490, Last page：3497, 2012, [Reviewed]
Magnetic field effects (MFEs) on the photoinduced hydrogen abstraction reaction of benzophenone with phenol were investigated in ionic liquids (ILs) with a short alkyl chain (N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) amide (TMPA TFSA)) and long alkyl chains ((N, N, N-trimethyl-N-octylammonium bis(trifluoromethanesulfonyl) amide (TMOA TFSA) and N-decyl-N,N,N-trimethylammonium bis(trifluoromethanesulfonyl) amide (DTMA TFSA)) by a nanosecond laser flash photolysis technique. In each ionic liquid, escaped radical yield of a benzophenone ketyl radical rapidly increased with increasing magnetic field strength (B) of < T o B <= 0.01 T < At 0.01 T < B <= 0.4 T, the escaped radical yield almost saturated in TMPA TFSA or gradually increased in TMOA TFSA and DTMA TFSA. At much higher fields of 0.4 T < B <= 30 T, the yield gradually decreased, resulting in 10-15% decrease at 30 T. The observed MFEs can be explained by the hyperfine coupling and Dg mechanisms together with the relaxation mechanism. On the time profiles of the transient absorption observed for the benzophenone ketyl radical, MFEs were generated in the time range of 0 < t < 0.6 ms. The cage lifetimes of TMOA TFSA and DTMA TFSA were estimated to be at least 120 ns.
ROYAL SOC CHEMISTRY, English, Scientific journal
DOI：https://doi.org/10.1039/c2cp23747d
DOI ID：10.1039/c2cp23747d, ISSN：1463-9076, eISSN：1463-9084, Web of Science ID：WOS:000300314100026 - Cyclization Reaction of Diarylethene through the Triplet Excited State
Ryutaro Murata; Tomoaki Yago; Masanobu Wakasa
BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, Volume：84, Number：12, First page：1336, Last page：1338, Dec. 2011, [Reviewed]
Photocyclization reaction of 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BT) in methanol was studied by using nanosecond laser flash photolysis at 296 K. When xanthone was used as a triplet sensitizer, the triplet energy transfer occurred efficiently and the closed-ring product of BT was observed.
CHEMICAL SOC JAPAN, English, Scientific journal
DOI：https://doi.org/10.1246/bcsj.20110212
DOI ID：10.1246/bcsj.20110212, ISSN：0009-2673, eISSN：1348-0634, Web of Science ID：WOS:000298906900005 - Magnetic Field Effects on Photochemical Reactions in Ionic Liquids with Short Alkyl Chains
Tomoaki Yago; Atom Hamasaki; Miyuki Tanaka; Tadashi Takamasu; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY C, Volume：115, Number：43, First page：21063, Last page：21071, Nov. 2011, [Reviewed]
Magnetic field effects (MFEs) on the photoinduced hydrogen abstraction reactions of benzophenone and thiobenzophenone from thiophenol were investigated in several ionic liquids with short alkyl chains by a nanosecond laser flash photolysis technique. In each ionic liquid, escaped radical yields of benzophenone and thiobenzophenone ketyl radicals gradually decreased with increasing magnetic field strength. The observed results were analyzed by using the stochastic Liouville equation (SLE), employing a solvent separated radical pair (SSRP) model where the SSRP with a specific radical-radical distance is stable and has a long lifetime. The SLE analysis revealed that the lifetime of the SSRP and the radical rotation in the SSRP states are strongly correlated with the macroviscosity of the ionic liquids.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp207816t
DOI ID：10.1021/jp207816t, ISSN：1932-7447, Web of Science ID：WOS:000296172800033 - Magnetic Field Effects on Hydrogen Abstraction of Thiobenzophenone as a Probe of Microviscosity
Miyuki Tanaka; Tomoaki Yago; Yoshio Sakaguchi; Tadashi Takamasu; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY B, Volume：115, Number：9, First page：1936, Last page：1943, Mar. 2011, [Reviewed]
Hydrogen abstraction reactions of thiobenzophenone with thiophenol in solutions of varying viscosities (eta = 0.29-42.0 cP) were studied by a nanosecond laser flash photolysis under magnetic fields of 0-15.5 T. In alcoholic solutions, the escaped radical yield (Y) of thiobenzophenone ketyl radical showed appreciable magnetic field effects (MFEs). The observed MFEs can be interpreted with the Delta g mechanism through the triplet radical pair. The relative escaped radical yield (R(1.7T) = Y(1.7T)/Y(0T)) decreased with increasing eta at 0 < eta <= 3.33 cP, but then the yield increased with increasing eta at 3.33 cP <eta <= 2.22 cP. At much higher viscosity, 22.2 cP < eta <= 42 cP, R(1.7T) values become 1.0 within experimental errors. Such quenching of MFE was explained by the spin- orbit coupling recombination of close radical pairs associated with high viscosity. The MFEs on the present reaction is extremely sensitive to the solvent viscosity in the vicinity of the radical pairs. Using this probe reaction, microviscosities of sodium dodecyl sulfate (SDS) and Brij35 micellar solutions were estimated.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp108898a
DOI ID：10.1021/jp108898a, ISSN：1520-6106, Web of Science ID：WOS:000287833000002 - Nanoscale Structure of Ionic Liquid and Diffusion Process as Studied by the MFE Probe
Tomoaki Yago; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY C, Volume：115, Number：6, First page：2673, Last page：2678, Feb. 2011, [Reviewed]
