DOI： 10.1038/s41467-023-40557-7

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.202302714

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/ejic.202300125

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The use of molecular spins as quantum bits is fascinating because it offers a wide range of strategies through chemical modifications. In this regard, it is very interesting to search for organic radical ions that have small spin-orbit coupling values. On the other hand, the feature of the magnetic relaxation of π-organic radical ions is rarely exploited due to the difficulty of spin dilution, and π-stacking interaction. In this study, we focus on N,N′,N′′-tris(2,6-dimethylphenyl)benzenetriimide (BTI-xy), where three xylene moieties connected to the imide groups cover the π-plane of the BTI core. As a result, BTI-xy radical anions without π-stacking interaction were obtained. This led to the slow magnetization relaxation, which is reported for the first time in organic radicals. Furthermore, the relaxation times in a solution state revealed the importance of spin interaction.

DOI： 10.1039/d2cp06026d

PubMed

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1007/s00723-022-01519-2

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1007/s00723-022-01520-9

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1007/s00723-022-01519-2

Repository URL： http://hdl.handle.net/10466/0002000444

Publishing type：Research paper (scientific journal)  

We present methods for optimizing frequency sweeps for “fast” adiabatic inversion in ESR spectroscopy. To perform the sought optimization, we need to either exploit “constant adiabaticity” chirps or utilize the gradient ascent pulse engineering (GRAPE) method: in these ways, the Δ(t) profiles are evaluated, which allow one to minimize the duration of the chirps. Arbitrary waveform generator-based ESR (AWG-ESR) enables us to apply versatile MW-shaped pulses and to control dynamics of the spin systems under study. Spin dynamics for spin inversion by the shaped pulses were observed. Comparison of different frequency sweeps applied to both a homogeneous ESR signal and a spin packet of inhomogeneously broadened ESR signals indicates that the duration of the adiabatic sweeps can be significantly reduced.

DOI： 10.1007/s00723-022-01513-8

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/ajoc.202300224

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1021/acs.jpclett.2c02737

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

DOI： 10.1038/s42004-022-00701-8

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/chem.202201426

PubMed

Publishing type：Research paper (scientific journal)  

<p>We designed and synthesized a triphenylphenylnitroxide–(nitronyl nitroxide) dyad with a structure isoelectronic with trimethylenemethane. Crystal structure analysis demonstrated that the dihedral angle between the nitroxide and nitronyl nitroxide moieties was excessively small due to the steric effects of the triphenylphenyl moiety. The coplanarity of the two radical systems induced an excessively strong ferromagnetic intramolecular interaction (2<i>J</i>/<i>k</i>_B ≥ +2000 K; <i>H</i> = −2<i>J</i><b>S_1/2</b>•<b>S_1/2</b>).</p>

DOI： 10.1246/cl.220021

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jacs.2c00476

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/chem.202104447

PubMed

Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/chem.202104447

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.inorgchem.1c03764

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Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.202205729

PubMed

Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/anie.202205729

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.inorgchem.1c02806

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Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jacs.1c10151

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpclett.1c03214

PubMed

Publishing type：Research paper (scientific journal)  

Bayesian phase difference estimation (BPDE) is a controlled-time evolution-free quantum algorithm that is capable of computing the energy difference between two electronic states directly, without inspecting the total energies of individual states.

DOI： 10.1039/d1cp03156b

PubMed

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The structural dynamics of the chromo-shadow domain (CSD) and chromodomain (CD) of human HP1 proteins essential for heterochromatin formation were investigated at the nanosecond and nanometer scales by site-directed spin labeling electron paramagnetic resonance and pulsed double resonance spectroscopy. Distance measurements showed that the spin-labeled CSD of human HP1α and HP1γ tightly dimerizes. Unlike CD-CD interaction observed in fission yeast HP1 in an inactivated state (Canzio et al., 2013), the two CDs of HP1α and HP1γ were spatially separated from each other, dynamically mobile, and ready for a Brownian search for H3K9-tri-methyl(me3) on histones. Complex formation of the CD with H3K9me3 slowed dynamics of the domain due to a decreased diffusion constant. CSD mobility was significantly (∼1.3-fold) lower in full-length HP1α than in HP1γ, suggesting that the immobilized conformation of human HP1α shows an auto-inactivated state. Differential properties of HP1α and HP1γ to form the inactive conformation could be relevant to its physiological role in the heterochromatin formation in a cell.

DOI： 10.1016/j.bbrc.2021.06.010

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.joc.1c00880

PubMed

Publishing type：Research paper (scientific journal)  

Multinuclear AuI complexes with two or three nitronyl nitroxide-2-ide radical anion and phosphine-ligand scaffolds, (NN-Au)2-1 o, (NN-Au)2-1 m, and (NN-Au)2-1 p, have been synthesized to investigate the influence of AuI−AuI (aurophilic) interactions on the properties of multispin molecular systems. The desired complexes were successfully prepared in moderate yields in a one-pot synthesis from the corresponding phosphine ligand, AuI source, parent NN, and sodium hydroxide. Among the prepared complexes, (NN-Au)2-1 o, in which an aurophilic interaction was clearly observed by crystal structure analysis, showed characteristic spin−spin interactions, electrochemical properties, and solvatochromic behavior. The results from theoretical calculations also suggested that the differences in properties between complex (NN-Au)2-1 o and the other complexes are due to intramolecular aurophilic interactions.

DOI： 10.1002/chem.202101483

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Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/chem.202101483

Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s00723-021-01392-5

Publishing type：Research paper (scientific journal)  

The readout in the dispersive regime is originally developed—and it is now largely exploited—for non-demolitive measurement of super- and semiconducting qubits. More recently it has been successfully applied to probe collective spin excitations in ferro(i)magnetic bulk samples or collections of paramagnetic spin centers embedded into microwave cavities. The use of this readout technique within a semiclassical limit of excitation is only marginally investigated although it holds for a wide class of problems, including advanced magnetic resonance techniques. In this work, the coupling between a coplanar microwave resonator and diphenyl-nitroxide organic radical diluted in a fully deuterated benzophenone single crystal is investigated. Two-tone transmission spectroscopy experiments demonstrate the possibility to reconstruct the spectrum of the spin system with little loss of sensitivity with respect to the resonant regime. Likewise, pulse sequences of detuned microwave frequency allow the measurement of the spin-lattice relaxation time (T1). The independent tunability of the probe and the drive power enables one to adjust the signal-to-noise ratio of the spectroscopy. These results suggest that electron spin dispersive spectroscopy can be used as a complementary tool of electron spin resonance to investigate the spin response.

DOI： 10.1002/qute.202100039

Publishing type：Research paper (scientific journal)  

<p>A [2 × 2] cobalt grid complex containing a ditopic arylazo trianion-radical ligand is shown to exhibit valence tautomerism in the solid state.</p>

DOI： 10.1039/d1cc01991k

PubMed

Publishing type：Research paper (scientific journal)  

<p>In this study, we analyzed the different parts of mushrooms using electron spin resonance (ESR) to identify radical species, and we examined their hydroxyl radical scavenging activities. The four kinds of mushrooms investigated in this study, <i>Agrocybe cylindracea</i> (Shakkiko1 and Shakkiko2), <i>Grifola gargal</i>, and <i>Coprinus comatus</i> were separated into caps, stipes, and bases of stipes. ESR spectra of all specimens consisted of signals originating from organic free radicals, Fe³⁺, Mn²⁺, and Cu²⁺ species. The cap showed the highest Fe content. The different mushroom body parts revealed different hydroxyl radical scavenging activity values, among which the <i>C. comatus</i> stipes were the highest. The radical scavenging activities of the evaluated specimens did not correlate with the Fe contents; however, a positive correlation with the Cu contents was observed.</p>

DOI： 10.3136/fstr.27.529

CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.3390/magnetochemistry7050071

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpclett.1c00283

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Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d0sc04847j

PubMed

Publishing type：Research paper (scientific journal)  

A nitronyl nitroxide unit (NN) was linked with a triphenylamine-based condensed polycyclic skeleton DOTT to form a radical substituted donor NN-DOTT. X-ray crystal structure analysis demonstrated a flat bowl shape of the DOTT unit. EPR spectra showed the localization of electron spin on the NN unit. Chemical oxidation of the DOTT unit produced radical-substituted radical cation salts NN-DOTT+ . SbF6- and NN-DOTT+ . FeBr4- that are stable under ambient conditions. The magnetic behavior of NN-DOTT+ . SbF6- is characterized by the strong intramolecular ferromagnetic interaction between NN and DOTT+. The X-ray structural analysis of NN-DOTT+ . FeBr4- shows planar structure of DOTT and 1D mixed-stack column of NN-DOTT+ and FeBr4-. Magnetic measurements established that NN-DOTT+ . FeBr4- undergoes magnetic phase transition into a weak ferromagnet at 7 K.

DOI： 10.1002/asia.202001227

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Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/asia.202001227

Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d0cp03745a

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Publishing type：Research paper (scientific journal)  

DOI： 10.1002/slct.202002927

Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/slct.202002927

J-GLOBAL

Publishing type：Research paper (scientific journal)  

A series of stable and genuinely organic open-shell systems, 7r-conjugated plienoxyl nitro)ride free radicals (hybrid phenoJql riitroxide radicals), have been synthesized and their magnetic properties in the crystalline state investigated, revealing their usefulness as new building blocks for molecular magnetic materials. The salient electronic structure of the hybrid phenoxyl nitroxide radicals is extended Tr-spin delocalization from the nitroxide moiety, mediating the localization effect intrinsic to nitroxide radicals. Five representative hybrid radicals containing an aliphatic, aromatic, and heteroaromatic substituent inthe sidepart wof the compact hybrid radical centers ere synthesized, andtheir lectflar/crYstal structures in theccwrYstall_ine state. were determine X-raY diffraction analyses..sPYectroscoPY). and D rXthbeanhclYbErid radicals.confirmedd. that an unpaired spin delocalizes over, the whole molecular FT calculations for; SR 1H-ENDOR frame including the.nollconiugate.d fragments, suggestingthe possibility of tuning their electronic properties throughsubstituefft effects in the crystalline state. Significant influence of the phenoxylmoiety on the electronic, structure was analyzedin terms of the gtensor calculations. The_.SQUID magffetizatiori measurements revealed that(AFM) (CJ hearing alkyl or aromatic substituefft: behave as 3D Curie Weiss paramagnets. with weak antiferromagne 1 to 2.6 K) or ferromagnetic (FM) ( +0.33 K) spin-spin exchange interactions. On the other hand, heteroaro tically substituted hybrid phenoxyl nitroxide showedsignificant AFM interactions with J/k1 7-25-6 K. The analysis;of the bulk amagnetic Pr Perties based on. the.crYstall graPhic data and DFT calculations revealed competition between the intermolecular. AFM and FM interactions which originate fromthdeirnCer s (l/henofql)"'"Me(flitr.ofti'de) (N)O C. (arom.) infinite ID head -to -tail chains and the C(arom) Carom) head-over-tail forming'; 3D networks in their crystal lattices.

DOI： 10.1021/acs.jpca.9b11856

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/chem.201905465

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Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/chem.201905465

Publishing type：Research paper (scientific journal)  

<p>Two 4,8,12-trioxotriangulene neutral radical derivatives having isopropyl and <i>n</i>-butyl groups were newly synthesized using different methods, and their electronic-spin structures were elucidated. In solution state, both neutral radicals formed diamagnetic π-dimers stabilized by strong multiple SOMO-SOMO interaction. The solid-state electronic spectra suggested that the steric effect of the alkyl groups had a significant effect on the π-stacking structure, causing different intermolecular absorption bands at the near-infrared region.</p>

DOI： 10.1246/cl.190761

CiNii Article

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Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c9qo00663j

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DOI： 10.1021/acs.jpca.9b07169

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c8dt02150c

Publishing type：Research paper (scientific journal)  

Three new mixed triradicals with small exchange coupling parameters (J << A(N)) were obtained on the base of a coupling reaction between the derivative of spirofused 2,5-dihydroimidazol-type monoradical and the two mol. equivalents of carboxylic acid derivatives of PROXYL-, TEMPO- or 2,5-dihydro-1H-pyrrol-type nitroxides. Their intramolecular magnetic interactions were characterized in terms of comparison of the CW X, Q- and W-band EPR spectra with those of the monoradical precursors. The dipole-dipole coupling parameters of the triradicals were estimated on the base of the quantum chemical calculations at UB3LYP/6-31G(d) level of theory. Two types of the spin distances were found in the triradicals: short-with the distance of 13-17 angstrom (D approximate to 11-24MHz) and long-with the distance of 21-23 angstrom (D approximate to 4-6MHz). The longest spin-spin as well as spin-lattice relaxation times at 50K were detected for the triradical carrying the two TEMPO fragments, indicating the potential usage of three-spin qubit models for quantum gate operations.

DOI： 10.1007/s00723-019-01125-9

Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c9cp02546d

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Publishing type：Research paper (scientific journal)  

JACS spotlight selected. DOI: 10.1021/jacs.9b06488<br />
<br />
Synfacts selected (https://www.thieme-connect.de/products/ejournals/html/10.1055/s-0039-1689812)<br />
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DOI： 10.1021/jacs.9b04080

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DOI： 10.1002/cplu.201800662

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Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/cplu.201800662

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DOI： 10.1002/chem.201900513

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DOI： 10.1002/asia.201801615

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DOI： 10.1021/acscentsci.8b00788

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DOI： 10.1021/acsami.8b14967

Publishing type：Research paper (scientific journal)  

© The Royal Society of Chemistry. The fictitious spin-1/2 (effective spin-1/2) Hamiltonian approach has been the putative method to analyze the conventional fine-structure/hyperfine ESR spectra of high spin metallocomplexes with sizable zero-field splitting (ZFS) tensors since the early 1950s, and the approach gives salient principal geff-values far from g = 2 without explicitly affording their ZFS values in most cases. The experimental geff-values thus determined, however, never agree with those (gtrue-values) of the true principal g-tensors, which are obtainable from reliable quantum chemical calculations. We have recently derived exact or extremely accurate analytical expressions for the geff/gtrue relationships for the spin quantum number S's up to S = 7/2 (T. Yamane et al., Phys. Chem. Chem. Phys., 2017, 19, 24769-24791). In this work, we have removed the limitation of the collinearity between g- and ZFS tensors and derived the generalized geff/gtrue relationships. To illustrate the usefulness of the present approach, we have revisited important typical high spin systems with large ZFS values such as picket fence metalloporphyrins with MnII (S = 5/2) (Q. Yu et al., Dalton Trans., 2015, 44, 9382-9390), a 6th ligand coordinated porphyrin with FeIII (S = 5/2) (Y. Ide et al., Dalton Trans., 2017, 46, 242-249) and a pseudo-octahedral CoII (S = 3/2)(hfac)2 complex (D. V. Korchagin et al., Dalton Trans., 2017, 46, 7540-7548), completing the ESR spectral and magnetic susceptibility analyses and gaining significant physical insights into their electronic structures. The off-principal axis extra peaks overlooked in the documented spectra of the picket fence MnII porphyrins have fully been assigned, affording their accurate true g-, hyperfine and ZFS tensors, for the first time. For the CoII complex, the occurrence of the non-collinearity between the g- and ZFS tensors has been discussed by using the generalized geff/gtrue relationships. We have attempted to carry out reliable DFT-based and ab initio quantum chemical calculations of their magnetic tensors, in which spin-orbit couplings are incorporated, reproducing the experimental true tensors. We emphasize that the incorporation of multi-reference nature in the electron configuration is important to interpret the magnetic tensors for the CoII complex.

DOI： 10.1039/c8dt02988a

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Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.cpletx.2018.100002

Publishing type：Research paper (scientific journal)  

© 2018 Elsevier Ltd Fe-transferrins/their homologues in ex-vivo mushrooms were identified by ESR spectroscopy at liquid helium temperature, 4 K. The ESR fine-structure signals from Grifola frondosa were analyzed by spectral simulation with a full spin-Hamiltonian approach, determining the spin Hamiltonian parameters of the ferric iron species bound in the biological environment: S = 5/2, g = (2.045, 2.01, 2.235), |D| = 0.28 cm−1, |E/D| = 0.05. The zero-field splitting (ZFS) parameters, D- and E-values, are very close to the reported values, |D| = 0.25 cm−1and |E/D| = 0.06, for an Fe-transferrin with oxalate anion, and to |D| = 0.25 cm−1and |E/D| = 0.04 for one with malonate anion in human sera, suggesting that the Fe3+species are from Fe-transferrins or their homologues. Quantum chemical calculations of the ZFS tensors for Fe-transferrins were carried out. Fe-transferrins/homologues have been identified for all the mushrooms under study, suggesting that such Fe3+enzymes are widely distributed in mushrooms.

