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Papers by Makoto Tadokoro

Journal of Synthetic Organic Chemistry, Japan, 2004

Manipulation of molecular crystals formed from self-organization is one of important methods to d... more Manipulation of molecular crystals formed from self-organization is one of important methods to develop the new molecular functional materials. We have been looking upon in particular mutual cohesive interactions of hydrogen bonding and metal coordination as one of useful tools to construct the preprogramming super-structures. In this study, five controlled super-structures of a one-dimensional linear chain, a zig-zag ribbon, right-handed and left-handed helices, and a two-dimensional honeycomb sheet are newly created by using the neutral metal complexes with some 2, 2 "-biimidazolate mono-anions.

Materials, Feb 26, 2021

The structural and electronic properties of interfaces composed of donor and acceptor molecules p... more The structural and electronic properties of interfaces composed of donor and acceptor molecules play important roles in the development of organic opto-electronic devices. Epitaxial growth of organic semiconductor molecules offers a possibility to control the interfacial structures and to explore precise properties at the intermolecular contacts. 5,6,11,12-tetraazanaphthacene (TANC) is an acceptor molecule with a molecular structure similar to that of pentacene, a representative donor material, and thus, good compatibility with pentacene is expected. In this study, the physicochemical properties of the molecular interface between TANC and pentacene single crystal (PnSC) substrates were analyzed by atomic force microscopy, grazing-incidence X-ray diffraction (GIXD), and photoelectron spectroscopy. GIXD revealed that TANC molecules assemble into epitaxial overlayers of the (010) oriented crystallites by aligning an axis where the side edges of the molecules face each other along the 110 direction of the PnSC. No apparent interface dipole was found, and the energy level offset between the highest occupied molecular orbitals of TANC and the PnSC was determined to be 1.75 eV, which led to a charge transfer gap width of 0.7 eV at the interface.

Physical Chemistry Chemical Physics, 2022

To produce high-efficiency organic light-emitting diodes, materials that exhibit thermally activa... more To produce high-efficiency organic light-emitting diodes, materials that exhibit thermally activated delayed fluorescence (TADF) are attracting attention as alternatives to phosphorescent materials containing heavy metallic elements. Melem, a small molecule with a heptazine backbone composed only of nitrogen, carbon, and hydrogen, is known to emit light in the near-ultraviolet region and exhibit high photoluminescence (PL) quantum yield and delayed fluorescence. However, the mechanism underlying the high PL quantum yield remains unclear. This study aimed to elucidate the mechanism of the high PL quantum yield of melem by examining its optical properties in detail. When the amount of dissolved oxygen in the melem solution was increased by bubbling oxygen through it, the PL quantum yield and emission lifetime decreased significantly, indicating that the triplet state was involved in the light-emission mechanism. Furthermore, the temperature dependence of the PL intensity of melem was investigated; the PL intensity decreased with decreasing temperature, indicating that it increases thermally. The experimental results show that melem is a TADF material that produces an extremely high PL quantum yield by upconversion from the triplet to the singlet excited state.

Journal of Nanotechnology, 2012

Anionic tris (biimidazolate) nickelate (II) ([Ni(Hbim) 3 ] -), which is a hydrogen-bonding (H-bon... more Anionic tris (biimidazolate) nickelate (II) ([Ni(Hbim) 3 ] -), which is a hydrogen-bonding (H-bonding) molecular building block, undergoes self-organization into honeycomb-sheet superstructures connected by complementary intermolecular H-bonds. The crystal obtained from the stacking of these sheets is assembled into channel frameworks, approximately 2 nm wide, that clathrate two cationic K + -crown ether derivatives organised into one-dimensional (1D) double-columnar arrays. In this study, we have shown that all five cationic guest-included crystals form nanochannel structures that clathrate the 1-D double-columnar arrays of one of the four types of K + -crown ether derivatives, one of which induces a polymorph. This is accomplished by adaptably fitting two types of anionic [Ni(Hbim) 3 ] -host arrays. One is a ΔΛ-ΔΛ-ΔΛ • • • network with H-bonded linkages alternating between the two different optical isomers of the Δ and Λ types with flexible H-bonded [Ni(Hbim) 3 ] -. The other is a ΔΔΔ-ΛΛΛ • • • network of a racemate with 1-D H-bonded arrays of the same optical isomer for each type. Thus, [Ni(Hbim) 3 ] -can assemble large cations such as K + crown-ether derivatives into double-columnar arrays by highly recognizing flexible H-bonding arrangements with two host networks of ΔΛ-ΔΛ-ΔΛ • • • and ΔΔΔ-ΛΛΛ • • • .