Magnetic field effects (MFEs) observed for photoinduced hydrogen abstract reaction between benzophenone and thiophenol, generating phenylthiyl and benzophenone ketyl radicals, in an ionic liquid of N,N,N,-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide (TMPA TFSA) were analyzed by using the stochastic Liouville equation (SLE) with the cage model and the solvent separated radical pair model, respectively. The MFEs observed on the yield of escaped benzophenone ketyl radical in the range of 0 < B <= 2.0 T were explained by the transverse spin relaxation in the radical pair caused by the large anisotropy of the g-value and the slow rotation of phenylthiyl radical in the IL. The calculated MFE was dependent on a rotational correlation time of the radical as well as the mutual diffusion coefficient for the translational diffusion of the radicals. The SLE analysis revealed that the IL has at least two different viscosity regions, causing the nanoscale cage effect on the radical diffusion in the IL.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp1108762
DOI ID：10.1021/jp1108762, ISSN：1932-7447, Web of Science ID：WOS:000287065700010 - Magnetic Field Effects on Photochemical Reaction in Mesoporous Silicates of MCM-41 under High Magnetic Fields up to 5 T
Tomoaki Maeyama; Hiroki Matsui; Tomoaki Yago; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY C, Volume：114, Number：50, First page：22190, Last page：22196, Dec. 2010, [Reviewed]
Magnetic field effects (MFEs) on photoinduced hydrogen abstraction reaction of xanthone with xanthene were investigated in 2-propanol confined in mesoporous silicates of MCM-41 under high magnetic fields up to 5 T. The observed MFEs were explained by the spin relaxation mechanism associated with the cage effects on diffusion of the radical pairs in nanopores of MCM-41. The qualitative analysis using the stochastic Liouville equation revealed that the motions of the radical pairs are not restricted in the one dimension, although the MCM-41 used in the present study has the one-dimensional pore with the diameter of 1.7 or 2.7 nm. The effective viscosities for rotation of the solute molecule in the pores were estimated to be 5-10 cP.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp107729s
DOI ID：10.1021/jp107729s, ISSN：1932-7447, Web of Science ID：WOS:000285236800042 - Quantum Oscillations and Polarization of Nuclear Spins in Photoexcited Triplet States
Gerd Kothe; Tomoaki Yago; Jorg-Ulrich Weidner; Gerhard Link; Michail Lukaschek; Tien-Sung Lin
JOURNAL OF PHYSICAL CHEMISTRY B, Volume：114, Number：45, First page：14755, Last page：14762, Nov. 2010, [Reviewed]
The unique physical properties of photoexcited triplet states have been explored in numerous spectroscopic studies employing electron paramagnetic resonance (EPR) So far, however, no quantum interference effects were found in these systems in the presence of a magnetic field In this study, we report the successful EPR detection of nuclear quantum oscillations in an organic triplet state subject to an external magnetic field The observed quantum coherences can be rationalized using an analytical theory Analysis suggests that the nuclear spins are actively involved in the intersystem crossing process The novel mechanism also acts as a source of oscillatory nuclear spin polarization that gives rise to large signal enhancement in nuclear magnetic resonance (NMR) This opens new perspectives for the analysis of chemically induced dynamic nuclear polarization in mechanistic studies of photoactive proteins
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp103508t
DOI ID：10.1021/jp103508t, ISSN：1520-6106, Web of Science ID：WOS:000284018000078 - Hydrogen Bonding Effects on the Reorganization Energy for Photoinduced Charge Separation Reaction between Porphyrin and Quinone Studied by Nanosecond Laser Flash Photolysis
Tomoaki Yago; Masao Gohdo; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY B, Volume：114, Number：7, First page：2476, Last page：2483, Feb. 2010, [Reviewed]
Alcohol concentration dependences of photoinduced charge separation (CS) reaction of zinc tetraphenylporphyrin (ZnTPP) and duroquinone (DQ) were investigated in benzonitrile by a nanosecond laser flash photolysis technique. The photoinduced CS reaction was accelerated by the addition of alcohols, whereas the addition of acetonitrile caused little effect on the CS reactions. The simple theory was developed to calculate an increase in reorganization energies induced by the hydrogen bonding interactions between DQ and alcohols using the chemical equilibrium constants for the hydrogen bonding complexes through the concerted pathway and the stepwise one. The experimental results were analyzed by using the Marcus equation where we took into account the hydrogen bonding effects on the reorganization energy and the reaction free energy for the CS reaction. The observed alcohol concentration dependence of the CS reaction rates was well explained by the formation of the hydrogen bonding complexes through the concerted pathway, demonstrating the increase in the reorganization energy by the hydrogen bonding interactions.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp909927w
DOI ID：10.1021/jp909927w, ISSN：1520-6106, Web of Science ID：WOS:000274578500019 - Primary Photochemical Process of Thiobenzophenone as Studied by Laser Flash Photolysis
Miyuki Tanaka; Tomoaki Yago; Masanobu Wakasa
CHEMISTRY LETTERS, Volume：38, Number：11, First page：1086, Last page：1087, Nov. 2009, [Reviewed]
Self-quenching of the triplet excited state of thiobenzophenone (TBP) was suppressed in a viscous alcoholic solution, an SDS micellar solution and an ionic liquid of TMPA TFSA. In those Solutions, the photochemical primary process of TBP could be studied by ns laser flash photolysis. Thiobenzophenone ketyl and phenylsulfanyl radicals were found to be generated from hydrogen abstraction of benzenethiol by TBP. The rate constant for the reaction was observed to be 1.1 x 10(7) s(-1) mol(-1) dm(3).