DOI： 10.1016/j.foodchem.2018.05.092

Publishing type：Research paper (scientific journal)  

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Reversible solution π-dimerization is observed in the stable neutral phenoxyl radical 2,6-bis-(8-quinolylamino)-4-(tert-butyl)phenoxyl baqp and is spectroscopically characterized. This behavior, not previously observed for π-extended phenoxyl radicals, is relevant to the formation of long multicenter bonding in the π-dimer at low temperature akin to previously reported phenalenyl radicals. Our experimental data are supported in a quantitative manner by results from density functional theory (DFT) and ab initio molecular orbital theory calculations. Our theoretical results indicate that the solution dimer features strong bonding interactions between the two phenoxyl rings but that the stability of the dimer is also related to dispersion interactions between the flanking nearly parallel quinolyl rings.

DOI： 10.1002/chem.201802204

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Publishing type：Research paper (scientific journal)  

© 2018 The Chemical Society of Japan. To stabilize organic neutral radicals, which are usually very unstable chemical species in air atmosphere, "steric protection" is the most general and indispensable method. Based on the design of electronic-spin structure of polycyclic carboncentered π-radicals, we have for the first time realized a peculiarly stable neutral π-radical without bulky substituent groups, 4,8,12-trioxotriangulene (TOT), whose decomposition point is higher than 240 °C in the solid state under air. This remarkably high air-stability as a neutral radical is achieved by spin-delocalization originating from the symmetric and expanded π-electronic structure of TOT. The oxo-functionalities also highly contribute to the high stability through electronicspin modulation, where the largest electronic spin density located at the central carbon atom further decreases the spin densities of the peripheral carbon atoms. In the solution state, TOT is in the equilibrium between the monomer and highly symmetric π-dimer, as stabilized by the formation of the strong two-electron-multicenter bonding. Crystal structure analysis revealed that TOT derivatives show strong self-assembling ability forming one-dimensional columns, which further construct three-dimensional networks by multiple intercolumnar non-covalent interactions due to the absence of bulky substituent groups. Substituent groups at the apexes of the triangular carbon-framework of TOT afford variations of the π-stacking mode in the one-dimensional columns, influencing the magnetic properties and photo-absorptions around the near-infrared region. The electronic effect of the substituent groups also affects the redox potentials of TOT. The peculiarly high stability of TOT neutral radicals and their three-dimensional networks by robust intermolecular interactions achieved in our study are very beneficial for the molecular design of new polycyclic air-stable neutral radicals. Furthermore, we believe that the open-shell electronic structures of neutral π-radicals, which are quite different from those of close-shell molecular systems, will also produce milestones for the exploration of peculiar physical properties and catalytic activity for organic transformation originating from their unconventional electronic-spin nature.

DOI： 10.1246/bcsj.20180074

CiNii Article

Publishing type：Research paper (scientific journal)  

A method is proposed for optimizing the performance of the APSOC (Adiabatic-Passage Spin Order Conversion) technique, which can be exploited in NMR experiments with singlet spin states. In this technique magnetization-to-singlet conversion (and singlet-to-magnetization conversion) is performed by using adiabatically ramped RF-fields. Optimization utilizes the GRAPE (Gradient Ascent Pulse Engineering) approach, in which for a fixed search area we assume monotonicity to the envelope of the RF-field. Such an approach allows one to achieve much better performance for APSOC
consequently, the efficiency of magnetization-to-singlet conversion is greatly improved as compared to simple model RF-ramps, e.g., linear ramps. We also demonstrate that the optimization method is reasonably robust to possible inaccuracies in determining NMR parameters of the spin system under study and also in setting the RF-field parameters. The present approach can be exploited in other NMR and EPR applications using adiabatic switching of spin Hamiltonians.

DOI： 10.1016/j.jmr.2018.03.005

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

© 2018 American Chemical Society. Möbius aromatic molecules have attracted great attention as new functional materials because of their π-orbital cyclic conjugations lying along the twisted Möbius topology. To elucidate the electronic character of the lowest excited triplet (T1) state of a Möbius aromatic [28]hexaphyrin, we employed a time-resolved electron paramagnetic resonance (TREPR) method with applied magnetophotoselection measurements at 77 K. Analyses of the EPR parameters have revealed that the T1state possesses intramolecular charge-transfer (CT) character together with local excitation character residing at one side in the Möbius strip ring. We have also demonstrated that the CT character between orthogonal unpaired orbitals triggers quick triplet deactivation by spin-orbit coupling. This deactivation can be an important barometer to represent the "antiaromaticity" because of a connection between the orthogonal CT character and instability by a weakened spin-spin exchange coupling in the T1state.

DOI： 10.1021/acs.jpclett.8b00740

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DOI： 10.1039/c7cp05533a

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DOI： 10.1002/asia.201701085

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DOI： 10.1002/chem.201703220

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DOI： 10.1021/jacs.7b05709

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DOI： 10.1039/c7cp03850j

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DOI： 10.1021/acs.joc.6b02500

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DOI： 10.1515/zpch-2016-0799

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DOI： 10.1021/acs.jpca.6b10253

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DOI： 10.1002/anie.201604320

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DOI： 10.1021/acs.jpca.6b04932

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DOI： 10.1007/s11128-015-1142-6

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DOI： 10.1007/s11128-015-0985-1

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DOI： 10.1039/c4cp04744c

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DOI： 10.1039/C4CP04744C

Other URL： http://orcid.org/0000-0003-1274-7470

DOI： 10.5111/bunkou.64.1_289

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DOI： 10.1002/ejic.201402564

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DOI： 10.1021/ja504774q

Publishing type：Research paper (scientific journal)  

We have designed and synthesized chiral molecules with nitronyl nitroxide (NN) radicals directly bound to the chiral centers, (<i>S</i>)-1,3-dioxolane-4-NN (<b>1</b>) and (<i>R</i>)-oxazolidine-4-NN (<b>2</b>). These radicals were synthesized from <small>D</small>-mannitol in four steps for <b>1</b> and from <small>L</small>-serine in six steps for <b>2</b> in moderate yields. They were characterized by means of mass spectrometry, electron spin resonance, elemental analyses, and X-ray crystal structure analyses. Their magnetic properties were also investigated using a SQUID magnetometer. The temperature dependence of paramagnetic susceptibility (χ_p) indicates the presence of a weak antiferromagnetic intermolecular interaction with <i>J</i>/<i>k</i>_B = −3.1 K and <i>θ</i> = −5.5 K for <b>1</b>, and a weak ferromagnetic intermolecular interaction with <i>J</i>/<i>k</i>_B = +0.5 K for <b>2</b>. We also succeeded in preparing the metal complex [Mn(hfac)₂(<b>2</b>)]₂–[Cu(hfac)₂], which was characterized by a strong antiferromagnetic interaction (<i>J</i>/<i>k</i>_B = −140 K) between [Mn(hfac)₂] and <b>2</b> along with a much weaker antiferromagnetic interaction (<i>J</i>/<i>k</i>_B = −0.11 K) between the [Mn(hfac)₂(<b>2</b>)] unit and [Cu(hfac)₂].

DOI： 10.1246/bcsj.20130264

CiNii Article

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DOI： 10.1021/ic4020898

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DOI： 10.1039/c4cp00822g

Publishing type：Research paper (scientific journal)  

Weakly exchange-coupled biradicals have attracted much attention in terms of their dynamic nuclear polarisation application in NMR spectroscopy for biological systems or the use of synthetic electron-spin qubits in quantum information processing/quantum-computing technology. Analogues multi-partite molecular systems are important in entering a new phase of the relevant fields. Many stable organic biradicals known so far have nitrogen nuclei at their electron spin sites, where singly occupied molecular orbitals are dominating and large hyperfine couplings occur. A salient feature of such weakly exchange-coupled molecular systems in terms of electronic spin structures is underlain by small zero-field splitting (ZFS) parameters comparable with nuclear hyperfine and/or exchange interactions. Pulse-based electron spin nutation (ESN) spectroscopy of weakly exchange-coupled biradicals, applicable to oriented or non-oriented media, has proven to be a useful and facile approach to the determination of ZFS parameters, which reflect relatively short distances between unpaired electron spins. In the present study, we first treat two-dimensional single-crystal ESN spectroscopy (Q-band) of a N-15-labelled weakly exchange-coupled biradical, showing the nuclear hyperfine effects on the ESN phenomena from both the experimental and theoretical side. ESN spectroscopy is transition moment spectroscopy, in which the nutation frequency as a function of the microwave irradiation strength (1) (angular frequency) for any cases of weakly exchange-coupled systems can be treated. The results provide a testing ground for the simplified but general approach to the ESN analysis. In this study, we have invoked single-crystal electron-electron double resonance measurements on a typical biradical well incorporated in a diamagnetic host lattice and checked the accuracy of our ESN analysis for the spin dipolar tensor and exchange interaction. Next, we extend the general approach to analogues multi-partite molecular systems such as stable organic triradical, in which the exchange interaction can be governed by a significant amount of the delocalisation of three unpaired spins over the molecular frame of a triangular structure. The triangular structure maintains -conjugation in which each spin-bearing nitroxide at the vertex participates and the exchange interaction is greatly controlled by the dihedral angle between the -conjugation plane and nitroxide moiety at the vertex. In this context, the ZFS parameters do not correspond to spin distances (1.0nm) in a straightforward manner, but reflect a salient electronic structure associated with both the -electron network and the symmetry property of the triradical under study. Thus, both the D-value and exchange interaction J have been controlled in this study. In order to interpret the experimental ZFS parameters and exchange interaction, which is three-order of magnitude reduced in the present poly(methyl methacrylate) polymer matrix compared with that in the crystal, sophisticated quantum chemical calculations of the ZFS tensor and exchange interaction were carried out and reproduced the experimental values, concluding that the present triradical of the triangular structure undergoes significant twisting at the nitroxide sites in the polymer matrix. In this study, we observed electron spin resonance forbidden transitions between the Ms-manifolds belonging to the spin-doublet ground state and spin-quartet excited state. The observation enables us to derive the magnitude of the exchange coupling.

DOI： 10.1080/00268976.2013.811304

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/chem.201301783

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/asia.201300471

Publishing type：Research paper (scientific journal)  

By binding of a ligand molecule carrying an electron spin to a guanine-guanine mismatch in a DNA duplex on a DNA tile, a three-dimensional assembly of electron spins was successfully constructed.

DOI： 10.1039/c3cc41801d

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.201302091

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.201301435

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/chem.201203755

Publishing type：Research paper (scientific journal)  

The lowest excited triplet (T-1) pi pi* states of gallium (Ga) and various rhodium (Rh) 5,10,15-trispenta-fluorophenyl corroles (Cors) were studied in the liquid crystal (LC) E-7 and in rigid glasses by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. The triplet sublevel energies were experimentally determined by the alignment of the molecules in the LC and by magneto-photoselection in the glass. The sublevel scheme of GaCor was determined by calculating the zero field splitting (ZFS) parameters. Axial ligand effects and quantum chemical calculations were used for the sublevel assignment of RhCors. The anisotropic EPR parameters were used to determine the important higher excited states and the magnitudes of their spin-orbit coupling (SOC) contributions were evaluated. On the basis of these results and analyses, the EPR parameters and triplet lifetime were discussed for each RhCor complex.

DOI： 10.1021/jp3071037

Publishing type：Research paper (scientific journal)  

The synthesis and the solid state magnetic properties of (nitronyl nitroxide)-substituted trioxytriphenylamine radical cation tetrachlorogallate, NNTOT+center dot GaCl4-, are reported. In the temperature region between 300 and 3 K, the magnetic behavior is characterized by the strong intramolecular ferromagnetic interaction (J/kB=+400 K) between the radical (NN) and the radical cation (TOT+) and the weak intermolecular antiferromagnetic interaction (J/kB=-1.9 K) between NNTOT+ ions. Below 3 K, a 3D-type long-range magnetic ordering into a weak ferromagnet was observed (TN=2.65 K). The magnetic entropy (Smag=8.97 J?K-1?mol-1) obtained by the heat capacity measurement is in good agreement with the theoretical value of R?ln3=9.13 J?K-1?mol-1 based on the S=1 state.

DOI： 10.1002/asia.201200084

Publishing type：Research paper (scientific journal)  

An ESR hyperfine splitting pattern of a biradical in solution depends on the magnitude of the intramolecular exchange interaction J(intra) compared with the hyperfine coupling constant A. Some biradicals exhibit their hyperfine splitting patterns characteristic of a monoradical, even though their exchange interaction is strong enough, vertical bar J(intra)vertical bar &gt;&gt; vertical bar A vertical bar. The contradiction in ESR spectroscopy is known as "biradical paradox", puzzling scientists for a long time. In this study, it is shown from ESR spectral simulations underlain by a theoretical model of a series of spin Hamiltonians that noncovalent aggregation of biradical molecules in solution leads to the appearance of paradoxical ESR spectra. Most of the spins in an aggregate of one dimension lose their contribution to the ESR spectra owing to intermolecular antiferromagnetic interactions J(inter), leaving two outermost spins ESR-active in the aggregate of one dimension. Paradoxical ESR spectra appear only when J(intra) and J(inter) fall within a particular range of the magnitudes which depends on the number of molecules in the aggregate.

DOI： 10.1021/jp211391x

Publishing type：Research paper (scientific journal)  

The lowest excited triplet state of free-base 5,10,15-trispentafluorophenylcorrole (H(3)Cor) was studied in rigid glass by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. Triplet sublevels were experimentally determined by using magnetophotoselection and liquid crystal. Quantum chemical calculations of zero-field splitting parameters D and E were used for the sublevel assignment. The out-of-plane sublevel T(z) was found to be the lowest; namely, D is positive for H(3)Cor, in contrast to previous reports. The origin of the difference is discussed in detail. Preliminary TR-EPR experiments on rhodium corrole, accompanied by the quantum chemical calculations, emphasize the important contribution of spin-orbit couplings. (C) 2011 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.cplett.2011.11.040

Publishing type：Research paper (scientific journal)  

Herein we describe one-dimensional electron-spin arrays consisting of two different organic radicals with the designed arrangement based on the DNA sequence. Two mismatch-binding ligands carrying 2,2,6,6-tetramethylpiperidine N-oxide (TEMPO) and nitronyl nitroxide selectively bind to the predetermined sites on double stranded DNA. By using the two mismatch-binding ligands carrying the organic radicals as the glue for DNA, electron-spin assembly could be successfully synchronized with the hybridization. Periodically and tandemly arranged, two kinds of organic radical molecules at designed positions might be useful for an approach to build up scalable qubits of electron-spin-based quantum computing. The approach using DNA nanostructures as a scaffold to assembly functional small molecules can afford one of the promising ways for the future application of DNA nanostructures and nanotechnology.

DOI： 10.1002/chem.201102693

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.201204489

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.201107265

Publishing type：Research paper (scientific journal)  

Weakly exchange-coupled biradicals have attracted much attention in terms of their DNP application in NMR spectroscopy for biological systems or the use of synthetic electron-spin qubits. Pulse-ESR based electron spin nutation (ESN) spectroscopy applied to biradicals is generally treated as transition moment spectroscopy from the theoretical side, illustrating that it is a powerful and facile tool to determine relatively short distances between weakly exchange-coupled electron spins. The nutation frequency as a function of the microwave irradiation strength omega(1) (angular frequency) for any cases of weakly exchange-coupled systems can be classified into three categories; D-12 (spin dipolar interaction)-driven, Dg-driven and omega(1)-driven nutation behaviour with the increasing strength of omega(1). For hetero-spin biradicals, Dg effects can be a dominating characteristic in the biradical nutation spectroscopy. Two-dimensional pulse-based electron spin nutation (2D-ESN) spectroscopy operating at the X-band can afford to determine small values of D-12 in weakly exchange-coupled biradicals in rigid glasses. The analytical expressions derived here for omega(1)-dependent nutation frequencies are based on only four electronic spin states relevant to the biradicals, while real biradical systems often have sizable hyperfine interactions. Thus, we have evaluated nuclear hyperfine effects on the nutation frequencies to check the validity of the present theoretical treatment. The experimental spin dipolar coupling of a typical TEMPO-based biradical 1, (2,2,6,6-tetra[(2 H3) methyl][3,3-H-2(2),4-(2)H1,5,5-H-2(2)] piperidin-N-oxyl-4-yl)(2,2,6,6-tetra[(H-2(3)) methyl]-[3,3-H-2(2),4-H-2(1),5,5-H-2(2), N-15] piperidin-N-15-oxyl-4-yl) terephthalate in a toluene glass, with a distance of 1.69 nm between the two spin sites is D-12 = -32MHz (the effect of the exchange coupling J(12) is vanishing due to the homo-spin sites of 1, i.e. Delta g = 0), while 0 &lt; |J(12)| &lt;= 1.0 MHz as determined by simulating the random-orientation CW ESR spectra of 1. In addition, we have carried out Q-band pulsed ELDOR (ELectron-electron DOuble Resonance) experiments to confirm whether the obtained values for D-12 and J(12) are accurate. The distance is in a fuzzy region for the distance-measurements capability of the conventional, powerful ELDOR spectroscopy. The strong and weak points of the ESN spectroscopy with a single microwave frequency applicable to weakly exchange-coupled multi-electron systems are discussed in comparison with conventional ELDOR spectroscopy. The theoretical spin dipolar tensor and exchange interaction of the TEMPO biradical, as obtained by sophisticated quantum chemical calculations, agree with the experimental ones.