Materials advances, 2020

Nafion membranes are recognised as cation exchangers and excellent proton conductors. Emissive Ln... more Nafion membranes are recognised as cation exchangers and excellent proton conductors. Emissive Ln III -b-diketonate complexes, [Ln III 2 (PBA) 6 ] (Ln = Eu, Tb; HPBA = N-(2-pyridinyl)benzoylacetamide), were incorporated into a transparent Nafion film. Upon incorporation, reversible emission by the green light emitter [Tb III 2 (PBA) 6 ] and red light emitter [Eu III 2 (PBA) 6 ] could be controlled through pH adjustment. [Tb III 2 (PBA) 6 ] emitted only under acidic conditions, while [Eu III 2 (PBA) 6 ] emitted only under basic conditions. Taking advantage of Nafion's high proton conductivity brought about dynamic changes in the wavelengths emitted by the film. When an in-plane external voltage was applied to the film, red wavelength emission appeared to migrate toward the negative electrode. Owing to the proton concentration gradient induced by the electric field, emission by Eu III at 615 nm was enhanced near the positive electrode, whereas proton deficiency suppressed emission by [Tb III 2 (PBA) 6 ]. Tuneable emission in the transparent Nafion system enhances its potential for use as an energy-saving material.

Chemical Communications, 2021

Journal of Physical Chemistry B, Apr 26, 2019

Dalton Transactions, 2021

Functional metal–organic squares (MOSs) and metal–organic cubes (MOCs) are important building uni... more Functional metal–organic squares (MOSs) and metal–organic cubes (MOCs) are important building units for zeolite-like metal–organic frameworks (ZMOFs), which are required to exhibit solid-state properties, such as dielectric and magnetic properties.

Crystals, 2020

A transparent film allowing tunable multicolor emission based on a composite of an organometallic... more A transparent film allowing tunable multicolor emission based on a composite of an organometallic compound and a cation-exchange membrane has been developed, in which the cyclometallated iridium(III) complex [IrIII(4Py-ppy)3] (=tris[2-(2-pyridinyl-κN)-4-(4-pyridinyl)phenyl-κC]iridium) (1) with pH-dependent emission wavelengths has been incorporated into Nafion by cation exchange. Soaking Nafion in the solution of 1 for 24 h and exposed to buffers at pH 2, 4, and 10 resulted in maximum emission wavelengths of 587, 560, and 503 nm, respectively. The photophysical properties of 1@Nafion were also enhanced, as its maximum emission wavelength was more blue-shifted than those of 602, 564, and 503 nm in the solutions. The emission quantum yields (Φ) and lifetimes (τ) of 1@Nafion prepared under an acidic condition were up to Φ = 1.8% and τ = 0.11, 0.92 μs, which are considerably higher than the corresponding solutions of Φ = 0.5% and τ = 0.02, 0.18 μs. This is attributed to the fact that 1 ...

Chemistry Letters, 2020

A type of electron-accepting N-heteroacene which can be used as a bis-bidentate ligand, tetrapyri... more A type of electron-accepting N-heteroacene which can be used as a bis-bidentate ligand, tetrapyrido[3,2-a:2¤,3¤-c:3¤¤,2¤¤j:2¤¤¤,3¤¤¤-l] [5,6,11,12]tetraazanaphthacene (TPy-TANC), was synthesized. TPy-TANC is a pyridine-fused tetraazanaphthacene which has the potential to behave as an n-type semiconductor. TPy-TANC was determined to have a monoclinic P2 1 /n space group by single-crystal X-ray diffraction analysis. The cyclic voltammogram of [(bpy) 2 Ru II (TPy-TANC)Ru II (bpy) 2 ]-(PF 6 ) 4 (bpy = 2,2¤-bipyridine) showed a reversible four-step/ six-electron transfer in the reduction at ¹0.553 (1e ¹ , TPy-TANC), ¹1.15 (1e ¹ , TPy-TANC), ¹1.81 (2e ¹ , bpy), and ¹2.02 V (2e ¹ , bpy) (vs. Fc/Fc + ).