CHEMICAL SOC JAPAN, English, Scientific journal
DOI：https://doi.org/10.1246/cl.2009.1086
DOI ID：10.1246/cl.2009.1086, ISSN：0366-7022, eISSN：1348-0715, Web of Science ID：WOS:000272854200037 - Ethanol Concentration Dependence of Photoinduced Charge Separation Reaction between Zinc Tetraphenylporphyrin and Duroquinone Studied by Laser Flash Photolysis
Tomoaki Yago; Masao Gohdo; Masanobu Wakasa
CHEMISTRY LETTERS, Volume：38, Number：9, First page：880, Last page：881, Sep. 2009, [Reviewed]
Ethanol concentration dependence of photoinduced charge separation between zinc tetraphenylporphyrin (ZnTPP) and duroquinone (DQ) in benzonitrile was studied by nanosecond laser flash photolysis. Acceleration of the photoinduced charge separation reaction rate by hydrogen bonding between DQ anion radical and ethanol was observed. A simple analysis in the framework of the Marcus theory indicated that the observed electron-transfer reaction rate was affected not only by the decrease of the reaction free energy but also an increase of the reorganization energy in the presence of hydrogen bonding.
CHEMICAL SOC JAPAN, English, Scientific journal
DOI：https://doi.org/10.1246/cl.2009.880
DOI ID：10.1246/cl.2009.880, ISSN：0366-7022, eISSN：1348-0715, Web of Science ID：WOS:000270590500004 - Nanoscale Heterogeneous Structure of Ionic Liquid as Revealed by Magnetic Field Effects
Masanobu Wakasa; Tomoaki Yago; Atom Hamasaki
JOURNAL OF PHYSICAL CHEMISTRY B, Volume：113, Number：31, First page：10559, Last page：10561, Aug. 2009, [Reviewed]
Large magnetic field effects (MFEs) observed for photoinduced hydrogen abstraction reaction between benzophenone and thiophenol in an ionic liquid (N,N,N,-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide, TMPA TFSA) are analyzed by using the stochastic Liouville equation for the first time. The sphere cage model can well reproduce the observed MFEs and the nanoscale heterogeneous structure with a cage radius of 1.8 +/- 0.3 nm, and an effective viscosity in the cage of 1-2 cP is found to be formed in TMPA TFSA.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp905543k
DOI ID：10.1021/jp905543k, ISSN：1520-6106, Web of Science ID：WOS:000268479000004 - Magnetic Field Effect on a Radical Pair Reaction as a Probe of Microviscosity
Atom Hamasaki; Tomoaki Yago; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY B, Volume：112, Number：45, First page：14185, Last page：14192, Nov. 2008, [Reviewed]
The magnetic field effects (MFEs), caused by the Delta g mechanism, on the pehotoinduced hydrogen abstraction reaction of benzopheneone with thiophenol were investigated in alcoholic solutions of varying viscosities (eta = 0.55 to 59.2 cP) by a nanosecond laser flash photolysis technique. The escape yield of benzophenone ketyl radicals (Y) gradually decreased with increasing magnetic field strength (B) from 0 to 1.6 T. The relative yield observed at 1.6 T, R(1.6 T) = Y(1.6 T)/Y(0 T), decreased with increasing eta in the range of 0.55 cP <= eta <= 5 cP, and then increased with increasing eta in the range of 5 cP < eta <= 55.3 cP. When eta was higher than 55.3 cP, the R(1.6 T) value became 1.0, and MFEs were completely quenched. The observed eta dependence of the MFEs was analyzed by the stochastic Liouville equation (SLE), in which the effects of spin-orbit coupling by a heavy atom such as sulfur were taken into account. The observed MFEs were reproduced fairly well by the SLE analysis. The diffusion coefficients of the radicals obtained by the SLE were about three times smaller than those expected from the macroscopic solvent viscosities. One can probe the microviscosity in the vicinity of the radical pairs by observing MFEs on the present photochemical reaction system.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp804862w
DOI ID：10.1021/jp804862w, ISSN：1520-6106, CiNii Articles ID：80019963904, PubMed ID：18939791, SCOPUS ID：57049142078, Web of Science ID：WOS:000260675800013 - Formation process of micrometer-sized pseudoisocyanine J-aggregates studied by single-aggregate fluorescence spectroscopy
Yasutaka Kitahama; Tomoaki Yago; Akihiro Furube; Ryuzi Katoh
CHEMICAL PHYSICS LETTERS, Volume：457, Number：4-6, First page：427, Last page：433, May 2008, [Reviewed]
We have studied the formation process of pseudoisocyanine (PIC) J-aggregates by fluorescence detection of single aggregates in. owing solution. After the addition of sodium chloride as the initiator for aggregation, both continuous and pulse-like signals were observed. The continuous signal is the fluorescence of a large amount of 'meso-aggregates' consisting of 20-100 PIC molecules each. The pulsed signal is the fluorescence of individual 'macro-aggregates' of micrometer lengths. We discuss the formation process of these macro-aggregates on the basis of the temporal behavior observed. (C) 2008 Elsevier B.V. All rights reserved.