DOI： 10.1039/c2cp40778g

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.201202654

Publishing type：Research paper (scientific journal)  

We report the ferromagnetic ordering phenomena occurring in organic molecular crystals with structural chirality. Achiral radical 1 has been found to crystallize in two enantiomorphs with chiral space groups of P4(3) and P4(1). The P4(3) form (1L) has left-handed stacking of the molecules, giving the helical chirality in a crystalline solid. In the other form of P4(1) (1R), the right-handed stacking corresponds to a mirror image of IL. Magnetic susceptibility measurements show that both the crystals undergo a ferromagnetic phase transition at T(C) = 1.1 K. The ferromagnetic ordering has been confirmed by heat capacity measurements. The magnetic heat capacity exhibits lambda-shaped peak at T(C) = 1.1 K with an entropy change of R ln 2, as expected for S = 1/2 spins. This is the first example of genuinely organic molecule-based ferromagnetism associated with the structural chirality based on the helical molecular packing in the crystalline solid.

DOI： 10.1021/jz2014105

Publishing type：Research paper (scientific journal)  

A calix[4] arene-based biradical with two tert-butyl nitroxide radicals and a monoradical derived from the biradical have been studied by continuous-wave electron spin resonance (CW-ESR) and pulse-ESR-based hyperfine sublevel correlation (HYSCORE) spectroscopy. The two nitroxide radical sites antiferromagnetically interact with each other, generating a thermally accessible triplet state located 4 cm(-1) above the singlet ground state. The present fine-structure and hyperfine spectral simulation for the spin Hamiltonian parameters of the biradical is sensitive to the local molecular structure at the spin-bearing site, illustrating a salient electronic structure of the radical sites with the pi-orbitals on the nitrogen (and oxygen) atoms cross-facing each other. The derived structure contrasts with the molecular structure determined by an X-ray crystal analysis for the hydroxylamine precursor of the biradical. The distance between the two midpoints of the nitrogen-oxygen bonds at the radical sites is by 0.234 nm longer than the one (=0.314 nm) of the two hydroxyl groups of the precursor determined by the X-ray analysis. The lack of intramolecular hydrogen bonds between the nitrogen and hydrogen of the hydroxyl groups, caused by the oxidation of the hydroxyamino precursor, gives rise to such a sizable increase in the distance between the radical sites. The HYSCORE experiments gave a direct evidence of the local molecular structure of the radical site of the partially oxidized monoradical. The experimentally derived molecular structures of both the bi-, monoradicals and the precursor are in good agreement with those obtained by density functional theory calculations.

DOI： 10.1007/s00723-011-0269-6

Publishing type：Research paper (scientific journal)  

DOI： 10.1038/NMAT3142

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/cphc.201100489

Publishing type：Research paper (scientific journal)  

We have prepared and isolated neutral polycyclic hydrocarbon radicals. A butyl-substituted radical gave single crystals, in which a pi-dimeric structure, not a a-bonded dimer, was observed, even though steric protection was absent. Thermodynamic stabilization due to the highly spin-deloralind structure contributes effectively to the suppression of a-bond formation.

DOI： 10.1021/ja2065768

Publishing type：Research paper (scientific journal)  

Complex formation of quaterimidazole with Fe-II, Co-II, and Ni-II yielded dinuclear triple helicates in the solution state by the self-assembling ability of the ligand based on the strong chelating coordination bonds. Crystallization of the Co-II complex from aqueous solution afforded the Co-III complex with a triple-helical structure. X-ray crystal structure analyses revealed that the helicates are linked through N-H center dot center dot center dot X hydrogen bonds with counteranions and solvent molecules to form three-dimensional networks. The spectrophotometric titration experiment showed that quaterimidazole forms triple helicates with various d-block transition metal ions with high selectivity. The outward intermolecular interactions and high stability of the helicates from the rigid molecular structures combined with the intramolecular pi-pi interactions of imidazole moieties and their strong chelating coordination enabled the successful optical resolution of right- and left-handed helicates by chiral-column HPLC.

DOI： 10.1002/ejic.201100488

Publishing type：Research paper (scientific journal)  

Green beans and roasted beans of coffee with Rio flavor were analyzed by gas chromatography-olfactometry to clarify the causal substances of Rio flavor in Brazilian coffee. In addition to 2,4,6-trichloroanisole (TCA) and 2,4,6-trichlorophenol (TCP), which are known as the main causal substances of Rio flavor, a new iodine-like flavor-causing compound, 2,6-dichlorophenol (DCP), was detected. The detected amounts of 2,6-DCP and 2,4,6-TCA were less than 0.1 and 0.1 ppb in Rio flavor-free coffee beans, 0.8 and 1.2 ppb in weak Rio flavored beans, and 3.0 and 2.6 ppb in strong Rio flavored beans, respectively. Musty and chlorine flavors were sensed more strongly in model coffee containing both 2,4,6-TCA and 2,6-DCP than in the coffee containing them individually. In the present study, 2,6-DCP was identified as a new causal substance of Rio flavor, and it was found that the presence of 2,4,6-TCA intensifies Rio flavor, as a synergy effect.

DOI： 10.3136/fstr.17.347

CiNii Article

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

A new 2,5-di-tert-butyl-6-oxophenalenoxyl (6OPO) derivative with a cyano group at the 8-position, where a large spin density resides, has been synthesized. This neutral radical exhibits high stability in the solid state in air despite the low steric protection on the 8-position; the stability is comparable to that of a corresponding 8-tert-butylated 6OPO derivative. EPR/(HENDOR)-H-1/TRIPLE (electron paramagnetic resonance/H-1-electron-nuclear double resonance/TRIPLE) spectroscopy and cyclic voltammetry showed an extended spin delocalization on the cyano group and a significant increase in electron-accepting ability relative to that of the 8-tert-butylated 6OPO derivative. DFT calculations indicated the extension of a singly occupied molecular orbital (SOMO) onto the cyano group and the lower-lying SOMO and LUMO in comparison with those of the 8-tert-butylated 6OPO derivative, which was consistent with experimental results. Furthermore, the extended nature of p conjugation onto the cyano group was quantitatively evaluated by calculating the contributing weights of resonance structures in terms of a molecular orbital (MO)-based valence-bond (VB) method. Herein, the synthesis and physical properties of the 8-cyano-6OPO derivative are described, emphasizing that the high stability arises from the electronic effect of the cyano group. Also, the usefulness of the quantitative resonance structure analysis is shown.

DOI： 10.1002/asia.201000793

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

Electron and nuclear spins as quantum bits (qubits) have been the focus of current issues in quantum information science/technology and related fields. From the viewpoint of chemistry, synthetic spin qubits are emerging. Diphenylnitroxide (DPNO) and its novel fluorine substituted radicals are characterized as synthetic electron bus spin-qubits by continuous-wave ESR and H-1-, F-19-ENDOR/TRIPLE spectroscopy in solution and by DFT calculations The partially fluorinated DPNOs have been synthesized to illustrate that they are candidates for the synthetic bus spin-qubits with well-defined client qubits. The fluorinated DPNOs undergo spin delocalization; dominating the robust spin polarization in the pi-conjugation of phenyl rings, serving to increase the number of distinguishable client qubits from three to six.

DOI： 10.1021/jz101650z

Publishing type：Research paper (scientific journal)  

DOI： 10.1038/NCHEM.985

Publishing type：Research paper (scientific journal)  

Graphene, a two-dimensional layer of sp2-hybridized carbon atoms, can be viewed as a sheet of benzene rings fused together. Three benzene rings can be combined in three different ways, to yield linear anthracene and angular phenanthrene, where the rings share two C-C bonds, and the phenalenyl structure where three C-C bonds are shared between the rings. This third structure contains an uneven number of carbon atoms and, hence, in its neutral state, an uneven number of electrons - that is, it is a radical. All three structures may be viewed as being sections of graphene. Extension of this concept leads to an entire family of phenalenyl derivatives - 'open-shell graphene fragments' - that are of substantial interest from the standpoint of fundamental science as well as in view of their potential applications in materials chemistry, in particular quantum electronic devices. Here we discuss current trends and challenges in this field. © 2011 Macmillan Publishers Limited. All rights reserved.

DOI： 10.1038/nchem.985

PubMed

Publishing type：Research paper (scientific journal)  

CiNii Article

Publishing type：Research paper (scientific journal)  

Dimethylmethylenebis(iminonitroxide) diradical <b>1</b> was prepared from 3-hydroxy-2,2-dimethylpropanal in five steps. The structure, ESR spectrum, and magnetic properties are reported: <b>1</b> exhibited an antiferromagnetic interaction of <i>J</i>/<i>k</i>_B = −72 K (<b><i>H</i></b> = −2<i>J</i><b>S</b>₁·<b>S</b>₂).

DOI： 10.1246/cl.2011.22

CiNii Article

Publishing type：Research paper (scientific journal)  

Organic high-spin molecules have attracted continuing attention as important building blocks of molecule-based magnets. Nitronyl nitroxide radical (<B>NN</B>), imino nitroxide radical (<B>IN</B>) and tert-butyl nitroxide radical (<B><SUP><I>t</I></SUP>BuNO</B>) have been well studied as components of organic high-spin molecules because of their stabilities and metal-complexation abilities. For the creations of new high-spin building blocks with extraordinary strong intermolecular spin-spin interactions, we have designed and synthesized a directly-linked (nitronyl nitroxide)-nitroxide diradical (<B>NN-<SUP><I>t</I></SUP>BuNO</B>) and (imino nitroxide)-nitroxide diradical (<B>IN-<SUP><I>t</I></SUP>BuNO</B>). These diradicals are very stable even in aerated conditions. ESR spectra in frozen diethyl phthalate at low temperature showed clearly spin-allowed and spin-forbidden transition signals assigned to triplet species of diradicals. The measurements of magnetic susceptibility demonstrated that the diradical are in a triplet ground state with a large intramolecular exchange interaction.

DOI： 10.11494/kisoyuki.2010.0.2P50.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Phenalenyl is an odd-alternant hydrocarbon neutral radical having a planar condensed polycyclic pi-electronic structure. The electronic-spin of phenalenyl is extensively delocalized over the whole molecular skeleton. We have designed and synthesized various kinds of air-stable phenalenyl radical derivatives, and experimentally demonstrated their exotic magnetic, electronic, and optical properties inherently attributable their unique spin-delocalized nature. Recently, these results inspired us to design the first optically-active phenalenyl radicals bearing a helicenic structure. In this study, we have succeeded in the synthesis and isolation, and evaluated the electronic-spin structure and racemization behavior.

DOI： 10.11494/kisoyuki.2010.0.3P65.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Phenalenyl is an odd-alternant hydrocarbon neutral radical having a planar condensed polycyclic pi-electronic structure. We have designed and synthesized various kinds of air-stable phenalenyl radical derivatives and experimentally demonstrated their exotic magnetic, electronic, and optical properties inherently attributable to their unique spin-delocalized nature. Recently, these results inspired us to design the first optically-active phenalenyl radicals possessing helicenic structure. In this study, we have succeeded in the synthesis and isolation of the chiral phenalenyl radical as an air-stable solid. The electronic-spin structure, chiroptical properties, and racemization behavior were experimentally evaluated.

DOI： 10.11494/kisoyuki.2011.0.168.0

CiNii Article

Publishing type：Research paper (scientific journal)  

We have recently reported that (nitronyl nitroxide)-substituted dihydrophenazine radical cations exhibit interesting magnetic properties. For further development of this system, we have designed and synthesized a neutral dihydrophenazine derivative with two nitronyl nitroxides at 2,7-positions and its oxidized cationic species. We clarified 1) the neutral diradical species shows a weak ferromagnetic interaction between the two nitronyl nitroxides, 2) the cationic species exhibits a strong ferromagnetic interaction between the dihydrophenazine radical cation and the two nitronyl nitroxides. The structures and properties of these species will be described.

DOI： 10.11494/kisoyuki.2011.0.162.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Trioxotriangulene (TOT) is a neutral pi-radical having 25-pi electronic system established by oxo-substitution and two-dimensional pi-extension of phenalenyl system. The <I>tert</I>-butyl derivative TOT(<I>t</I>-Bu)<SUB>3</SUB> is highly stable under air, and exhibits intriguing functions based on the multi-stage redox ability and self-assembling ability. The chemical modification on TOT system is a promising chemical approach to control the electronic and structural properties, and to demonstrate new functions. In the present study, we have designed and synthesized halogenated derivatives of TOT, and their physical properties were investigated focusing on the substituent effects by means of electrochemical, structural, and magnetic measurements.

DOI： 10.11494/kisoyuki.2010.0.B09.0

CiNii Article

Publishing type：Research paper (scientific journal)  

We have recently reported that radical-substituted trioxytriphenylamine (<B>TOT</B>) radical cation salts exhibit interesting magnetic properties such as weakferromagnetic phase transition. For the development of the <B>TOT</B> system, we have designed a (tri-<I>t</I>-butylnitroxide)-substituted <B>TOT</B> derivative, whose one electron-oxidation product is expected to have a triplet ground state. The one-electron oxidation product is obtained by treatmentum with a chemical oxidant such as thianthrene radical cation or triphenylamine radical cation. The ESR spectrum of this species in frozen diethyl phthalate showed a spin-allowed and a spin-forbidden transition signals assigned to triplet species. The syntheses and magnetic properties of the neutral triradical and its one-electron oxidized species are reported in detail.

DOI： 10.11494/kisoyuki.2010.0.2P51.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Trioxotriangulene (TOT) is a fused polycyclic neutral radical with a planar 25 pi-electronic structure. We revealed that TOT derivatives possessing alkyl or alkoxy groups and halogen atoms are extremely stable under air atmosphere in both solid and solution states and exhibit exotic magnetic, electronic, and electrochemical properties due to the extensive spin-delocalized nature and degenerated LUMOs. In this work, in order to explore a new aspect of the TOT chemistry, we have newly designed, synthesized, and isolated TOT derivatives bearing thiophene moieties. The stability, redox properties, and electronic-spin structure have been experimentally investigated.

DOI： 10.11494/kisoyuki.2011.0.167.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Synthesis and elucidations of molecular and electronic-spin structures of novel stable neutral radical derivatives are fundamentally important issues for the development of spin-mediated molecular functional materials. From this viewpoint, we investigate trioxotriangulene (TOT) derivatives, a neutral radical with fused polycyclic pi-conjugated system. We experimentally revealed high stability in air and four-step redox ability of the TOT derivative possessing three <I>t</I>-butyl groups. In order to gain further insight into TOT system, we focused on substituent effects of this system and designed TOT derivatives possessing electron-donating /-withdrawing groups. Recently, we have successfully synthesized and isolated TOT derivatives with three <I>n</I>-butoxy groups. In this study, The substituent effects of these derivatives on the cristal structures and magnetic properties have been studied by X-ray analysis and magnetic measurements.

DOI： 10.11494/kisoyuki.2010.0.2P52.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Recently, pi-conjugated compounds containing typical elements other than carbon, nitrogen and oxygen atoms have attracted much attention because they have unique electronic and photophysical properties. Diarylamine substituted boranes are interesting compounds in the view point of B-N double bond character and its influence on the molecular properties. We have succeeded in synthesizing of borane derivatives substituted two or three diarylamine moieties including phenothiazine and dihydrophenazine. These compounds are easily oxidized and give stable radical cations in the crystalline states. We here report their structures and properties.