Chemical Communications, 2021

Materials, 2021

The structural and electronic properties of interfaces composed of donor and acceptor molecules p... more The structural and electronic properties of interfaces composed of donor and acceptor molecules play important roles in the development of organic opto-electronic devices. Epitaxial growth of organic semiconductor molecules offers a possibility to control the interfacial structures and to explore precise properties at the intermolecular contacts. 5,6,11,12-tetraazanaphthacene (TANC) is an acceptor molecule with a molecular structure similar to that of pentacene, a representative donor material, and thus, good compatibility with pentacene is expected. In this study, the physicochemical properties of the molecular interface between TANC and pentacene single crystal (PnSC) substrates were analyzed by atomic force microscopy, grazing-incidence X-ray diffraction (GIXD), and photoelectron spectroscopy. GIXD revealed that TANC molecules assemble into epitaxial overlayers of the (010) oriented crystallites by aligning an axis where the side edges of the molecules face each other along the [...

Dalton Transactions, 2019

For the cyclometallation reaction with the polyaromatic ligand to Ir(N^C) complexes, the steric b... more For the cyclometallation reaction with the polyaromatic ligand to Ir(N^C) complexes, the steric bulkiness determines whether the six-membered or five-membered N^C metallocycle is formed.

Chemistry – A European Journal, 2019

In the originally published manuscript, the name Yuki Ohata wasm isspelt as Yuki Ohhata,ane rror ... more In the originally published manuscript, the name Yuki Ohata wasm isspelt as Yuki Ohhata,ane rror that the authorsw ish to point out and correct herewith.

Scientific Reports, 2017

K3Cu3AlO2(SO4)4 is a highly one-dimensional spin-1/2 inequilateral diamond-chain antiferromagnet.... more K3Cu3AlO2(SO4)4 is a highly one-dimensional spin-1/2 inequilateral diamond-chain antiferromagnet. Spinon continuum and spin-singlet dimer excitations are observed in the inelastic neutron scattering spectra, which is in excellent agreement with a theoretical prediction: a dimer-monomer composite structure, where the dimer is caused by strong antiferromagnetic (AFM) coupling and the monomer forms an almost isolated quantum AFM chain controlling low-energy excitations. Moreover, muon spin rotation/relaxation spectroscopy shows no long-range ordering down to 90 mK, which is roughly three orders of magnitude lower than the exchange interaction of the quantum AFM chain. K3Cu3AlO2(SO4)4 is, thus, regarded as a compound that exhibits a Tomonaga-Luttinger spin liquid behavior at low temperatures close to the ground state.

Dalton Transactions, 2018

H-Bonded metal complex dimers with reversible redox behavior connected by an LBHB can provide a u... more H-Bonded metal complex dimers with reversible redox behavior connected by an LBHB can provide a unique mixed-valency state. However, the metal complexes substituted two H-bonding protons to two Ag+ions electrochemically have no mixed-valency state.

Inorganic Chemistry, 2017

A proton-coupled electron transfer (PCET) reaction was widely studied with isolated organic molec... more A proton-coupled electron transfer (PCET) reaction was widely studied with isolated organic molecules and metal complexes in solution in view of the biological catalytic reaction, while studying this reaction in the crystalline or solid-state phase, which has a novel example, would give insight into the rather internal environment of proteins without solvation and a creation of new molecular materials. We tried to crystallize a hydrogen-bonded (H-bonded) coordination polymer with one-dimensional nanoporous channels, formed from redox-active Ru III complexes, [Ru III (Hbim) 3 ] (Hbim -= 2,2′-biimidazolate monoanion). As a result, a synchronized collective PCET phenomenon was observed for the molecular nanoporous crystal by novel solid-state cyclic voltammetry (CV), which could be measured by only setting some crystals on the electrode surface. The nanoporous crystals, {[Ru III (Hbim) 3 ]} n (1), are simultaneously induced to a synchronized collective Ru II Ru III mixed-valence state, {Ru II Ru III } n , with alternating arrays of Ru II and Ru III complexes by PCET in a way of the reductive state of {Ru II Ru II } n . Further, a new crystal with {Ru II Ru III } n , {[Ru II (H 2 bim)(Hbim) 2 ][Ru III (bim) (Hbim) 2 ][K(MeOBz) 6 ]} n (2), was also prepared, and the solid-state CV revealed the same electrochemical behavior of {Ru II Ru III } n with 1. The single crystal with {Ru II Ru III } n of 2 was unusually a semiconductor with 5.12 × 10 -6 S/cm conductivity at 298 K by an impedance method (8.01 × 10 -6 S/cm by a direct-current method at 277 K). Thus, an unprecedented electron-hopping conductor driven by a lowbarrier proton transfer through a PCET mechanism (E a = 0.30 eV) was realized in the H-bonding molecular crystal with {Ru II Ru III } n . Such studies on a PCET reaction in the crystalline state is not only worthwhile as a model of essential biological reactions without solvation, but also proposed to a new design of molecular materials to occur an electron transfer by using an intermolecular H-bond.