ELSEVIER SCIENCE BV, English, Scientific journal
DOI：https://doi.org/10.1016/j.cplett.2008.04.021
DOI ID：10.1016/j.cplett.2008.04.021, ISSN：0009-2614, eISSN：1873-4448, Web of Science ID：WOS:000255953800030 - Anomalous magnetic field effects on photochemical reactions in ionic liquid under ultrahigh fields of up to 28 T
Atom Hamasaki; Tomoaki Yago; Tadashi Takamasu; Giyuu Kido; Masanobu Wakasa
JOURNAL OF PHYSICAL CHEMISTRY B, Volume：112, Number：11, First page：3375, Last page：3379, Mar. 2008, [Reviewed]
The magnetic field effects (MFEs) on photoinduced hydrogen abstraction reactions between benzophenone and thiophenol in an ionic liquid, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) imide (TMPA TFSI), were studied by a nanosecond laser flash photolysis technique under ultrahigh fields of up to 28 T. Extremely large and anomalous stepwise MFEs were observed for the first time. The escape yield of benzophenone ketyl radical decreased with increasing magnetic field strength (B) at 0 T < B <= 2 T. The decrease was almost saturated at 2 T < B <= 10 T. At much higher fields (10 T < B <= 28 T), the yield decreased again with increasing B, producing a 25% decrease at 28 T.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp710047c
DOI ID：10.1021/jp710047c, ISSN：1520-6106, CiNii Articles ID：80019421159, PubMed ID：18298111, SCOPUS ID：46749112239, Web of Science ID：WOS:000253945900016 - Imaging of exciton absorption in perylene crystals by femtosecond-laser scanning microscopy
Tomoaki Yago; Yoshiaki Tamaki; Akihiro Furube; Ryuzi Katoh
JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：47, Number：2, First page：1400, Last page：1403, Feb. 2008, [Reviewed]
The density of excitons, which depends on the local structure of perylene organic crystals, was imaged by femtosecond-laser scanning microscopy. By a two-photon process, a desired position of a single perylene crystal was excited selectively in a three-dimensional space. The resulting excitons were subsequently detected by probing the transient absorption. By using two-dimensional transient absorption images constructed with thousands of data points, we have visualized the density of the excitons generated in perylene crystals with a micrometer spatial resolution and a time resolution of several hundred femtoseconds.
JAPAN SOC APPLIED PHYSICS, English, Scientific journal
DOI：https://doi.org/10.1143/JJAP.47.1400
DOI ID：10.1143/JJAP.47.1400, ISSN：0021-4922, CiNii Articles ID：150000050047, SCOPUS ID：54249148973, Web of Science ID：WOS:000255020000055 - Self-trapping limited exciton diffusion in a monomeric perylene crystal as revealed by femtosecond transient absorption microscopy
Tomoaki Yago; Yoshiaki Tamaki; Akihiro Furube; Ryuzi Katoh
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Volume：10, Number：30, First page：4435, Last page：4441, 2008, [Reviewed]
Self-trapping and singlet-singlet annihilation of the free excitons in a monomeric (b) perylene crystal were studied by using femtosecond transient absorption microscopy. The free exciton generated by the photo-excitation of the beta-perylene crystal relaxed to the self-trapped exciton with a rate constant of 7 x 10(10) s(-1). The singlet-singlet annihilation of the free exciton observed under the high excitation density conditions was competed with the self-trapping of the free exciton; we estimated the annihilation rate constant for the free exciton to be 1 x 10(-8) cm(3) s(-1) from the excitation density dependence of the free exciton decay. After self-trapping of the free exciton, no annihilation was observed in the 100 ps time range, suggesting that the diffusion coefficient was reduced drastically by self-trapping. The results show that the major factor limiting the exciton diffusion in the beta-perylene crystal is a relaxation of the free exciton to the self-trapped exciton, and not the lifetime of the exciton. Though the singlet-singlet annihilation rate constants and fluorescence lifetime of the beta-perylene crystal are similar to those of the anthracene crystal, the estimated exciton diffusion length (2 nm) in the beta-perylene crystal is much smaller than that (100 nm) in the anthracene crystal as a result of the exciton self-trapping.
ROYAL SOC CHEMISTRY, English, Scientific journal
DOI：https://doi.org/10.1039/b801856a
DOI ID：10.1039/b801856a, ISSN：1463-9076, Web of Science ID：WOS:000257889600010 - Pulsed electron nuclear double resonance studies of the photoexcited triplet state of pentacene in p-terphenyl crystals at room temperature
Tomoaki Yago; Gerhard Link; Gerd Kothe; Tien-Sung Lin
JOURNAL OF CHEMICAL PHYSICS, Volume：127, Number：11, Sep. 2007, [Reviewed]
Pulsed electron nuclear double resonance (ENDOR) using a modified Davies-type [Phys. Lett. 47A, 1 (1974)] sequence is employed to study the hyperfine (HF) structure of the photoexcited triplet state of pentacene dispersed in protonated and deuterated p-terphenyl single crystals. The strong electron spin polarization and long phase memory time of triplet pentacene enable us to perform the ENDOR measurements on the S=1 spin system at room temperature. Proton HF tensor elements and spin density values of triplet pentacene are extracted from a detailed angular-dependent study in which the orientation of the magnetic field is varied systematically in two different pentacene planes. Analysis reveals that the pentacene molecule is no longer planar in the p-terphenyl host lattice. The distortion is more pronounced in the deuterated crystal where the unit cell dimensions are slightly smaller than those of the protonated crystal. (c) 2007 American Institute of Physics.