DOI： 10.11494/kisoyuki.2011.0.326.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Trianionic spin-quartet and tetraanionic spin-quintet molecular clusters derived from m-dibenzoylbenzene in solution were identified by CW-ESR/pulse-ESR based two-dimensional electron spin transient nutation spectroscopy, and their spin and clustering structures in the ground state were determined in terms of a D-tensor based phenomenological approach and DFT calculations. The molecular structures obtained semiempirically are supported by DFT-based quantum chemical calculations. The DFT calculations have been tested for a sodium ion bridged fluorenone-based cluster, [fluorenone(-center dot) {Na+(dme)(2)}](2), whose crystal structure was reported in the literature [H. Bock, H.-F. Herrmann, D. Fenske and H. Goesmann, Angew. Chem., Int. Ed. Engl., 1988, 27, 1067], reproducing the experimentally determined moelcular structure of the dimer cluster. It is suggested that both the quartet and quintet clusters in the 2-MTHF glass and solution form the cross-typed structures with the two m-dibenzoylbenzene moieties in cis-configuration. A dianionic spin-triplet m-dibenzoylbenzene derivative was detected for the first time and its charge and spin densities were studied by the quantum chemical calculations. The high-spin states of the open-shell entities under study were confirmed by X-band pulse-ESR based electron spin nutation spectroscopy in organic frozen glasses. The D values and other spin Hamiltonian parameters of all the polyanionic high-spin species were determined by the hybrid eigenfield spectral simulation for fine-structure ESR spectra. m-Dibenzoylbenzene provides pseudo-degenerate pi-LUMOs arising from its topological symmetry of the pi-electron network and its dianion in the triplet ground state is a prototypical model for topologically-controlled genuinely organic ferromagnetic metals.

DOI： 10.1039/c0cp00730g

Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c0cp02809f

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

DOI： 10.1038/nmat3142

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

We report on the highly compact nitroxide-substituted nitronyl nitroxide 1 and iminonitroxide 2; they have isoelectronic structures with trimethylenemethane. These diradicals are stable under aerated conditions at room temperature and have large positive exchange interactions: J/k(8) = +390 K (H = 2,JS(1/2)center dot S-1/2) for 1 and J/k(B) approximate to +550 K for 2.

DOI： 10.1021/ja107769z

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

Symmetric hexaazaphenalenes (R = phenyl and tert-butyl) have been synthesized by one-pot condensations of corresponding amidine hydrochlorides with tricyanomethanide. The hexaazaphenalenes are linked with each other by a N-H center dot center dot center dot N hydrogen-bonding interaction in the crystalline states. Interestingly, a planar and achiral tert-butylated derivative was crystallized in a chiral space group with assembly of one-handed helical hydrogen-bonded chains. Hexaazaphenalenyl anions were isolated as air- and water-stable tetraethyl ammonium salts.

DOI： 10.1021/ol102200v

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A novel naphthoquinoid singlet biradical (2a) stabilized by phenalenyl rings is prepared by a multistep procedure and is investigated in terms of covalent bonding interactions. The molecule 2a gives single crystals, in which a 1D chain is formed with a very short pi-pi contact at the overlapping phenalenyl rings. The unpaired electrons in 2a are involved in covalent bonding interactions not only within the molecule but also between the molecules in the 1D chain, and a linear conjugation is made of the alternating intra and intermolecular covalent bonding interactions through conventional pi-conjugation and multicenter bonding, respectively. The linear conjugation causes a lower-energy shift of the optical transition band in the crystal, but the transition energy is higher than that of the benzoquinoid singlet biradical (la). This optical behavior and the magnetic susceptibility measurements reveal that the intermolecular covalent bonding interaction in the 1D chain of 2a is greater in strength than the intramolecular one, despite the fact that a fully conjugated Kekule structure can be drawn for 2a.

DOI： 10.1021/ja1037287

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

Zero-field splitting (wZFS) tensors (D tensors) of organic high-spin oligonitrenes/oligocarbenes up to spin-septet are quantitatively determined on the basis of quantum chemical calculations. The spin-orbit contributions, D(SO) tensors are calculated in terms of a hybrid CASSCF/MRMP2 approach, which was recently proposed by us. The spin-spin counterparts, D(SS) tensors are computed based on McWeeny-Mizuno&apos;s equation in conjunction with the RODFT spin densities. The present calculations show that more than 10% of ZFS arises from spin-orbit interactions in the high-spin nitrenes under study. Contributions of spin-bearing site-site interactions are estimated with the aid of a semi-empirical model for the D tensors and found to be ca. 5% of the D(SO) tensor. The analysis of intermediate states reveal that the largest contributions to the calculated D(SO) tensors are attributed to intra-site spin flip excitations and delocalized pi and pi* orbitals play an important role in the inter-site spin-orbit interactions.

DOI： 10.1002/cphc.201000492

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A teranthene derivative has been successfully isolated in a crystalline form for the first time. Geometrical considerations and physical property investigations indicate that the molecule possesses prominent biradical character in the ground state.

DOI： 10.1021/ja1049737

Publishing type：Research paper (scientific journal)  

We have synthesized and characterized a new G–G mismatch binding ligand containing a TEMPO radical. The two mismatch binding ligands cooperatively bound to the CGG/CGG triad and an apparent binding constant was in the order of 10⁵ M⁻¹. The tumbling of the ligand on a DNA duplex was ten times slower than that of the unbound ligand. Asymmetric addressability of two TEMPO radicals on DNA is shown.

DOI： 10.1246/cl.2010.556

CiNii Article

Publishing type：Research paper (scientific journal)  

We have first achieved the synthesis of triple-stranded metallo-helicates composed of 4,4':2',2 '':4 '',4 '''-quaterimidazole (Qim) and Mn(II) or Zn(II) ions, which serve as synthetic electron spin qubits (quantum bits). In the crystal structure, a hydrogen-bonding network through counteranions and/or crystal solvents was constructed by the outward N-H hydrogen-bonding functional groups intrinsic to the imidazole skeleton. Importantly, these helicates showed high stability even in a solution state at room temperature. These salient features of triple helicates of Qim are different from those of reported metallo-helicates. These chemical properties of the Qim-based triple helicates allow us to synthesize magnetically diluted single crystals composed of Mn(II) (S = 5/2) and diamagnetic Zn(II) complexes of Qim in an appropriate Mn(II)/Zn(II) ratio. The magnetically diluted crystals can afford to build up the prototype of electron-spin qubits of Lloyd's one-dimensional periodic system, which gives a practical approach to scalable quantum computers/quantum information processing systems (QCs/QIPSs). The experiments have proven the practical capability of oligo(imidazole)s as a component of Lloyd's system which has nonequivalent g-tensors within the helicate (g-engineering). The helical symmetry plays an important role in giving a prototype of the synthetic spin qubits of the formidable Lloyd model. This result links supramolecular chemistry to the field of QCs/QIPSs.

DOI： 10.1021/ja102030w

Publishing type：Research paper (scientific journal)  

Radical-substituted radical cation salts are exotic species that are potentially applicable as spin building blocks for molecular magnets. We recently found that these species, which are derived from a diphenyldihydrophenazine (DPP) framework, are stable under aerated conditions at room temperature. Of these species, nitronyl nitroxide (NN(center dot))-substituted DPP(center dot+) tetrachloroferrate (NNDPP(center dot center dot+)center dot FeCl(4)(-)) showed antiferromagnetic interaction at low temperature (&lt;150 K), whereas the tetrabromoferrate salt NNDPP(center dot center dot+)center dot FeBr(4)(-) exhibited a magnetic phase transition at 6.7 K to produce a bulk ferrimagnet. Both salts had very similar molecular structures. The difference in the magnetic properties was ascribed to the difference in molecular packing structures. A significant difference in these two salts was observed at the (NNDPP(center dot center dot+))-(NNDPP(center dot center dot+)) intermolecular contact, including the oxygen atom of the nitroxide moiety; NNDPP(center dot center dot+)center dot FeCl(4)(-) had a serious antiferromagnetic O-O (nitroxide oxygen, 3.02 angstrom) intermolecular contact, whereas NNDPP(center dot center dot+)center dot FeBr(4)(-) had a ferromagnetic O-HC (2.53 angstrom) intermolecular contact.

DOI： 10.1351/PAC-CON-09-10-04

Publishing type：Research paper (scientific journal)  

A trimethylenemethane (TMM) derivative 1(2+) in which the parent TMM is pi-extended by the symmetric insertion of three pyridine rings into the C-C bonds of TMM, has been synthesized by the alkali metal reduction of the isolated corresponding dication. Although the frozen-glass X-band cw-ESR spectrum of 1(2+) gave unresolved fine structures due to the small ZFS parameters, pulsed ESR two-dimensional electron spin transient nutation (2D-ESTN) spectroscopy unambiguously can afford to identity diradical 1(2+) as a triplet species.

DOI： 10.1021/ol902937k

CiNii Article

J-GLOBAL

Publishing type：Research paper (scientific journal)  

In high-spin chemistry, random-orientation fine-structure electron paramagnetic resonance (FS ESR) spectroscopy holds the advantages of the most facile and convenient method to identify high-spin systems. The FS ESR spectroscopy for high spins in frozen rigid glasses has seemingly been well established since the first spin-quintet m-dicarbene and m-dinitrene appeared in 1967. The FS ESR spectra of organic quintet entities generated by photolysis in the 2-methyltetrahydrofuran (2-MTHF) glass, however, have never been fully analyzed due to a peculiar line broadening appearing at many canonical peaks. The line broadening has been a notorious obstacle that masks key FS transitions of many cases in organic glasses or argon matrices. We examine the origin of the line broadening, illustrating the comprehensive spectral analysis for m-dinitrenes and other types of typical quintet-state dinitrenes observed in the 2-MTHF glass. Our new approach to the line broadening analysis invokes both exact analytical solutions for the resonance fields of canonical peaks and a magnetic-parameter gradient method. We have derived the exact analytical expressions for FS canonical peaks for high-spin states, for the first time. A microscopic origin of the line broadening observed for high-spin nitrenes generated by photolysis in rigid glasses is proposed on the basis of quantum chemical calculations of the D-tensor.

DOI： 10.1007/s00723-009-0056-9

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.201002626

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.200906666

PubMed

J-GLOBAL

Publishing type：Research paper (scientific journal)  

Nitronyl nitroxide radical introduced to naphthyridine carbamate dimer is noncovalently bound to a CGG/CGG triad as an addressable position in DNA duplexes, leading to the programmed assembly of the radical molecules into an 11-mer duplex and a tandem repetitive array of double stranded DNA.

DOI： 10.1039/b913061f

Publishing type：Research paper (scientific journal)  

As a novel radical building block possessing multiple hydrogen bond functionality, we have designed and synthesised diaminotriazine-substituted nitronyl nitroxide (DAT-NN; 1). The diaminotriazine moiety of 1 forms two kinds of hydrogen bonding and molecule 1 forms an S = 1/2 uniform antiferromagnetic Heisenberg chain with the exchange interaction of J/k(B) = -15.3 K in the crystalline solid, which is attributable to close contacts between the nitronyl nitroxide oxygen atoms. H-1-ENDOR spectroscopy has shown that the triazine moiety has little significant spin density. Thus, the diaminotriazine moiety plays a role primarily in determining the molecular packing instead of propagating intermolecular magnetic interactions in the crystalline solid.

DOI： 10.1039/b909757k

Publishing type：Research paper (scientific journal)  

A new corannulene-based curved neutral pi-radical bearing a tert-butylnitroxide moiety has been synthesized and isolated as an air-stable solid. Direct attachment of the spin centre to the corannulene skeleton gives rise to an extensive spin-delocalization onto the curved pi-conjugated system from the nitroxide moiety. This salient electronic feature in the curved neutral radical system and its high stability have allowed us to find a dynamic electronic-spin behaviour induced by the temperature-dependent conformational change of the nitroxide moiety, as studied by liquid-phase variable-temperature electron spin resonance and (1)H electron-nuclear double resonance and electron-nuclear-nuclear triple resonance spectroscopies with the help of density functional theory calculations.

DOI： 10.1071/CH10280

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

In high-spin chemistry, random-orientation fine-structure (FS) electron spin resonance (ESR) spectroscopy entertains advantages as the most facile and convenient method to identify high-spin systems, as frequently reported in the literature. Random-orientation ESR spectroscopy applicable to organic high-spin entities can date back to the Wasserman and co-workers&apos; attempt on the first spin-quintet dicarbene, m-phenylenebis-(phenylmethlene) (m-PBPM), in the 2-MTHF glass in 1963 and 1967, following their Successful work on randomly oriented triplet-state ESR spectroscopy. The FS ESR spectrum of m-PBPM in the 2-MTHF glass, however, has never fully been analyzed due to a peculiar line-broadening appearing at many canonical peaks. Organic high-spin spectra from most quintet dinitrenes also suffer from similar phenomena. Seemingly intrinsic line-diffusing or -broadening phenomena adversely affect the reliable determination of FS parameters for organic high-spin entities in rigid glasses. In high-spin chemistry, the line-broadening has been,in obstacle that masks key FS transitions in many cases. Thus, both the origin of the broadening and the comprehensive spectral analysis have been a long-standing issue. In this report, we examine the origin of the line-broadening of appearing in the FS ESR spectra, illustrated by a comprehensive spectral analysis for m-PBPM in the quintet ground state and the first-documented quintet-state dinitrene, m-phenylenebis(nitrene) (m-PBN) in the 2-MTHF glass. A complete analysis of the random-orientation FS spectra from m-PBPM diluted in the benzophenone crystal has shown that the g-anisotropy of m-PBPM is not prominent. Also the higher-order FS terms Such as S(i)(2)S(j)(2) group-theoretically allowed for S = 2 are not necessary in spite of the argument for a hydrocarbon-based tetraradical (S = 2) in the ground state. Our new approach to the line-broadening analysis invokes both exact analytical solutions for the resonance fields of canonical peaks and the magnetic-parameters gradient method. The D- and E-values of m-PBPM acquired by the spectral simulation in this Study give different molecular structures of the quintet dicarbene in the benzophenone crystal lattice (D = +0.0703(0) cm(-1), E = +0.0212(0) cm(-1)) and in the 2-MTHF glass (D = +0.0780(0) cm(-1), E = +0.0221(0) cm(-1)). Microscopic origins of the line-broadening observed for high-spin oligocarbenes or oligonitrenes generated by photolysis in organic glasses have been proposed.

DOI： 10.1021/jp9042717

CiNii Article

J-GLOBAL

Publishing type：Research paper (scientific journal)  

The spin-orbit contributions (D(50) tensors) to the zero-field splitting tensors (D tensors) in the excited triplet states of CS(2) and diazabenzenes are investigated by using the sum-over-states formula with the CASSCF spin-orbit coupling matrices and the CASSCF or MRMP2 energies. The D(50) tensor calculated using the CASSCF energies is in some cases far from the experiment due to inaccurate energy differences, but the discrepancy can be circumvented by replacing the CASSCF energies with the MRMP2 ones. Effects of the geometry relaxation in the excited states on the D tensors are also discussed. (C) 2009 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.cplett.2009.07.007

Publishing type：Research paper (scientific journal)  

A new pyrene-dihydrophenazine dyad was prepared. Oxidation of the neutral species produced a bis(radical cation) species, which was characterized by the absorptions of their component radical cations in the visible region. A thermally accessible triplet state was observed in the ESR measurement in frozen n-PrCN, The energy gap between the singlet and triplet states was determined to be 2J/k(B) = -36 +/- 3 K.