Acta Crystallographica Section A Foundations of Crystallography, 2008

Tungsten trioxides and their alkali-metal-intercalated products MzWO3 + show potential for applic... more Tungsten trioxides and their alkali-metal-intercalated products MzWO3 + show potential for application in electrodes, as ion exchangers, catalysts and the treatment of radioactive waste. Hexagonal tungsten bronze (HTB) features hexagonal channels, of diameter ~0.54 nm, that may be useful for selective and reversible binding of metal ions. In particular doping of HTB with molybdenum (Mo-HTB) has been reported to enhance the uptake of Cs + and Sr 2+ . We have conducted a powder diffraction study, using both x-rays and neutrons on a series of MzHTB (M = Na + , Mn 2+ , Ba 2+ , Ce 3+ , Pb 2+ ), including some doped with molybdenum (Mo-HTB) synthesized using hydrothermal methods. Rietveld refinement of the diffraction patterns show that doping with Mo rapidly degrades the crystallinity of HTB by creating a high degree of disorder in the a-b planes, suggesting that the presence of Mo retards the hydrothermal crystallization process. The refinements confirm previous reports of an exchangeable metal ion binding site that displays varying degrees of affinity for the various metal ions studied. The solution binding affinity behaviour of the Mo-HTB's was also investigated for selected ions (M = Co 2+ , Gd 3+ , Ce 3+ , Ce 4+ Tl + , Pb 2+ doped with respective radiotracer) in a range of concentrations of acid and electrolytes solutions. These results show that the optimum condition for metal ion binding depends not only on the Mo doping level, but also the charge and redox chemistry of the exchange cation. In combination, the structure information and the solution chemistry indicate that the loading capacity of the each metal ion is also dependent on the microstructure of the HTB.

Inorganic chemistry, Jan 5, 2017

The judicious selection of pairs of benzimidazole-ligated ruthenium complexes allowed the constru... more The judicious selection of pairs of benzimidazole-ligated ruthenium complexes allowed the construction of a rechargeable proton-coupled electron-transfer (PCET)-type redox battery. A series of ruthenium(II) and -(III) complexes were synthesized that contain substituted benzimidazoles that engage in PCET reactions. The formation of intramolecular Ru-C cyclometalation bonds stabilized the resulting ruthenium(III) complexes, in which pKa values of the imino N-H protons on the benzimidazoles are usually lower than those for the corresponding ruthenium(II) complexes. As a proof-of-concept study for a solution redox battery based on such PCET reactions, the charging/discharging cycles of several pairs of ruthenium complexes were examined by chronopotentiometry in an H-type device with half-cells separated by a Nafion membrane in unbuffered CH3CN/H2O (1/1, v/v) containing 0.1 M NaCl. During the charging/discharging cycles, the pH value of the solution gradually changed accompanied by a cha...