AMER INST PHYSICS, English, Scientific journal
DOI：https://doi.org/10.1063/1.2771145
DOI ID：10.1063/1.2771145, ISSN：0021-9606, Web of Science ID：WOS:000249667400038 - Quantum oscillations in photo-excited triplet states in an external magnetic field
Tomoaki Yago; Joerg-Ulrich Weidner; Gerhard Link; Tien-Sung Lin; Gerd Kothe
CHEMICAL PHYSICS LETTERS, Volume：438, Number：4-6, First page：351, Last page：357, Apr. 2007, [Reviewed]
Using the density operator formalism, an analytical model is developed to study the time evolution of the electron spin magnetization of photo-excited triplet states in an external magnetic field. Analysis reveals that pulsed light excitation initiates an oscillatory electron spin magnetization in the direction of the external field. The frequency of the quantum oscillations is determined by the electron Zeeman and dipolar interactions. The oscillation amplitude reaches a maximum when the electron Zeeman splitting matches the energy of a zero-field transition of the triplet state. This suggests that the predicted quantum oscillations can be detected only at low magnetic fields. (c) 2007 Elsevier B.V. All rights reserved.
ELSEVIER SCIENCE BV, English, Scientific journal
DOI：https://doi.org/10.1016/j.cplett.2007.03.031
DOI ID：10.1016/j.cplett.2007.03.031, ISSN：0009-2614, Web of Science ID：WOS:000246060000039 - Growth of beta-perylene crystal
Tomoaki Yago; Yoshiaki Tamaki; Akihiro Furube; Ryuzi Katoh
CHEMISTRY LETTERS, Volume：36, Number：3, First page：370, Last page：371, Mar. 2007, [Reviewed]
Although perylene crystals have been known to show both dimeric (alpha) and monomeric (beta) phases, to date only the stable a-crystals have been obtained under conventional conditions. Here, we propose a procedure for the selective growth of phase perylene crystals, in which a saturated toluene solution at 350K was cooled to 298K with a high cooling rate (-30K/min). The sizes of beta-phase crystals obtained were in the order of 100 mu m.
CHEMICAL SOC JAPAN, English, Scientific journal
DOI：https://doi.org/10.1246/cl.2007.370
DOI ID：10.1246/cl.2007.370, ISSN：0366-7022, eISSN：1348-0715, Web of Science ID：WOS:000246058000010 - Structural organization in photosynthetic proteins as studied by high-field EPR of spin-correlated radical pair states
G Link; OG Poluektov; LM Utschig; J Lalevee; T Yago; JU Weidner; MC Thurnauer; G Kothe
MAGNETIC RESONANCE IN CHEMISTRY, Volume：43, First page：S103, Last page：S109, Nov. 2005, [Reviewed]
We demonstrate the potential of high-field (HF) time-resolved electron paramagnetic resonance (EPR) spectroscopy to reveal unique information about electron transfer processes and the structure of photosynthetic systems. The lineshapes and electron spin polarization (ESP) of spin-correlated radical pair (SCRP) spectra recorded with HF-EPR are very sensitive to the magnetic parameters, interactions, and geometry of the radicals in the pair. This sensitivity facilitates an analysis of more sophisticated models and methods to reveal the important relationship between structural organization and light-induced electron transfer of the photosynthetic proteins. In this review, we report on a new time-resolved HF and multi-frequency EPR approach developed in the Freiburg laboratory in cooperation with the Argonne Photosynthesis group. The method is designed to probe the geometric structure of charge separated states in the photosynthetic membrane. First, we discuss the magneto-orientation of photosynthetic cyanobacteria as revealed by time-resolved HF-EPR of SCRPs. Then, we demonstrate how the three-dimensional structure of the SCRP P-700(+) A(1)(-) from photosystem I of oxygenic photosynthesis and its arrangement in the membrane is obtained from application of multi-frequency including time-resolved HF-EPR techniques. Copyright (c) 2005 John Wiley & Sons, Ltd.
WILEY-BLACKWELL, English, Scientific journal
DOI：https://doi.org/10.1002/mrc.1678
DOI ID：10.1002/mrc.1678, ISSN：0749-1581, eISSN：1097-458X, PubMed ID：16235208, SCOPUS ID：27644590846, Web of Science ID：WOS:000233024800013 - Correlation field splitting of intramolecular vibrations of crystalline tetracene in terahertz region
T Yago; Y Ishikawa; H Ito; H Tanaka; E Kwon; K Sakamoto; K Suto; M Watanabe; J Nishizawa
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, Volume：44, Number：6A, First page：4145, Last page：4150, Jun. 2005, [Reviewed]
The temperature dependence of terahertz (THz) absorption was observed for molecular crystals of tetracene using the Fourier transform infrared (FT-IR) spectroscopy. Over the frequency range of I to 6THz (33 to 200cm(-1)), THz absorptions corresponding to phonon and intramolecular vibrational modes were confirmed. Furthermore, the intramolecular vibrational modes exhibited correlation field splitting that originated from crystallization. A temperature-induced phase transition was successfully detected for the intramolecular vibrational modes of tetracene, even in powder form. Our results showed that these THz absorptions are highly sensitive to the molecular orientations within the crystal.
JAPAN SOC APPLIED PHYSICS, English, Scientific journal
DOI：https://doi.org/10.1143/JJAP.44.4145
DOI ID：10.1143/JJAP.44.4145, ISSN：0021-4922, SCOPUS ID：23944445266, Web of Science ID：WOS:000230126000102 - Aspects of the electron transfer reaction rate for systems accompanying a chemical equilibrium change
T Yago; Y Kobori; K Akiyama; S Tero-Kubota
BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, Volume：77, Number：11, First page：1997, Last page：2001, Nov. 2004, [Reviewed]
In photoinduced electron-transfer systems accompanying chemical equilibrium changes, such as the formation/dissociation of a noncovalent-bonded complex, the calculation method of the charge separation and recombination reaction rates have been derived based on a simple model, in which the formation /dissociation of noncovalent bonding during the electron-transfer reaction is treated as a change of the chemical equilibrium. The effects of the formation /dissociation of noncovalent bonding on the driving forces and the reorganization energies were calculated using the chemical equilibrium constants for the reactant and product states. It has been demonstrated that the formation/dissociation of noncovalent bonding affects the electron-transfer reaction rates not only by stabilizing the charge- separated state, but also by increasing the reorganization energy.