DOI： 10.1021/ol9009927

PubMed

J-GLOBAL

Publishing type：Research paper (scientific journal)  

A triamine, 2,2&apos;,4,4&apos;-tetrabromo-3 &apos;&apos;,4 &apos;&apos;-dimethyl-5,5&apos;-bis(di(4-methylphenyl)amino)triphenylamine, was designed and synthesized as a model precursor for purely organic cationic high-spin systems. Cyclic voltammetry measurements revealed that the triamine gives stable mono-, di-, and tricationic states at ambient temperature. Novel electron transfer stopped-flow (ETSF) methods were invoked for characterizing the absorption spectra of the corresponding mono- and oligo-cationic states. The triamine-based trication was generated by chemical oxidation at room temperature, and the triamine was quantitatively recovered upon reduction. The electronic ground state of the trication is discussed. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2008.10.023

Publishing type：Research paper (scientific journal)  

A starburst-shaped ligand, 4,4&apos;4 &apos;&apos;-tris[N, N-bis(2-pyridylmethyl) aminomethyl] triphenylamine, and its palladium and copper trinuclear complexes were designed and prepared. NMR techniques, COSY and ROESY, were applied to the palladium complex to examine its conformation in solution. The palladium complex was found to prefer a folded conformation even at 75 degrees C, indicating the occurrence of strong intramolecular stacking interaction. CV measurements of the palladium complex showed reversible TTA/TTA(+) redox couples. ETSF measurements showed that the corresponding radical pendant complex is very unstable. Molecular design rules for triarylamine-based spin bearing ligands are discussed. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2008.11.001

Publishing type：Research paper (scientific journal)  

New oxoverdazyl (Vz)-substituted dihydrophenazine radical cations (DPP center dot+) MCl4- (M=Ga, Fe) salts were prepared. The molecular and packing structures, the intramolecular exchange interactions, and the magnetic properties were investigated. The organic part (VzDPP(center dot center dot+)) showed a sizable intramolecular ferromagnetic interaction of J/k(B) &gt;= +250 K (H = -2JS(Vz) S-DPP) between Vz(+) and DPP center dot+, giving S = 1 state at room temperature. Both compounds had very similar molecular and packing structures and there were several intermolecular short contacts between the magnetically important atoms. A 2D type sheet structure was constructed through the contacts between VzDPP(center dot center dot+) and MCl4- moieties in the b-c* plane and a linear ladder chain structure was observed in the a*-direction through the contacts between VzDPP(center dot center dot+) moieties. Thus, the overall intermolecular contacts extend in a 3D manner. The chi T-p value gradually decreased by lowering the temperature, indicating anti ferromagnetic interactions in both salts. From the temperature dependence of chi T-p with consideration of the crystal packing structures, the antiferromagnetic interaction between the VzDPP(center dot center dot+) spins within the ladder chain was estimated to be in the order of -30 K for VzDPP(center dot center dot+) center dot GaCl4-. A similar antiferromagnetic interaction between the VzDPP(center dot center dot+) spins within the ladder chain and a slightly weaker antiferromagnetic interaction between the Fe(III) spins through the ladder chain were observed for VzDPP(center dot center dot+) center dot FeCl4-. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2008.11.002

Publishing type：Research paper (scientific journal)  

Three highly pi-extended tetraaryl-1,3-phenylenediamines for charged high-spin molecular systems were successfully synthesized using Suzuki coupling. Their electrochemical and spectroscopic properties were also examined. They showed blue fluorescence. The dications derived from highly pi-extended tetraaryl-1,3-phenylenediamines were generated and characterized by electron transfer stopped-flow method. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2008.11.027

Publishing type：Research paper (scientific journal)  

Radical-substituted radical cations are attractive spin building blocks of molecule-based magnets. The introduction of an additional spin as a counteranion provides a unique three-spin system wherein the magnetic interactions between the spins of the radical substituent and the radical cation J(intra)) and those between the spins of the radical cation and the anion (J(inter)) play decisive roles in determining the magnetic properties of the system. We report the first demonstration of a ferrimagnet by utilizing a large-J(intra) system, nitronyl nitroxide-substituted dihydrophenazine, radical cation (NNDPP center dot+) in combination with tetrabromoferrate (FeBr4-) as the counteranion. On the basis of measurements of dc and ac magnetic susceptibilities and heat capacity, the magnetic properties of NNDPP center dot+center dot FeBr4- are elucidated to be those of a three-dimensional long-range-ordered ferrimagnet with T-c = 6.7 K.

DOI： 10.1021/ja808093z

PubMed

J-GLOBAL

Publishing type：Research paper (scientific journal)  

Mononuclear copper (II)-superoxo complexes 2(X)-OO(center dot) having triplet (S = 1) ground states were obtained via reaction Of O(2) with the copper(I) starting materials 1(X) supported by tridentate tigands L(X) [1-(2-p-X-phenethyl)-5-(2-pyridin-2-ylethyl)-1,5-diazacyclooctane; X = CH(3), H, NO(2)] in various solvents. The superoxo complexes 2(X)-OO(center dot) mimic the structure [tetrahedral geometry with an end-on (eta(1))-bound O(2)(center dot-)] and the aliphatic C-H bond activation chemistry of peptidylglycine alpha-hydroxylating monooxygenase and dopamine beta-monooxygenase.

DOI： 10.1021/ja809464e

J-GLOBAL

Publishing type：Research paper (scientific journal)  

CiNii Article

Publishing type：Research paper (scientific journal)  

In connection with our previous study of (nitronyl nitroxide)-substituted dihydrophenazine radical cation tetrabromoferrate, we report preparation and magnetic property of (nitronyl nitroxide)-substituted trioxytriphenylamine radical cation tetrachloroferrate (NNTOT+FeCl4-) and tetrachlorogallate (NNTOT+GaCl4-). NNTOT+FeCl4- exhibitted a successive phase transition at 2.9 K and 0.8 K. The higher temperture transition is due to the organic NNTOT+ magnets, whereas the lower one involves Fe(III) spins.

DOI： 10.11494/kisoyuki.2009.0.60.0

CiNii Article

Publishing type：Research paper (scientific journal)  

According to a quantum chemical calculation(BLYP/6-31G**//B3LYP/6-31G**), the spin density of anthroxyl reaches a maximum at the position of 10, not at the oxygen atom. Very recently, we have synthesized biradicals, having two anthroxyl radicals and an athracene moiety to reveal electronic structure of anthroxyl radicals. This biradicals are extremely stable, even though they are treated with polar-protic solvents such as ethanol and water. We elucidated the molecular structures with X-ray analyses and the electronic properties by ESR, SQUID, cyclic voltamogram and UV-VIS spectra. Here we report these fundamental prperties and the study of more larger acene systems to which anthroxyls are conenected.

DOI： 10.11494/kisoyuki.2009.0.149.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Organic high-spin molecules are important spin building blocks in materials science. In connection with our studies for the development of new magnetic materials using radical-substituted radical ions, we have designed and synthesized a new neutral diradical (NN-tBuNO) by combination of typical stable radicals, nitronyl nitroxide (NN) and tert-butyl nitroxide (tBuNO). NN-tBuNO was stable under aerated conditions at room temperature in the crystalline state and exhibited a spin-allowed and a spin-forbidden transition EPR signals in frozen butyronitrile. The magnetic susceptibility measurement showed a large intramolecular ferromagnetic interaction between NN and tBuNO. Synthesis, structure, magnetic properties, and preparation of metal complexes will be reported.

DOI： 10.11494/kisoyuki.2009.0.231.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Pulse-based Electron-Nuclear and ELectron-electron DOuble Resonance (ENDOR/ELDOR) techniques have been applied to molecular spins in order to implement ensemble electron spin-qubit based quantum computers/computing (QC) and quantum information processing (QIP) in the solid state. Pulsed ENDOR-based QC/QIP experiments for super dense coding (SDC) have for the first time been carried out by the use of molecular electron-and nuclear-spin entities such as the stable malonyl radical as matter spin-qubits. The spin-qubit manipulation technology for quantum gate operations in this work is based on the time-proportional-phase-increment (TPPI) technique, enabling us to distinguish between the phases of spin-qubit based entangled states. The TPPI technique, as firstly applied by Mehring et al. (M. Mehring, J. Mende and W. Scherer, Phys. Rev. Lett., 2003, 90, 153001), has illustrated the establishment of quantum entanglement between electron-and nuclear-spin states and mutual interconversion between the electron-nuclear Bell states. The electron-spin 4 pi-periodicity in phase shows up in the QC/QIP experiments, explicitly and experimentally illustrating the electronspin spinor nature for the first time. Tripartite QC experiments have been made, showing the occurrence of separable states. Also, the development of novel electron-spin technology to manipulate multi-electron spin-qubits is described. In this work, the pulsed coherent-dual ELDOR for QC/QIP has for the first time been implemented by invoking a novel microwave dual phase-rotation technique. Thus, applications of the coherent-dual ELDOR to molecular electron spin-qubit systems are also discussed, emphasising designing the molecular two electron-qubit systems appropriate for QC/QIP. g- and/or hyperfine A-tensor engineering approaches give us the two-and multi-electron-qubit systems, which have been a materials challenge to implement matter spin-qubit based QC/QIP. The targeted matter spin-qubits can be used to facilitate selective resonant microwave excitations achieved by the pulsed ELDOR technique. In addition to DiVincenzo's five criteria, general requisites for scalable electron spin-qubit systems as 1D periodic robust spin structures are described. According to the requisites, double- or triple-stranded helicates embedding open-shell metal cations are proposed instead of organic molecular spin-qubits.

DOI： 10.1039/b819556k

Publishing type：Research paper (scientific journal)  

Quantum computers and quantum information processing systems (QCs/QIPSs) have been the focus of emerging science and technology. Efforts to build up true QCs face seemingly intractable difficulties in preparing well-defined scalable quantum bits (qubits). In order to circumvent this problem, Lloyd proposed from the theoretical side "coupled spin arrays with an (ABC)<SUB>n</SUB> type of 1D periodicity". Realization of Lloyd's model has been materials challenge for chemists and material scientists. We have focused on the physical realization of Lloyd's model based on molecular electron spin-qubits. Here, we show our recent studies on oligo(imidazole)s-based triple-helicates relevant to Lloyd's model. We have determined their molecular structures and spin structures by X-ray analysis and single-crystal ESR spectroscopy, respectively, illustrating that they can afford suitable models for the Lloyd's approach to the implementation of QCs/QIPSs.

DOI： 10.11494/kisoyuki.2009.0.82.0

CiNii Article

Publishing type：Research paper (scientific journal)  

We have demonstrated the features of curve-structured phenalenyl chemistry, for the first time. A phenalenyl-fused corannulene anion has been designed by the annelation of a six-memberd ring across peri-positions of corannulene and generated as a stable species in a degassed solution. The (1)H and (13)C NMR spectra have shown the highly symmetrical structure and high-field shifts of protons and carbons at the asterisked positions in the chemical structure, indicating the occurrence of large negative charge densities at these positions. These results well agree with the HOMO picture and the electrostatic potential surface, demonstrating the phenalenyl anion-type electronic structure is retained in the curved-surface Pi-system. The calculated bowl-inversion barrier of the anion (11.3 kcal/mol) is larger than that of corannulene (9.2 kcal/mol) because of peri-annelation of the corannulene skeleton. The calculations of the barriers of the neutral radical (12.6 kcal/mol), radical dianion (8.1 kcal/mol), and trianion (5.4 kcal/mol) of the phenalenyl-fused corannulene have exhibited a stepwise flattening of the curvature with increase in negative charge. Therefore, we have revealed that the bowl-inversion barrier of the anion is governed by the setoff of the peri-annelation and negative charge effects.

DOI： 10.1021/ja806708j

PubMed

CiNii Article

J-GLOBAL

Publishing type：Research paper (scientific journal)  

C-60-based polyanionic high-spin clusters (S = 1-3) in their ground state have been prepared by successive chemical reductions of pristine C-60 fullerene with potassium in the presence of dicyclohexano-18-crown-6-ether in solution. Intermolecular spin-triplet, quintet, and septet states arising from the C-60-based polyanionic molecular clusters have been generated at ambient temperature and identified by CW-ESR and pulse-ESR-based two-dimensional (2D) electron spin transient nutation (2D-ESTN) spectroscopy in organic rigid glasses, for the first time. Intermolecular exchange interactions between mono- and polyanionic C-60 fullerenes are ferromagnetic via bridging potassium metal cations. The molecular structures of the polyanionic high-spin C-60 clusters in solution have been proposed by a well-established phenomenological spin Hamiltonian approach in terms of the D-tensor-based calculations for the high-spin clusters. The findings of the C-60-based high-spin molecular clusters evidence the occurrence of an intramolecular triplet C-60 dianion in the ground state. Unequivocal spin identification for molecular high-spin entities by 2D-ESTN spectroscopy and its powerfulness have been illustrated, emphasizing that the 2D-ESTN spectroscopy is useful for mixtures of molecular species with different spin multiplicities, characterized by a small g-anisotropy, for which the powerfulness of advanced high-frequency ESR spectroscopy is hampered. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ica.2008.03.048

Publishing type：Research paper (scientific journal)  

An electrochemical study of kinetically stabilized silabenzene, 1-{2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}silabenzene (1), revealed that its reduction potential is -2.96 V (vs Cp2Fe/Cp2Fe+), which is lower than that of naphthalene. The anion radical species of 1 was generated by one-electron reduction using lithium naphthalenide and characterized by ESR spectroscopy.

DOI： 10.1021/om701060a

Publishing type：Research paper (scientific journal)  

Transition-metal complexes and organic radical molecules can be used to make electric conductors and ferromagnets(1-3), the optical properties of which can be controlled by changing temperature and are used as molecular switches and sensors(4-8). Whereas a number of organic radicals in solution show temperature-dependent optical properties(5,6,9-12), such behaviour in crystalline forms is more rare(13-15). Here, we show a fully reversible continuous thermochromism with a unique mechanism in purely organic crystals of diazaphenalenyl radical. This behaviour is based on changes in the diazaphenalenyl dimers coexisting in the crystal. From the X-ray crystal structure analyses and temperature-dependent visible spectra, we conclude the presence of a thermal equilibrium between sigma-bonded and pi-bonded dimers, which are separated by 2.62(6) kcal mol(-1). This conclusion is supported by room-temperature electron spin resonance spectra of the solid, which showed signals that are attributable to a thermally accessible triplet state of the pi-dimer structure. This proves the coexistence of two dimers of different bonding natures in the crystal, causing it to demonstrate thermometer-like behaviour.

DOI： 10.1038/nmat2067

PubMed

J-GLOBAL

Publishing type：Research paper (scientific journal)  

For the purpose of syntheses of novel stable neutral radicals and generation of unique properties, we have designed and synthesized various neutral radicals based on the phenalenyl system. Recently, we have designed a highly symmetrical neutral diradical based on phenalenyl skeleton, and challenged its synthesis. We have succeeded in the synthesis of the radical precursor by the regioselective introduction of an oxygen atom into the phenalenone skeleton. In this presentation, we discuss structures and dynamic behaviors of a compound prepared by oxidation of the precursor.

DOI： 10.11494/kisoyuki.2008.0.379.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Radical-substituted radical cations are attractive species as spin-building blocks of molecular magnets or spin-electronic devices. In spite of considerable effort, there has been no report of ferri- or ferromagnets based on the methodology of radical-substituted radical cations. We report the first ferrimagnet using nitronyl nitroxide substituted dihydrophenazine radical cation tetrabromoferrate salt (NNDPP··+FeBr4-), which consists of unique three heterospins, nitronyl nitroxide, dihydrophenazine radical ion, and Fe(III) spins.

DOI： 10.11494/kisoyuki.2008.0.381.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Quantum computing/quantum information processing (QC/QIP) has been the focus of the contemporary issues in quantum science and related fields. In this study, in order to implement ensemble molecular electron-spin based QC/QIP, we have designed and synthesized a novel hetero spin biradical derivative 1 with nonequivalent g factors to demonstrate quantum operations of molecular electron-spin qubits by using pulsed Coherent-Dual ELectron-electron DOuble Resonance (CD-ELDOR) techniques in solution. In this hetero biradical 1, nitroxide radical and phenoxyl radical moieties are united by covalence bonds to truncate the intramolecular exchange interaction between the spin sites. The solution CW-ESR measurements of 1 indicated that the magnitude of the intramolecular exchange interaction is not greater than N nuclear hyperfine interactions, showing that the microwave selective excitation of an individual electron-spin qubit of 1 is feasible for solution CD-ELDOR based QC/QIP experiments.

DOI： 10.11494/kisoyuki.2008.0.277.0

CiNii Article

Publishing type：Research paper (scientific journal)  

For the implementation of molecule-based electron-spin quantum computing/quantum information processing (QC/QIP), weakened exchange-coupling between the electrons in organic biradicals with nonequivalent g-tensors at the radical sites is essential. However, stable biradicals reported so far possess too strong exchange interactions to manipulate electron-qubits for QC/QIP, because they were purposely synthesized according to the molecular design criteria for molecule-based magnetism. For controlling exchange interactions and g-engineering, we have designed novel organic biradicals by utilizing bisdurene, which possesses a perpendicular pi-conjugation, as a bridge between radical moieties. Quantum chemical calculations demonstrate the perpendicular conformation of the pi-plane and the two radical moieties, indicating the occurrence of extremely weak exchange interaction and nonequivalent g-tensors at the two radical sites. In this presentation, we will report the synthetic study of these novel biradicals and the single-crystal ESR spectral simulations based on theoretical calculations. The simulation gives a testing ground for QC/QIP experimental setups.

DOI： 10.11494/kisoyuki.2008.0.276.0

CiNii Article

Publishing type：Research paper (scientific journal)  

For the development of new functional materials such as molecule-based magnetic materials or organic conductors, many researches on stable neutral open-shell organic molecules are widely performed from the viewpoint of synthetic and physical aspects. We designed and synthesized stable neutral radicals based on phenalenyl system possessing an extensively spin-delocalized nature. Trioxotriangulene (TOT) is a 25-pi polycyclic planar neutral radical and stable enough to handle in air at room temperature. We revealed the molecular structure and the electric spin structure in terms of the X-ray analysis and ESR studies. Furthermore, we succeeded in the application to the molecular crystalline secondary battery by taking advantage of the four-stages redox ability. As a further investigation, substituent effects on both stability and redox nature by introducing substituent groups into TOT skeleton are intriguing from theoretical and experimental viewpoint. We have designed a new TOT derivative having three methoxy groups. In this presentation, we will report the synthetic study and consideration on the electric spin structure by both ESR studies and quantum chemical calculations.

DOI： 10.11494/kisoyuki.2008.0.184.0

CiNii Article

Publishing type：Research paper (scientific journal)  

We have designed an extended trimethylenemethane (TMM) biradical derivative <B>1</B>, in which pyridyl ring is inserted into each C-C bond of TMM. For kinetic stabilization phenyl groups are introduced at 2,6-positions of pyridyl rings at which relatively large spin density is predicted. Dication <B>2</B>, the precursor of biradical <B>1</B>, was synthesized from benzoylacetone in seven steps. Upon cyclic voltammetry in acetonitrile dication <B>2</B> showed two reversible two-electron reduction waves as well as a reversible one-electron oxidation wave. This result suggested that biradical <B>1</B> would be stable on a time-scale of cyclic voltammetry. Alkali metal reduction of dication <B>2</B> was carried out with 3% Na-Hg in degassed acetonitrile-2-methyltetrahydrofuran. Four stage reduction behavior of dication <B>2</B> was appreciated by absorption spectroscopy. This result suggested that the reduction of dication <B>2</B> eventually afforded the corresponding dianion species, obtained by the four-electron reduction of dication <B>2</B>. ESR spectrum of biradical <B>1</B> in the solid state at 77 K did not give typical signals due to triplet species but an unstructured broad signal because of the contamination of doublet species. Therefore, we measured spin nutation spectra of biradical <B>1</B> and could confirm the generation of biradical <B>1</B> as triplet species.

DOI： 10.11494/kisoyuki.2008.0.182.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Synthesis and elucidations of molecular and electronic-spin structures of novel stable neutral radical derivatives are fundamentally important issues for the development of spin-mediated molecular functional materials. Oxophenalenoxyl derivatives are persistent neutral radicals with two oxygen-atoms in the phenalenyl skeleton. Importantly, electronic-spin structures of these neutral radicals are intrinsically different in the topological symmetry from that of the phenalenyl. As the two-dimensional pi-extended derivative of 6-oxophenalenoxyls, recently we synthesized and isolated trioxotriangulene neutral radical derivative having <I>C</I><SUB>3</SUB>-symmetric and 25pi-conjugated molecular/electronic structures. In this work, we have evaluated the redox ability and electronic-spin structure of this neutral radical by CV and ESR measurements, and DFT calculations.

DOI： 10.11494/kisoyuki.2008.0.183.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Radical-substituted radical cations are attractive compounds as spin building blocks of molecule-based magnets. We now report syntheses and magnetic behaviors of <B>NN-TOT</B><SUP>•+</SUP>MX<SUB>4</SUB><SUP>-</SUP> (M = Fe, Ga; X = Cl, Br). <B>NN-TOT</B><SUP>•+</SUP>MX<SUB>4</SUB><SUP>-</SUP> was synthesized by chemical oxidation of neutral <B>NN-TOT</B>. <B>NN-TOT</B><SUP>•+</SUP>FeCl<SUB>4</SUB><SUP>-</SUP> showed a magnetic phase transition at 3 K with a magnetic hysteresis, whereas <B>NN-TOT</B><SUP>•+</SUP>FeBr<SUB>4</SUB><SUP>-</SUP> showed a magnetic phase transition at 4 K without a magnetic hysteresis. These results suggest that <B>NN-TOT</B><SUP>•+</SUP>FeCl<SUB>4</SUB><SUP>-</SUP> and <B>NN-TOT</B><SUP>•+</SUP>FeBr<SUB>4</SUB><SUP>-</SUP> are transformed into a ferrimagnet and a meta magnet, respectively. Detailed studies for all compounds will be discussed.

DOI： 10.11494/kisoyuki.2008.0.278.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Design and synthesis of novel stable organic open-shell molecules are important issues in the molecule-based magnetism. We study stable neutral radicals based on phenalenyl system. Among them, 6-oxophenalenoxyl is an air-stable neutral radical and possesses an extensively spin-delocalized features and a high electron-accepting ability. By taking advantage of these natures, we synthesized a 6-oxophenalenoxyl linked with tetrathiafulvalene (TTF), showing spin-center transfer depending on solvent or temperature and solvato-/thermochromism.<BR> We have newly designed and synthesized 6-oxophenalenoxyl incorporated with 1,6-dithiapyrene we originally synthesized as an electron-donor molecucle possessing an extensive π-conjugation and a high redox ability similar to TTF. This system also shows spin-center transfer and solvato-/thermochromism phenomena. In this presentation, we report these phenomena and the spin structures of this system before/after spin-center transfer determined by ENDOR/TRIPLE spectroscopies.

DOI： 10.11494/kisoyuki.2008.0.185.0

CiNii Article

Publishing type：Research paper (scientific journal)  

We have studied on electronic and magnetic properties of radical-substituted radical cations. Pyrene structure has unique electronic properties; the HOMO and LUMO of pyrene has a nodal plane passing through C2 and C7 atoms. For the developments of new stable high spin species of diradical dication, we have designed and synthesized a 1,3-bis(dialkylamino)pyrene derivative linked with dihydrophenazine moiety on C7 atom. In the ESR spectrum of the diradical dication species, we have observed the allowed and forbidden signals derived from triplet state. In this presentation, we discuss the synthetic method and the electronic structure of the diradical dication.

DOI： 10.11494/kisoyuki.2008.0.181.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Trioxytriphenylamine (TOT) radical cations are stable species with planar triphenylamine structure. We have recently shown that TOT•FeBr4 salt shows a phase transition into an antiferromagnet at TN ~ 7 K. In order to increase the dimension of magnetic interactions, we have designed and synthesized calcogen-atom-introduced TOT. Tri-(methylthio)-substituted TOT radical cation tetrabromoferrate salts was found to exhibit a phase transition into a meta-magnet around 5 K. The detailed crystal structures and properties of this and related calcogen-atom-introduced TOT radical cation salts will be presented.

DOI： 10.11494/kisoyuki.2008.0.180.0

CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.200705583

PubMed

CiNii Article

J-GLOBAL

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.200704752

PubMed

CiNii Article

J-GLOBAL

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Pulsed electron nuclear double resonance (ENDOR) spin technology has been invoked for realization of a quantum computer (QC). Sample preparation of molecular spins, quantum operations, and measurements have been performed successfully, showing that ENDOR QC is feasible. We have employed a typical stable organic open-shell entity, malonyl radical, for pulsed ENDOR-based QC experiments. Time proportional phase incrementation (TPPI) technique was applied in order to characterize entangled states. The appearance of the entanglement between electron and nuclear spins was discussed based on the pulsed ENDOR-QC experiments with the TPPI detection. The generated entangled state was operated by both the microwave and RF pulses, demonstrating the appearance of a spinor property with four-pi periodicity due to electron spin-1/2, in a straightforward manner for the first time. Interconversion from one entangled state to the other one via quantum operation was demonstrated. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2007.06.031

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

The tetrachloroferrates of the 2,2':6',2 '':6 '',6-trioxytriphenylamine (TOT center dot+center dot FeCl4-) and 2,2':6',2 ''-dioxytriphenylamine (DOT center dot+center dot FeCl4-) radical cations were prepared, and their structures, magnetic properties, and the relationship between them were investigated. The TOT center dot+ moiety had a highly planar structure and packed as a dimer surrounded by tetrachroferrates, which also formed a dimer structure. The magnetic properties of TOT center dot+center dot FeCl4- were characterized by strong (2J/k(B) = similar to -1.3 x 10(3) K, H = -2JS(1/2)center dot S-1/2) and weak (2J/k(B) = -1.76 K, H = -2JS(5/2)center dot S-5/2) antiferromagnetic interactions due to the (TOT center dot+)(2) and (FeCl4-)(2) structures, respectively. DOT center dot+ had a twisted form and no dimer formation was observed between the DOT center dot+'s and FeCl4-'S. Instead, short contacts between the DOT center dot+ and chlorine atoms and between the DOT center dot+'s producing a DOT center dot+ chain were observed. The magnetic properties of DOT center dot+center dot FeCl4- were characterized by a 3D magnetic phase transition to an antiferromagnet with T-N = similar to 8 K.

DOI： 10.1021/ic7012649

PubMed

CiNii Article

J-GLOBAL

Publishing type：Research paper (scientific journal)  

3-Oxophenalenoxyl derivatives, neutral pi-radicals having two oxygen atoms at 1,3-position on a phenalenyl skeleton, possess most of their spin densities at the two oxygen atoms and the 2-position, featuring in easy dimerization at the 2-position. For the decrease in spin density at the 2-position by invoking spin-delocalization into the 2-substituted p-systems, we have designed 2-thienyl-3-hydroxyphenalenone derivatives as synthetic precursors of neutral p-radicals, and conducted their oxidation reactions by using a variety of oxidants. The chemical structures of the dimer obtained were unambiguously determined by FABMS, IR, and NMR spectra with help of density functional theory calculations, showing the formation of the bonds on the thienyl moieties. These observations and DFT calculations illustrate the occurrence of a considerable amount of spin-delocalization into the 2-substituted-thienyl moieties from the 3-oxophenalenoxyl skeletons. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2007.05.018

Publishing type：Research paper (scientific journal)  

A polyalkylated triamine, 2,2,4,4 '-tetrabromo-4 ''-methyl-5,5 '-bis(di(3,4-di-methylphenyl)amino)triphenylamine, was designed and successfully synthesized as a model precursor for purely organic cationic high-spin systems. Cyclic voltammetry measurement revealed that the triamine gives stable mono- and dicationic states and fairly unstable tricationic state. Novel electron transfer stopped-flow (ETSF) methods were invoked for characterizing the absorption spectra of the corresponding mono- and oligo-cationic states. The triplet state of the dication was confirmed by ESR spectroscopy. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2006.09.057

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

As a novel crystal engineering approach to organic molecule-based magnets, we have proposed a strategy of bio-inspired molecular assemblage based on intermolecular hydrogen bonding. Complementary hydrogen bonding between nucleobases as found in DNA is a promising non-covalent interaction for controlling the molecular arrangement of open-shell building block molecules. The hydrogen bonding of complementary nucleobases substituted with radical entities of different spin quantum numbers S, e.g., S = 1 and S = 1/2, gives rise to a heteromolecular aggregation of the S = 1 and S = 1/2 entities, leading to organic ferrimagnetics. In this study, we have designed and synthesized a thymine-substituted nitronyl nitroxide biradical (1) as a triplet (S = 1) component for the bio-inspired ferrimagnetic system. The molecular ground state of 1 has been found to be triplet (S = 1) with a singlet-triplet energy gap of 2J/k(B) = 21.4 K from magnetic susceptibility measurements. It has been found from X-ray structure analyses that the molecules form hydrogen-bonded aggregates in the crystalline solid state, in which the thymine moiety plays a primary role in the molecular packing. The ground-state triplet biradical serves as an S = 1 building block for bio-inspired molecule-based magnets with hydrogen-bonded nucleobase pairings. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2006.10.044

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A ligand, 4-methoxy-4 ',4 ''-bis[N,N-bis(2-pyridylmethyl) aminomethyl]triphenyl-amine, and its palladium and copper dinuclear complexes were designed and prepared in order to examine intramolecular interactions between an organic cation radical and the metal ion. Novel NMR techniques, COSY and NOESY, were applied to the palladium complex to examine its conformation in solution. The palladium complex was found to prefer a folded conformation at ambient temperature, indicating the occurrence of intramolecular stacking interaction. CV measurements of the copper complex showed reversible Cu-I/Cu-II and TPA/TPA(+) redox couples. The spin-spin interaction in the radical pendant copper complex generated upon one electron oxidation of the copper complex was examined by cw-ESR measurements. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2006.10.031

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A stable cationic biradical has been designed and synthesized, and its magnetic property and crystal structure have been examined. An iminonitroxide derivative of 3,5-disubstituted pyridine (1) with a triplet ground state has been cationized by a reaction with methyl trifluoromethanesulfonate (MeTfO), which gave a salt of N-methylated pyridinium 2(+), 2(+) . TfO-. The ground state of the cation 2+ has been found to be triplet with 2J/k(B) = 7.5 K from magnetic susceptibility measurements for 2(+) . TfO- in a magnetically diluted organic matrix. The magnetic susceptibility of neat crystalline solids of 2(+) . TfO- has been explained by an exchange coupling model based on the X-ray crystal structure. It is well known that the energy preference for a high-spin ground state for a m-phenylene coupling unit is disturbed by heteroatomic substitution and an ionic charge. The present experimental results show that the high-spin preference in I is little affected by the ionic charge in 2(+). The ground-state triplet biradical serves as building blocks for molecule-based magnets of S &gt; 1/2 of molecular assemblages based on electrostatic interactions between molecular ions. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2006.09.032

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A novel bis(imino nitroxide)-substituted resorcinol 3H, that has two metal-binding sites with two pairs of the phenolate anion and the imino nitrogen atom, was prepared. The powdered sample of 3H showed an intramolecular ferromagnetic interaction (J/k(B) +5 K) between two (imino nitroxide)s through a m-phenylene bridge and a weak intermolecular antiferromagnetic interaction (J/k(B) = 0.9 K). The reaction of 3H with copper acetate in methanolic ammonia was examined to give a hardly soluble Cu-complex that exhibited ferromagnetic behavior in relatively high temperatures (298-55 K). (c) 2006 Published by Elsevier Ltd.