CHEMICAL SOC JAPAN, English, Scientific journal
DOI：https://doi.org/10.1246/bcsj.77.1997
DOI ID：10.1246/bcsj.77.1997, ISSN：0009-2673, eISSN：1348-0634, SCOPUS ID：9744268198, Web of Science ID：WOS:000225482300004 - Superexchange electron tunneling mediated by solvent molecules: Pulsed electron paramagnetic resonance study on electronic coupling in solvent-separated radical ion pairs
Y Kobori; T Yago; K Akiyama; S Tero-Kubota; H Sato; F Hirata; Norris, JR
JOURNAL OF PHYSICAL CHEMISTRY B, Volume：108, Number：29, First page：10226, Last page：10240, Jul. 2004, [Reviewed]
Nanosecond pulsed electron paramagnetic resonance spectroscopy is applied to characterize exponential decay constants (beta) of the squared electronic coupling matrix element (V-DA(2)) in transient, solvent-separated radical ion pairs (RIP) composed of quinone anions and several cation radicals in aprotic liquid solutions of N,N-dimethylformamide, DMSO, and benzonitrile. The distance dependence of singlet-triplet energy splitting (2J) is shown to be described by beta in V-DA for charge-recombination processes. We show that the radical pair mechanism (RPM) electron spin polarization (P-RPM) is quite sensitive to beta. The beta value is characterized by using the stochastic Liouville equation to fit the experimental P-RPM values. The beta values (from 0.8 to 1.0 Angstrom(-1)) manifest that V-DA is governed by the superexchange mechanism mediated by the intervening solvent molecules from a result that the beta increases with increasing the tunneling energy gap (DeltaG(eff)) for solvent oxidation or reduction in several intermolecular electron-transfer systems. We propose a simple three-dimensional model of V-DA, in which the through-solvent tunneling pathways are exponentially increased with the increase in the intermolecular distance in bulk, condensed media. This model explains the DeltaG(eff) dependence of beta, including the data previously reported on the charge-transfer reactions both in liquid and frozen (77 K) solutions. Effective solvent-solvent coupling is estimated to be v(B) approximate to 850 cm(-1) at a mean nearest-neighbor distance of 5.7 Angstrom. This relatively large magnitude of v(B) may agree with dynamical amplifications of the effective coupling by low-frequency motions of the mediators as reported in charge-transfer reactions in biological systems.
AMER CHEMICAL SOC, English
DOI：https://doi.org/10.1021/jp036925t
DOI ID：10.1021/jp036925t, ISSN：1520-6106, SCOPUS ID：3442901077, Web of Science ID：WOS:000222763000004 - Control of the sign of exchange interactions in solvent-separated radical ion pairs
S Tero-Kubota; K Zikihara; T Yago; Y Kobori; K Akiyama
APPLIED MAGNETIC RESONANCE, Volume：26, Number：1-2, First page：145, Last page：154, 2004, [Reviewed]
The chemically induced dynamic electron polarization spectra generated by the laser photolysis of several donor-acceptor systems have been studied to verify the solvent effects on the exchange interaction in solvent-separated radical ion pairs. It has been shown that the sign of the exchange interaction depends on the polarity of solvents. The individual reorganization energies have been determined for several solvent-separated radical ion pair systems.
SPRINGER WIEN, English, Scientific journal
DOI：https://doi.org/10.1007/BF03166568
DOI ID：10.1007/BF03166568, ISSN：0937-9347, eISSN：1613-7507, SCOPUS ID：3042701871, Web of Science ID：WOS:000222366000011 - Reorganization energy induced by noncovalent bonding interaction in electron transfer reactions
T Yago; Y Kobori; K Akiyama; S Tero-Kubota
JOURNAL OF PHYSICAL CHEMISTRY B, Volume：107, Number：48, First page：13255, Last page：13257, Dec. 2003, [Reviewed]
A simple model is proposed to calculate a component of the electron-transfer reorganization energy derived from the reversible process of noncovalnt bond formation/dissociation between the reactant and hydrogen bonding donor or ligand. In the model, the reorganization of the formation/dissociation of the noncovalent-bonded complex is estimated by considering the chemical equilibrium change during the electron-transfer reaction. The effects of the hydrogen bonding and the ligand binding on the reorganization energies are calculated for the one-electron reduction processes of quinones, flavin, and the hem-fragment of cytochrome c based on the formation/dissociation constants of the noncovalent-bonded complexes in the liquid phase.
AMER CHEMICAL SOC, English
DOI：https://doi.org/10.1021/jp035494b
DOI ID：10.1021/jp035494b, ISSN：1520-6106, SCOPUS ID：0346947219, Web of Science ID：WOS:000186878000002 - Time-resolved EPR study on reorganization energies for charge recombination reactions in the systems involving hydrogen bonding
T Yago; Y Kobori; K Akiyama; S Tero-Kubota
CHEMICAL PHYSICS LETTERS, Volume：369, Number：1-2, First page：49, Last page：54, Feb. 2003, [Reviewed]
Hydrogen bonding effects on reorganization energies (lambda) in the photoinduced electron donor-acceptor system of duroquinone (DQ)-1,2,4-trimethoxybenzene (TMB) in benzonitrile have been investigated by time-resolved EPR and cyclic voltammetry measurements. The solvent reorganization energies (lambda(S)) determined for the radical ion pair systems involving the hydrogen-bonded complexes are larger by similar to0.2 eV than those calculated from the Marcus continuum dielectric model. The present results suggest that dissociation of the DQ anion-alcohol hydrogen-bonded complex results in the new component of As for the charge recombination reaction in polar solvents. (C) 2003 Elsevier Science B.V. All rights reserved.
ELSEVIER SCIENCE BV, English, Scientific journal
DOI：https://doi.org/10.1016/S0009-2614(02)01963-2
DOI ID：10.1016/S0009-2614(02)01963-2, ISSN：0009-2614, SCOPUS ID：0037422855, Web of Science ID：WOS:000180795200007 - Diffusion-model analysis of effective CIDEP distance in solvent-separated radical-ion pair
Y Kobori; T Yago; S Tero-Kubota
APPLIED MAGNETIC RESONANCE, Volume：23, Number：3-4, First page：269, Last page：287, 2003, [Reviewed]
The radical pair mechanism (RPM) of chemically induced dynamic electron polarization (CIDEP) is theoretically analyzed to determine what intermolecular separations (r(eff)) effectively contribute to the CIDEP generated from diffusive, separated radical-ion pairs (RIP) in terms of the charge-transfer interaction in the singlet-triplet energy splitting (J) by taking into account the distance-dependent electronic coupling and reorganization energy. The diffusion-model analysis reveals that the hyperfine-dependent RPM polarization (P-RPM) phase is varied with the driving force (-DeltaG(CR)) for the charge-recombination (CR) process and that the boundary -DeltaG(CR) between the opposite phases coincides well with the total reorganization energy around the diffusible separation distance, r(eff) = 1.2 nm, between the ion radicals. For the first time, the r(eff) is well described by the exponent parameter 66) in the distance-dependent electronic coupling, suggesting that the RPM CIDEP detection can be applied to characterize the electronic coupling in individual solvent-separated RIP systems. It has been concluded that, in contrast to the spin exchange interaction of the neutral radical pairs, the characteristic long-range charge-transfer interaction enables us to utilize the simple diffusion-model analysis to successfully evaluate the r(eff) and the P-RPM, in homogeneous liquid polar solvents.
SPRINGER WIEN, English, Scientific journal
DOI：https://doi.org/10.1007/BF03166621
DOI ID：10.1007/BF03166621, ISSN：0937-9347, eISSN：1613-7507, SCOPUS ID：0037266438, Web of Science ID：WOS:000182097000003 - Time-resolved EPR study on reorganization energies for charge recombination processes in nanometer-separated radical ion pairs
T Yago; Y Kobori; K Akiyama; S Tero-Kubota
JOURNAL OF PHYSICAL CHEMISTRY B, Volume：106, Number：39, First page：10074, Last page：10081, Oct. 2002, [Reviewed]
The reorganization energies for the intermolecular charge recombination processes have been determined for the electron donor-acceptor systems involving the quinones and methoxy aromatic molecules by time-resolved EPR and cyclic voltammetry measurements in polar solvents. We have carefully examined what distance between the donor and acceptor molecules is effective for the radical pair mechanism (RPM) chemically induced dynamic electron polarization (CIDEP) detection using the stochastic Liouville equation on the basis of the charge transfer (CT) interaction mechanism in the singlet-triplet energy splitting (2J) in radical ion pairs. The RPM CIDEP shows that the signs of the J are inverted from positive to negative with decreasing temperature. The results are interpreted by the CT interaction mechanism, With the observations of the J 0 condition, the individual values of the total and solvent reorganization energies (As) are determined for several 1.2 nm separated donor-acceptor systems. ne individual As values ranging from 1.27 to 1.39 eV in the present donor-acceptor systems agree with those calculated from the Marcus continuum dielectric model at 1.2 nm donor-acceptor separation within the deviation of similar to0.1 eV. In the dimethoxynaphthalene (DMN)duroquinone (DQ) system, the solvent reorganization around the methoxy groups is dominated due to the localization of the electron spin density in the DMN cation radical.
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/jp021119s
DOI ID：10.1021/jp021119s, ISSN：1520-6106, Web of Science ID：WOS:000178273500014 - Determination of electron-transfer reorganization energy in nanometer-separated radical ion pair by time-resolved EPR spectroscopy
Y Kobori; T Yago; K Akiyama; S Tero-Kubota
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Volume：123, Number：39, First page：9722, Last page：9723, Oct. 2001, [Reviewed]
AMER CHEMICAL SOC, English, Scientific journal
DOI：https://doi.org/10.1021/ja015752n
DOI ID：10.1021/ja015752n, ISSN：0002-7863, PubMed ID：11572713, SCOPUS ID：0035802367, Web of Science ID：WOS:000171407800045
■ Research projects
- マイクロ波とラジオ波を用いたスピン化学の手法による選択的同位体濃縮
30 Jul. 2020 - 31 Mar. 2024
Grant amount(Total)：25740000, Direct funding：19800000, Indirect funding：5940000
Grant number：20K20557 - ナノ構造体での励起子分裂および励起子融合の機構解明とその制御
01 Apr. 2020 - 31 Mar. 2023
Grant amount(Total)：4420000, Direct funding：3400000, Indirect funding：1020000
Grant number：20K05416 - スピン化学の手法を用いた励起子融合の詳細なメカニズム解明および新規材料開発
01 Apr. 2019 - 31 Mar. 2022
Grant amount(Total)：17680000, Direct funding：13600000, Indirect funding：4080000
Grant number：19H02670 - Universal and Specific Features of Geminate Delayed Fluorescence by Triplet Fusion
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), 01 Apr. 2019 - 31 Mar. 2022
Seki Kazuhiko, National Institute of Advanced Industrial Science and Technology
Grant amount(Total)：4420000, Direct funding：3400000, Indirect funding：1020000
Singlet fission (SF) is a photochemical process, which generates two triplets from a singlet exciton. Its reverse process is termed triplet fusion (TF). When TF occurs between the same geminate triplet-pair generated by SF, delayed fluorescence by geminate fusion might occur when TF between geminate pair involves diffusional encounter. The delayed fluorescence after pulsed excitation decays by power law. In 1,2, and 3 dimensions, the exponent is -3/2, -1 (apart from logarithmic dependence), and -3/2, respectively. The exponent of the power law decay reflects the diffusional anisotropy. Theoretically, the exponent of the power law decay may change from -1 of 2 dimensions to -3/2 of 3 dimensions as time proceed for certain values of the anisotropy ratio in the triplet diffusion constants but the diffusion should be highly anisotropic (1000 times different) to obtain such cross-over. The theoretical results are compared to the measured fluorescence decay in tetracene and rubrene.