DOI： 10.1016/j.poly.2006.09.058

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

We have designed and synthesized new biradicals of p-phenylene-bis(nitronyl nitroxide) substituted with two methoxy groups at 2,3- (2) and 2,5-positions (3). A parent biradical p-phenylene-bis(nitronyl nitroxide) (1) has intramolecular antiferromagnetic exchange interaction of 2J/k(B) = -104 K similar to -106 K with a torsion angle of 28.5 degrees between the phenyl and the imidazole rings of nitronyl nitroxide. X-ray crystal structure analysis shows that the bulky substituents in 2 and 3 give large torsion,angles of 65-70 degrees. The larger torsion angles should weaken the magnitude of intramolecular exchange interactions, which is attributed to a decrease in R-conjugation over the p-phenylene and the radical groups. Magnetic susceptibility measurements indicate that the intramolecular exchange interactions in 2 and 3 are severely weakened to about 6% of that in 1, 2J/k(B) = -6 K similar to -8 K. The relation between the torsion angle and the intramolecular exchange interaction is consistent with DFT calculations. The ground-state singlet biradicals with suppressed intramolecular exchange interactions can be a building block for exotic exchange-coupled spin systems as predicted in our theoretical studies. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2006.09.034

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A tetraaryl-m-phenylenediamine dication diradical in the triplet ground state was chemically generated and decomposed in preparative scale. The obtained mixture was separated and purified to examine the decomposed products. A nitro compound and a biaryl were formed as the main products, indicating the cleavage of the pi-conjugation. The relationship between the substituent influence and the structure of the decomposed products, and reaction mechanism are reported. These results serve for establishing guidelines for molecular designing of next-generation charged high-spin molecular systems such as oligoarylamine-based pluri-charged high-spin molecules, in a more sophisticated manner. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2006.09.059

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A cytosine-substituted nitronyl nitroxide monoradical 1 and a biradical 2 with a singlet (S = 0) ground state have been synthesized and characterized as building blocks for organic molecule-based magnets. X-ray crystallographic analyses have shown that the molecular packing of I features in intermolecular hydrogen bonding of the cytosine moiety, giving a spin ladder chain structure based on nitronyl nitroxide radical moieties. For the biradical 2, the magnetic susceptibility suggests the singlet ground state with the intramolecular antiferromagnetic exchange interaction of J/k(B) similar to - 5 K. These radicals can be components for Watson-Crick base pairing, leading to hydrogen-bonded heteromolecular assembly such as bio-inspired molecule-based ferrimagnets. (c) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2007.01.004

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

As a novel molecular design for genuinely organic molecule-based ferrimagnets, we have proposed a strategy of "single-component organic molecule-based ferrimagnetics". In this study, we have designed and synthesized a triradical p-trisNN (1) as a building block for single-component ferrimagnetics, in which a m-phenylene-based pi-biradical and a pi-monoradical are connected in a benzyl-phenyl ether framework. The triradical retains the magnetic degrees of freedom for both S = 1 and S = 1/2 spins in the single molecule. X-ray crystallographic analyses show that 1 has a head-to-tail packing with an approximately isosceles triangular geometry, which is favorable for a ferrimagnetic spin alignment. From the analysis of crystal and magnetic susceptibility measurements, the triradical is found to form exchange-coupled systems composed of six S = 1/2 spins in the repeating unit of the crystalline solid state. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2006.09.035

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A stable guanine-substituted nitronyl nitroxide radical 1 has been synthesized and characterized. The single-crystal structure analyses and magnetic susceptibility measurements exhibit a one-dimensional architecture of guanine base resulting from carbonyl-amino hydrogen bonds in the solid state, giving a 1D ferromagnetic chain of the radical moieties.

DOI： 10.1039/b702606d

PubMed

CiNii Article

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A new Kekule polycyclic hydrocarbon with a singlet biradical index of 50% was synthesized. The singlet biradical character was assessed with UV and H-1-NMR spectroscopy, cyclic voltammetry, SQUID magnetic susceptibility measurement, and quantum chemical calculations.

DOI： 10.1021/ol062604z

PubMed

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A bio-inspired motif of hydrogen-bonded nucleobases is introduced to stable organic biradical crystals. We have synthesized a hydrogen-bonded complex based on both a cytosine-substituted nitronyl nitroxide biradical ( 1) and a closed-shell alkyl-substituted guanine ( 2). From single-crystal X-ray structure analyses, the cytosine and guanine moieties are found to form a Watson Crick pair with threefold hydrogen bonds. Magnetic susceptibility measurements reveal that the cytosine-substituted biradical 1 has a triplet ( S = 1) ground state with a singlet-triplet energy gap of 2J/k(B) = 27.0 K. This complex is the first example of Watson-Crick type base pair possessing stable high-spin organic radical moieties, which is fully characterized by single-crystal X-ray structure analysis. A face-to-face overlapping is found between the planar nucleobases, while side-by-side hydrogen bonds are found between the Watson-Crick pairs. Thus, the introduction of the radical substituent into the nucleobase results in little disturbance to the molecular arrangement usually found in nucleobase molecules: the ground-state spin multiplicity of biradical 1 is maintained.

DOI： 10.1039/b706521n

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

Stable radicals with spherical or curved-surface pi-spin networks have drawn much attention in fullerene chemistry and molecule-based magnetism, because their intra- and intermolecular interactions are intrinsically three dimensional. Corannulene is the most notable fragment of fullerenes, possessing a bowl-shaped fused-polycyclic non-alternant pi-conjugated system. Recently, we have successfully synthesized and isolated neutral radical-linked corannulene derivatives, and elucidated their electronic spin structures. In this study, to evaluate the intramolecular spin-spin interaction within the curved pi-conjugated system, we have synthesized and isolated corannulene with two phenoxyl radical moieties. Detailed physical properteis will be discussed.

DOI： 10.11494/kisoyuki.37.0.187.0

CiNii Article

Publishing type：Research paper (scientific journal)  

A triamine, 2,2',4,4'-tetrabromo-3", 4"-dimethyl-5,5'-Bis(di(3,4-dimethyl-phenyl)amino)-triphenylamine, was designed and successfully synthesized as a model precursor for purely organic cationic high-spin systems. Cyclic voltammetry measurement revealed that the triamine gives stable mono-, di-, and tricationic states at ambient temperature. Novel electron transfer stopped-flow (ETSF) methods were invoked for characterizing the absorption spectra of the corresponding mono- and oligo-cationic states. A triamine with a methoxy group on the central ring will also be reported.

DOI： 10.11494/kisoyuki.37.0.189.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Design and synthesis of novel stable organic open-shell molecules are important issues in molecule-based magnetism.6-Oxophenalenoxyl (6OP) neutral radicals were first designed and synthesized by our hands with high stabilities in air, possessing extensively spin-delocalized natures and high redox abilities. Recently, we synthesized a 6OP derivative linked with TTF as a typical electron-donor molecule. This system showed spin-center transfer and solvato-/thermochromism phenomena controllable by solvent environment and temperature. For control of both spin structure and intermolecular spin-spin interaction by hydrogen bonding effect, we have newly designed a neutral radical possessing hydrogen-bonding sites based on 6OP. In this work, we have successfully synthesized 6OP linked with <I>N</I>-butyluracil as a substituent with hydrogen-bonding sites. We discuss the synthesis and the spin structure determined in terms of ESR/ENDOR/TRIPLE measurements.

DOI： 10.11494/kisoyuki.37.0.186.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Radical-substituted radical cations are attractive spin-building blocks of magnetic materials. We report synthesis and magnetic properties of nitronyl nitroxide substituted 9,10-diphenyldihydrophenazine radical cation, NNDP<SUP>+</SUP>, FeX<SUB>4</SUB><SUP>-</SUP> (S = 5/2) and GaX<SUB>4</SUB><SUP>-</SUP> (S = 0) salts. We have also examined verdazyl-substituted analogues VzDPMX<SUB>4</SUB>. The crystal structure of NNDP-MX<SUB>4</SUB> salts (M = Fe and Ga, X = Cl and Br) showed alternate stacks consisting of NNDP<SUP>+</SUP> and FeX<SUB>4</SUB><SUP>-</SUP>. For the X = Cl salts, the short contacts between nitroxide oxygen atoms belonging to the adjacent columns were observed. For the X = Br salt, the distance between the nitroxide oxygen atoms was found to be considerable long. The verdazyl salts showed a different crystal packing structure.

DOI： 10.11494/kisoyuki.37.0.188.0

CiNii Article

Publishing type：Research paper (scientific journal)  

For realization of molecule-based magnetic materials, it is crucially important to synthesize novel stable radicals with exotic molecular skeletons and electronic structures, and to control an arrangement of radicals in the solid state. We recently synthesized and isolated bowl-shaped stable neutral radicals based on corannulene known as a hydrocarbon with a curved pi-conjugation network, and revealed their spin structures experimentally and theoretically. In this work, we have for the first time designed and isolated a novel corannulene derivatives possessing semiquinone radical substructure which provide the possibility of multi-dimensionally intermolecular spin-spin interactions by a chelation with metal ions and pi-pi interactions. We have revealed their electronic spin structures based on hyperfine coupling constants of protons on corannulene moieties and counter cations determined in terms of ESR/ENDOR/TRIPLE studies.

DOI： 10.11494/kisoyuki.37.0.185.0

CiNii Article

Publishing type：Research paper (scientific journal)  

The reaction between an imidazole-functionalized EDT-TTF and F(4)TCNQ produced a zwitterionic pi-radical, which formed a self-assembled structure by the cooperation of hydrogenbonds and multiple S. S interactions and exhibited three-step oxidation processes and a high electrical conductivity as a single-component organic molecule.

DOI： 10.1039/b707113b

PubMed

CiNii Article

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A new one-dimensional chain complex, Mn(hfac)(2)-bridged [2-(3-pyridyl)(nitronyl nitroxide) Mn(hfac)(2)](2), was prepared and its structure and magnetic properties were elucidated; the complex exhibited a large antiferromagnetic interaction of J(1)=-185 K between the three Mn(II) atoms and the two nitronyl nitroxides to give S=13/2 spin units and a small ferromagnetic interaction of J(3)'=+0.02 K between these spin units at low temperatures (50-1.9 K), compatible with the theoretical analysis for model compounds.

DOI： 10.1039/b618682c

PubMed

CiNii Article

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

Radical-substituted radical cations with strong intramolecular ferromagnetic interactions are attractive compounds as spin building blocks of magnetic materials. We now report syntheses and magnetic behaviors of <B>TOT</B><SUP>·+</SUP>, <B>TOTNN</B><SUP>·+</SUP> and <B>TOTIN</B><SUP>·+</SUP> with the magnetic- (FeCl<SUB>4</SUB><SUP>-</SUP>, FeBr<SUB>4</SUB><SUP>-</SUP>) or non-magnetic (GaCl<SUB>4</SUB><SUP>-</SUP>, GaBr<SUB>4</SUB><SUP>-</SUP>) anions. <B>TOTMX<SUB>4</SUB></B> (M = Ga, Fe; X = Cl, Br) were synthesized by chemical oxidation of <B>TOT</B> using thianthrene radical cations with the corresponding counter anions. <B>TOTFeBr<SUB>4</SUB></B> and <B>TOTNNFeCl<SUB>4</SUB></B> showed interesting magnetic behaviors at low temperature. Detailed studies are in progress.

DOI： 10.11494/kisoyuki.37.0.11.0

CiNii Article

Publishing type：Research paper (scientific journal)  

The redox behavior of kinetically stabilized dipnictenes, BbtE=EBbt [E = P, Sb, Bi; Bbt = 2,6-bis[ bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl], was systematically disclosed using cyclic voltammetry and theoretical calculations. It was found that they showed reversible one-electron redox couples in the reduction region. The anion radical species of the Bbt-substituted diphosphene and distibene were successfully synthesized by the reduction of the corresponding neutral dipnictenes (BbtP=PBbt and BbtSb= SbBbt). Their structures were reasonably characterized by ESR, UV-vis, and Raman spectroscopy, and the distibene anion radical was structurally characterized by X-ray crystallographic analysis.

DOI： 10.1021/ja064062m

PubMed

J-GLOBAL

DOI： 10.1002/ange.200600553

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/cg0600602

Publishing type：Research paper (scientific journal)  

DOI： 10.1021/ja058387z

PubMed

CiNii Article

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

The authors have previously proposed a theoretical model for exotic spin alignment in organic molecular assemblages: The alternating chain of organic biradicals in a singlet (S-b = 0) ground state and monoradicals with S = 1/2 has a ferrimagnetic ground state for the whole chain, which has been termed generalized ferrimagnetism. An important feature of the generalized ferTimagnetic spin alignment has been found in the deviation of the expectation value &lt; Sb-2&gt; of the biradical spin from zero. Even a triplet-like spin state (Sb 2) = 2 (Sb = 1) has been predicted in the theoretical calculations. In this study, we have found experimental evidence for the pseudo-triplet state appearing in the ground-state singlet biradical of a real open-shell compound. At first, we have demonstrated from theoretical calculations that the singlet biradical has (Sb 2) = 2 (Sb = 1) in a molecular pair with an S = 1 metal ion as well as with the S = 1/2 monoradical. The pseudo-triplet state of the biradical affords a singlet state of the whole system of the biradical-metal ion pair, which is readily detectable in experiments for verifying the theoretical prediction. As a model compound for the biradical-metal ion pair, a transition metal complex, [(bnn)(Ni(hfac)(2))(1.5)(H2O)] (1), has been synthesized from a nitronyl nitroxide-based ground-state singlet biradical bnn and Ni(hfach). From X-ray crystallographic analyses, the compound contains a molecular pair of bnn and Ni(hfac)(2), which serves as a model system under the above theoretical studies. It has been found from the analysis of the temperature dependence of magnetic susceptibility that the bnn-Ni(hfac)(2) pair has the singlet (S = 0) ground state. The singlet ground state of the pair results from an antiparallel coupling of the pseudo-triplet of the biradical and the S = 1 spin on the Ni ion. The pseudo-triplet state in the ground-state singlet biradical has thus been verified experimentally, which is crucially important to realize the generalized ferrimagnetic spin alignment.

DOI： 10.1021/jp056052y

PubMed

CiNii Article

Publishing type：Research paper (scientific journal)  

Magnetic properties and crystal structure of a pyridine-substituted iminonitroxide biradical, 3,5-bis(4,4,5,5,-tetramethyl-4,5-dihydro-1H-imidazol-2-yl-1-oxyl)pyridine (1), were examined. The molecular ground state of 1 was found to be triplet (S = 1) with a singlet-triplet energy gap of 2J/k(B) = 7.0 K. The triplet biradical serves as a building block for molecule-based magnets of S &gt; 1/2 based on intermolecular noncovalent bonds.

DOI： 10.1007/s10909-006-9107-x

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10909-006-9099-7

Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10909-006-9173-0

Publishing type：Research paper (scientific journal)  

We report magnetic properties of novel nitronyl nitroxide triradicals, p-triNN (1) and m-triNN (2), in which a pi-conjugated biradical with a singlet ground state and a doublet monoradical are united by a-bonds of an ether bridge. Two kinds of intramolecular exchange interactions, one between the biradical and monoradical entities J(sigma) through the sigma-bonds and the other within the biradical moiety J(pi) through the pi-conjugation, were examined by paramagnetic susceptibility chi(m) for the sample dispersed in an organic polymer film. The magnitude of J(sigma) was found to be much weaker than that of J(pi). This result indicates that the triradicals 1 and 2 can be used as a building block for generalized ferrimagnets, which from our theoretical calculations have been predicted to exhibit an exotic spin alignment.

DOI： 10.1007/sI0909-006-9097-8

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.200600553

CiNii Article

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

Phenalenyl radical has an intriguing pi-electronic system, and is expected as a promising component of organic molecule-based magnets and conducting materials. Recently, we have designed, synthesized, and isolated tert-butylated phenalenyl and tert-butylated 1,3-diazaphenalenyl in the crystalline states. We have also clarified their electronic and magnetic properties, and revealed exotic heteroatomic effects on the pi-electronic system of phenalenyl. These results have encouraged us to design a sulfur-substituted phenalenyl derivative with methoxy groups for further developments of electronically-modified new phenalenyls. In this presentation, we report the synthetic methods and properties of the sulfur-substituted phenalenyl cation and its charge transfer complexes.

DOI： 10.11494/kisoyuki.18.0.121.0

CiNii Article

Publishing type：Research paper (scientific journal)  

For elucidation of electronic spin structures, and intra- and intermolecular magnetic interactions within and between pi-conjugation system(s), it is crucially important to develop novel stable neutral radicals. We have recently started to investigate stable neutral radicals linked with corannulene, a hydrocarbon with a curved pi-conjugation network, and already synthesized and isolated corannulene derivatives with some neutral radicals. And, we have revealed that the spin of phenoxyl derivative is more larger delocalized into the curved pi-surface than that of 6-oxoverdazyl and iminonitroxide derivatives. More recently, we have designed a corannulene derivative substituted with a <I>t</I>-butyl nitroxide radical moiety as a new stable neutral radical. In this work, we have successfully synthesized and isolated it. ESR/ENDOR/TRIPLE and DFT calculations revealed that the spin densities were widely spread over the curved-surface as same as those of phenoxyl derivative.

DOI： 10.11494/kisoyuki.18.0.350.0

CiNii Article

Publishing type：Research paper (scientific journal)  

For implementing new secondary batteries based on organic crystalline molecules, we have focused on open-shell molecular entities such as 6-oxophenalenoxyl neutral radical systems possessing a high stability in air and two-stage reversible redox ability. A secondary battery by the use of this molecule as a cathode active material has manifested a multi-electron chargeable ability, which is strongly correlated with the redox behavior of the molecule, realizing for the first time a molecular-crystalline secondary battery. Furthermore, we have succeeded in synthesizing a novel neutral radical with 25-pai system and its fabrication for battery. In this paper, we discuss the synthesis of neutral radicals, the fabrication of molecular crystalline secondary batteries based on these stable radicals and their properties as cathode active materials.

DOI： 10.11494/kisoyuki.18.0.83.0

CiNii Article

Publishing type：Research paper (scientific journal)  

A series of one dimensional triamine with various substituents at the central aromatic ring were designed and synthesized. Electrochemical and novel electron transfer stopped-flow (ETSF) methods were invoked for characterizing the absorption spectra of the corresponding short-lived mono- and dicationic states. Useful molecular design rules for stabilizing the di and tricationic states were elucidated.

DOI： 10.11494/kisoyuki.18.0.348.0

CiNii Article

Publishing type：Research paper (scientific journal)  

We have studied on electronic and magnetic properties of radical-substituted dihydrophenazine radical cations. When verdazyl was used as a stable radical, the radical cation were not stable. We have improved the stability of the radical cation by introducing methyl group at 7,8-position of dihydrophenazine skeleton or by using 1,5-diphenyl-6-oxoverdazyl group. The synthesis, magnetic properties, and conductivity of stable radical cation salts and related charge transfer complexes derived from the modified verdazyl-substituted dihydrophenazines are presented.

DOI： 10.11494/kisoyuki.18.0.267.0

CiNii Article

Publishing type：Research paper (scientific journal)  

To elucidate an electronic spin structure on a curved pi-conjugated system, we have recently started to investigate stable neutral radicals linked with corannulene, a partial structure of fullerene C60. We have synthesized and isolated them, and evaluated their electronic spin structures on the curved pi-surface by several spectroscopic methods and theoretical calculations. More recently, corannulene with one or two phenoxyl radical moieties were successfully synthesized and isolated as single crystals. X-ray crystal structure analyses, ESR measurements, UV measurements and theoretical calculations have revealed their molecular structures and electronic spin structures. In this presentation, we report the details of their crystal structures and physical properties.

DOI： 10.11494/kisoyuki.18.0.81.0

CiNii Article

Publishing type：Research paper (scientific journal)  

We propose a strategy of crystal-engineering for heteromolecular crystals composed of organic open-shell molecules, in which two kinds of open-shell molecular entity are co-crystallized and, at the same time, distinct molecular entities with differing spin multiplicities are adjacent to each other in a crystalline solid state. Stable organic triradicals of nitronylnitroxide and iminonitroxide based on the benzene-1,3,5-triyl framework, trisNN ( 3) and trisIN ( 4), have been designed and synthesized. These molecules consist of a m-phenylene-substituted biradical and a monoradical moiety united by an ester bridge. From X-ray crystallography, these molecules have been found to possess an approximately isosceles triangular geometry and fully head-to-tail molecular packing in three dimensions has been achieved in the crystalline solid state. Thus, the co-crystallization is attained by binding the two pi-conjugated radicals by sigma-bonds, retaining the magnetic degree of freedom for the two distinct open-shell moieties. The alternating aggregation of the heteromolecular assembly is achieved by tuning the molecular geometry of the building-block molecules, leading to the close packing of isosceles triangular molecules in the head-to-tail fashion. Local contacts of the nitroxide groups with large spin densities between the nearest-neighbor molecules give a six-spin molecular cluster on a tetrad of the bi-, mono-, mono-, and biradical moieties in the head-to-tail stacking. Temperature dependence of magnetic susceptibility of the crystalline solids of 3 and 4 has been analyzed on the basis of their crystal structures. The six-spin cluster model has reasonably explained the susceptibility.

DOI： 10.1039/b518416a

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.200502695

CiNii Article

Other URL： http://orcid.org/0000-0003-1274-7470

Publishing type：Research paper (scientific journal)  

A Watson-Crick type molecular complex of adenine and thymine bases substituted with the stable radical of nitronylnitroxide has been synthesized, which forms a double-chain spin system in the crystal.

DOI： 10.1039/b611236f

CiNii Article

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DOI： 10.1039/b609760j

Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.200603127

CiNii Article

Publishing type：Research paper (scientific journal)  

6-oxophenalenoxyl, we designed and synthesized, is a stable neutral radical possessing high electron-accepting ability similar to chloranil. Recent year, we designed and synthesized a new diad system compised of 6-oxophenalenoxyl and tetrathiafulvalene as an electron donor molecule, demonstrating spin-center transfer and solvato-/thermochromism phenomena induced by intramolecular electron transfer controllable by hydrogen-bonding nature or temperature change. In this presentation, we discuss that nature of intramolecular electron transfer in terms of temperature-/solvent dependences of redox-behavior measured by CV method and UV-vis spectroscopy.

DOI： 10.11494/kisoyuki.18.0.268.0

CiNii Article

Publishing type：Research paper (scientific journal)  

A polyalkylated triamine was designed and successfully synthesized as a model precursor for purely organic cationic high-spin systems. Cyclic voltammetry measurement revealed that the triamine gives stable mono- and dicationic states and fairly unstable tricationic state. Novel electron transfer stopped-flow (ETSF) methods were invoked for characterizing the absorption spectra of the corresponding mono- and oligo-cationic states. The triplet states of the dication was confirmed by ESR spectroscopy.

DOI： 10.11494/kisoyuki.18.0.266.0

CiNii Article

Publishing type：Research paper (scientific journal)  

Recently, we have prepared new oxygen-bridged triphenylamines. We now report syntheses, structures, and magnetic properties of FeCl<SUB>4</SUB><SUP>-</SUP> and GaCl<SUB>4</SUB><SUP>-</SUP> salts of the oxygen-bridged triphenylamines. These salts were synthesized by the oxidation of the neutral triphenylamines using thianthrenium radical cation salts (FeCl<SUB>4</SUB><SUP>-</SUP> and GaCl<SUB>4</SUB><SUP>-</SUP>) as an oxidant. From the X-ray structure analysis, the followings became apparent, 1) the structures of FeCl<SUB>4</SUB><SUP>-</SUP> and GaCl<SUB>4</SUB><SUP>-</SUP> salts were isostructural each other, 2) intermolecular short contacts were observed between the adjacent radical cations or between the radical cations and counter ions. We report the structures and magnetic properties of these salts.

DOI： 10.11494/kisoyuki.18.0.177.0

CiNii Article

Publishing type：Research paper (scientific journal)  

A ligand and its palladium and copper dinuclear complexes were designed and prepared in order to examine intramolecular interactions between an organic cation radical and the metal ion. Novel NMR techniques, COSY and NOESY, were applied to the palladium complex to examine its conformation in solution. The palladium complex was found to prefer a folded conformation at ambient temperature, indicating the occurrence of intramomecular stacking interaction. CV measurements of the copper complex showed reversible CuI/CuII and TPA/ TPA+ redox couples. The spin-spin interaction in the radical pendant copper complex generated upon one electron oxidation of the copper complex was examined by cw-ESR measurements.

DOI： 10.11494/kisoyuki.18.0.176.0

CiNii Article

Publishing type：Research paper (scientific journal)  

5,5'-(m-Phenylene)bis[(10-aryl-5,10-dihydroplienazine) dications, 3a(2+) and 3b(2+) and their p-analogues 4a(2+) and 4b(2+), were prepared, and their exchange interaction was investigated. The EPR spectra of these dications at 123 K in a butyronitrile matrix showed the population of a triplet state. The temperature dependence of the EPR signal intensity (vertical bar Delta m(s)vertical bar = 2) showed that these dications had singlet ground states with Delta E-ST/k(B) = -27 to -21 K for the m-isomer 3(2+) and with Delta E-ST/k(B) = -10 to -8 K for the p-isomer 4(2+). Theoretical calculation of the exchange interaction J for these dications at the orthogonal torsion angle geometries was carried out for 3a(2+) and 4a(2+) and for (m- and p-phenylene)bisphenothiazine dications 1(2+) and 221 using the broken-symmetry approach for the singlet states. A good correlation was observed between the calculated J and a MO-energy term in the triplet state, Delta E-TMO = vertical bar HOMO(alpha) - (HOMO - 1)(alpha)vertical bar. The calculated J values were negative in the order of 10 K for the m-dications (J/k(B) = -14.7 K for 12+, -11.5 K for 3a(2+)), but much smaller negative values were found for the p-isomers (J/k(B) = -0.9 K for 2(2+), -0.8 K for 4a2+). The smaller 1J1 values for the p-dications are qualitatively consistent with the experimental Delta E-ST (2J) values.

DOI： 10.1021/jo051791w

PubMed

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DOI： 10.1016/j.poly.2005.03.042

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DOI： 10.1016/j.poly.2005.03.028

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DOI： 10.1016/j.poly.2005.03.025

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DOI： 10.1016/j.poly.2005.03.041

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DOI： 10.1016/j.poly.2005.03.027

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DOI： 10.1016/j.poly.2005.03.109

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DOI： 10.1016/j.poly.2005.03.148

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DOI： 10.1016/j.poly.2005.03.069

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The hexaazaphenalenyl anion (HAP, 3(-)), a highly symmetric heterocyclic pi system, has been synthesized and characterized. The crystal structures of its potassium salt K+(.)3(-) and copper complex Cu(2+)center dot(NH3)(4)center dot(3(-))(2) show pi-pi stacking and radially extended hydrogen bonds as well as coordination bonds constructed by the HAP anion. These in-plane and out-of-plane strong interactions demonstrate the multiple-networking ability of the HAP anion.

DOI： 10.1021/ic051583m

PubMed

CiNii Article

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DOI： 10.1016/j.synthmet.2005.07.075

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DOI： 10.1016/j.synthmet.2005.07.076

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DOI： 10.1021/cm050558b

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A typical magnetic behavior has been studied in a genuine organic radical crystal of antiferromagnetic triangular spin units, N,N,N-Tris[p-(N-oxyl-tetra- butyamino)phenyl]amine. The magnetic susceptibility measurements indicate that a ground-state doublet is achieved within a molecule when the temperature is cooled down to about 60 K from 300 K, giving the effective spin value of each molecule at lower temperatures to be S=12. Below 60 K, the magnetic susceptibility increases ferromagnetically down to 1 K, being followed by an antiferromagnetic decrease at lower temperatures. The analyses of the magnetic field dependence of heat capacity and magnetization reveals that the intermolecular ferromagnetic and antiferromagnetic interactions are working with the respective value 2 zf Jf kB =6.0 K and 2 zaf Jaf kB =-1.35 K, which reasonably explains the observed value of the transition temperature TN (0) =0.74 K at the field H=0 T: It is suggested that organic magnets order at the temperature predicted by Rushbrooke-Wood for isotropic Heisenberg spin systems, including not only the present tri-radical system, but also to the most typical genuine organic ferromagnets of mono-radical (S=12) and biradical (S=1). A fully mapped temperature-magnetic field phase boundary is obtained to be described by a single formula TN (H) = TN (0) [1- (H Hc) a] ξ with the values TN (0) =0.735 K, Hc =1.01±0.01 T, a=2.05±0.02, and ξ=0.48+0.01, where Hc =2 Hex =2×2 zaf Jaf S g μB, without any trace of the existence of the bicritical point on it as seen in normal antiferromagnets with uniaxial anisotropy. It is discussed that the critical indices may be a=2.0 and ξ=0.5 for nonfrustrated antiferromagnets with infinitesimally small anisotropy. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.72.024435

Publishing type：Research paper (scientific journal)  

An organic molecular acid-base complex has been synthesized from pyridine-substituted biradical 2 in a triplet (S = 1) ground state and a benzoic acid derivative of monoradical 3 with S = 1/2. The two constituent molecules are bound by an OH-N hydrogen bond in a crystalline solid state. The complex has been found to exhibit an antiferromagnetic phase transition at 5 K. The complex is the first example of a hydrogen-bonded heterospin, heteromolecular complex exhibiting a magnetic phase transition in purely organic moleculebased materials.

DOI： 10.1021/jp051289f

Publishing type：Research paper (scientific journal)  

Spin alignments in heterospin chains are examined from numerical calculations of model spin Hamiltonians. The Hamiltonians of the heterospin chains mimic an open-shell molecular assemblage composed of an organic biradical in a singlet (S = 0) ground state and a doublet (S = 1/2) monoradical, which are coupled by intermolecular ferromagnetic exchange interactions. It is found from numerical calculations of the spin Hamiltonians that the spin value &2rattach; S-2&2lattach; of the ground-state singlet biradical embedded in the exchange-coupled assemblage deviates from zero and contributes to the bulk magnetization. The alternating chain is found to have two kinds of ground spin states, a high- and a low-spin state. All the spins are parallel to each other in the high-spin state, which is characterized by the spin correlation function of &2rattach; S(i)center dot S-j&2lattach; = 0.25. On the other hand, the spin alignment in the low-spin state is found to be dependent on the topology of the intermolecular exchange interactions. The energy preference of the two states depends on the relative amplitude of the exchange interactions in the chain. The intermolecular ferromagnetic couplings are competing in the ground-state singlet biradical with the intramolecular antiferromagnetic interaction. The appearance of the two kinds of ground states is attributed to a quantum spin frustration effect inherent in the triangular motif of the competing interactions. Magnetic properties of a zigzag chain complex composed of a nitronyl nitroxide biradical with a singlet ground state and Cu(hfac)(2) are examined on the basis of the theoretical calculations. The vanishing magnetic moments, or the product of susceptibility and temperature chi T, at low temperatures observed for the complex are consistent with those of the low-spin state predicted in the theoretical calculations.

DOI： 10.1021/jp0441792

CiNii Article

Publishing type：Research paper (scientific journal)  

Novel hydrogen-bonded charge-transfer salts of TCNQ with mono- and diprotonated 4,4'-biimidazolium were synthesized in order to demonstrate the high potential of the 4,4'-biimidazole system in a molecular conductor from the viewpoint of crystal engineering and electronic modulation. Crystal structure analyses of neutral 4,4'-biimidazole and TCNQ salts revealed the formation of two types of hydrogen-bonding modes of the 4,4'-biimidazole moiety depending on the protonated states. Neutral 4,4'-biimidazole possessed a linear chain mode of hydrogen-bonding to construct two-dimensional network. In the TCNQ salt of monoprotonated 4,4'-biimidazolium, the 4,4'-biimidazole moiety formed a dimer by a complementary mode of hydrogen-bonding. In contrast, the salt of diprotonated 4,4'-biimidazolium showed a double linear chain mode of hydrogen-bonding to construct a three-dimensional network. The formation of two types of hydrogen-bonding modes made the difference in the stacking patterns of TCNQ columns and in their transport properties. The TCNQ salt of diprotonated 4,4'-biimidazolium exhibited high electrical conductivity (sigma(rt) = 1.1 X 10(-1) S cm(-1)).

DOI： 10.1021/jo047768c

PubMed

CiNii Article

Publishing type：Research paper (scientific journal)  

As a novel molecular designing for genuinely organic molecule-based ferrimagnets, we have proposed a strategy of "single-component ferrimagnetics". When a pi-biradical with an S = 1 ground state and a pi-monoradical with S = 1/2 are united by a-bonds, the pi-conjugation between the biradical and the monoradical moieties should be truncated in the resultant triradical. This gives magnetic degrees of freedom for both S = 1 and 1/2 in the single molecule, serving as a building block for organic molecule-based ferrimagnets under favorable conditions (single-component ferrimagnetics). We have designed and synthesized a triradical, 3-(1"oxyl-3"-oxido-4",4",5",5"-tetramethylimidazolin-2-yl)benzoic acid 2,4-bis(1"-oxyl-3"-oxido-4",4",5",5"tetramethylimidazolin-2-yl)phenyl ester (4), as a model compound for the novel approach to genuinely organic ferrimagnets. In the triradical 4, a m-phenylene-bis(nitronyl nitroxide) biradical with a triplet (S = 1) ground state is united with a phenyl nitronyl nitroxide monoradical (S = 1/2) by an ester coupler. Solution-phase ESR spectra from 4 exhibited a complex hyperfine splitting due to N-14 and H-1 nuclei. The analysis of the hyperfine structure based on perturbation calculations has revealed that the exchange interaction within the biradical moiety is much larger than those between the biradical and the monoradical moieties and the magnetic degrees of freedom for both S = 1 and 1/2 are retained in 4. An X-ray crystal structure analysis showed that the triradical molecules are arranged in a one-dimensional molecular chain in the crystal. The magnetic susceptibility in a crystalline solid state is consistent with the crystal structure.

DOI： 10.1021/jp046092m

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DOI： 10.1002/anie.200502180

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DOI： 10.1002/anie.200502303

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DOI： 10.1007/978-94-007-4893-4_8

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DOI： 10.1007/978-94-007-4887-3_3

Scopus

DOI： 10.1007/978-94-007-4887-3_4

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