Grant number：19K05395 - Structural Analysis on Short-Lived Triplet Pairs Generated by Singlet Fission
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), 01 Apr. 2017 - 31 Mar. 2021
Yago Tomoaki, Saitama University
Grant amount(Total)：4940000, Direct funding：3800000, Indirect funding：1140000
Triplet pairs are generated by singlet fission in organic solids. Triple pairs are important intermediate to determine the efficiency of singlet fission. However nature of the triplet pair states has not been clarified due to the short lifetime of triplet pairs. The magnetic field effects on delayed fluorescence are often observed after singlet fission and triplet fusion. We have measured magnetic field dependence of the intensity of delayed fluorescence with several organic crystals. We determined the structure of a triplet pair generated by singlet fission. The structure of triplet pair for efficient singlet fission were discussed on the basis of the magnetic field dependence of the delayed fluorescence.
Grant number：17K05742 - Study of Magnetic Field Effects on Singlet Fission
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), 01 Apr. 2016 - 31 Mar. 2019
WAKASA Masanobu, Saitama University
Grant amount(Total)：17420000, Direct funding：13400000, Indirect funding：4020000
Magnetic field effects (MFEs) on triplet pair generated by singlet fission (SF) in an organic crystal, 1,6-diphenyl-1,3,5-hexatriene, were studied by steady-state fluorescence measurements under ultra-high magnetic fields of up to 30 T and by time-resolved fluorescence measurements with sub-nanosecond time resolution. The observed MFEs were analyzed by using stochastic Liouville equation based on the radical pair (RP) model. The excellent agreements between the observed and simulated MFEs demonstrate that the RP model can apply to the analysis of the MFE on triplet pair with a modification of the spin Hamiltonian.
Grant number：16H04093 - Development of a new spin probe method using the visible laser pulse
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Young Scientists (B), 01 Apr. 2013 - 31 Mar. 2015
YAGO Tomoaki, Saitama University
Grant amount(Total)：4160000, Direct funding：3200000, Indirect funding：960000
Time-resolved Faraday rotation measurements were performed using photo-excited state of organic molecules. In ionic liquids, the spin system where the two unpaired electron spins are strongly correlated were observed by using the nano-second laser flash photolysis with the combination of the magnetic field. By the application of Miller-Guy method, the analysis of the stochastic Liouville equations was modified to calculate the time evolution of the complex spin system. Electron spin resonance measurements could not be performed due to the trouble of the spectrometer.
Grant number：25870123 - Reaction Dynamics in Nano-space as Studied by Time-resolved
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), 2010 - 2012
WAKASA Masanobu; YAGO Tomoaki, Saitama University
Grant amount(Total)：20410000, Direct funding：15700000, Indirect funding：4710000
560 GHz time-resolved high-frequency ESR was developed by using30 tesla pulsed magnet and THz light source. Moreover,inhomogeneous nano-space was studied by the magnetic field effect (MFE) probe. In mesoporous silica MCM-41, increases of micro-viscosity were observed by formation of partially clusterization of solvent. In the case of ionic liquids, inhomogeneous structure, which lifetimes were 20-120 ns,was generated in spite of a liquid.
Grant number：22350003 - Construction of time-resolved Faraday rotation measurement system and its application to the organic spin polarized materials.
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Young Scientists (B), 2009 - 2010
YAGO Tomoaki, Saitama University
Grant amount(Total)：4420000, Direct funding：3400000, Indirect funding：1020000
The purpose of the present study is generation and detection of the large magnetization in organic materials by employing the photo-excited triplet states of organic molecule. Time-resolved Faraday rotation measurement system has been developed by using the lasers, polarizers, and amplifiers. Also the magnetic resonance study on the photo-excited triplet state was performed in Prof. Lin's laboratory at Washington University in St. Louis, collaborating with Prof. Lin and Prof. Kothe from Freiburg University in Germany. Theoretical analysis revealed that the large spin polarizations are generated in the level-crossing region of the triplet state.
Grant number：21750009 - Development of pico-second spin detection instrument using the photo-excited triplet state
Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Young Scientists (Start-up), 2007 - 2008
YAGO Tomoaki, Saitama University
Grant amount(Total)：3034000, Direct funding：2650000, Indirect funding：384000
Grant number：19850004 - -
Competitive research funding - -
Competitive research funding