Journal of Molecular Structure, 2013

We investigated the static structures and dynamic behaviors for guest molecules (CH 4 and CO 2 ) ... more We investigated the static structures and dynamic behaviors for guest molecules (CH 4 and CO 2 ) in small and large cavities which are composed of 12 pentagonal faces of 20 water molecules (5 12 ), and 12 pentagonal and 2 hexagonal faces of 24 water molecules (5 12 6 2 ), respectively, by B3LYP/6-311++G(d,p) level calculations in GAUSSIAN 09, and using quantum molecular dynamics (QMD) (NVT MD with semiempirical MO PM3 method). For the static calculations, the guest CO 2 and CH 4 molecules are around at the center of small and large cavities with weak H-bond formations of H-O-H···O 2 C and H 2 O···H 4 C van der Waals interaction systems. Calculated carbon NMR chemical shifts of the CH 4 in the gas-state and in the small and large cavities reflected the C-13 experimental tendency, while the calculated carbon NMR chemical shifts of the CO 2 in the three states almost correspond to the experimental value in the gas-state. For QMD calculations, we used a cluster model containing 73 water molecules, and examined dynamic behavior of guest molecules in the shell cluster model of 39 water molecules which own small and large cavities. The dynamic behavior of guest molecules are simulated from the trajectory distribution of molecular center of the mass due to the translational motion, and also analyzed using librational motions of guest molecules in the cavities.

Journal of Synthetic Organic Chemistry, Japan, 2004

Manipulation of molecular crystals formed from self-organization is one of important methods to d... more Manipulation of molecular crystals formed from self-organization is one of important methods to develop the new molecular functional materials. We have been looking upon in particular mutual cohesive interactions of hydrogen bonding and metal coordination as one of useful tools to construct the preprogramming super-structures. In this study, five controlled super-structures of a one-dimensional linear chain, a zig-zag ribbon, right-handed and left-handed helices, and a two-dimensional honeycomb sheet are newly created by using the neutral metal complexes with some 2, 2 "-biimidazolate mono-anions.

Materials, Feb 26, 2021

The structural and electronic properties of interfaces composed of donor and acceptor molecules p... more The structural and electronic properties of interfaces composed of donor and acceptor molecules play important roles in the development of organic opto-electronic devices. Epitaxial growth of organic semiconductor molecules offers a possibility to control the interfacial structures and to explore precise properties at the intermolecular contacts. 5,6,11,12-tetraazanaphthacene (TANC) is an acceptor molecule with a molecular structure similar to that of pentacene, a representative donor material, and thus, good compatibility with pentacene is expected. In this study, the physicochemical properties of the molecular interface between TANC and pentacene single crystal (PnSC) substrates were analyzed by atomic force microscopy, grazing-incidence X-ray diffraction (GIXD), and photoelectron spectroscopy. GIXD revealed that TANC molecules assemble into epitaxial overlayers of the (010) oriented crystallites by aligning an axis where the side edges of the molecules face each other along the 110 direction of the PnSC. No apparent interface dipole was found, and the energy level offset between the highest occupied molecular orbitals of TANC and the PnSC was determined to be 1.75 eV, which led to a charge transfer gap width of 0.7 eV at the interface.

Physical Chemistry Chemical Physics, 2022

To produce high-efficiency organic light-emitting diodes, materials that exhibit thermally activa... more To produce high-efficiency organic light-emitting diodes, materials that exhibit thermally activated delayed fluorescence (TADF) are attracting attention as alternatives to phosphorescent materials containing heavy metallic elements. Melem, a small molecule with a heptazine backbone composed only of nitrogen, carbon, and hydrogen, is known to emit light in the near-ultraviolet region and exhibit high photoluminescence (PL) quantum yield and delayed fluorescence. However, the mechanism underlying the high PL quantum yield remains unclear. This study aimed to elucidate the mechanism of the high PL quantum yield of melem by examining its optical properties in detail. When the amount of dissolved oxygen in the melem solution was increased by bubbling oxygen through it, the PL quantum yield and emission lifetime decreased significantly, indicating that the triplet state was involved in the light-emission mechanism. Furthermore, the temperature dependence of the PL intensity of melem was investigated; the PL intensity decreased with decreasing temperature, indicating that it increases thermally. The experimental results show that melem is a TADF material that produces an extremely high PL quantum yield by upconversion from the triplet to the singlet excited state.

Journal of Nanotechnology, 2012

Anionic tris (biimidazolate) nickelate (II) ([Ni(Hbim) 3 ] -), which is a hydrogen-bonding (H-bon... more Anionic tris (biimidazolate) nickelate (II) ([Ni(Hbim) 3 ] -), which is a hydrogen-bonding (H-bonding) molecular building block, undergoes self-organization into honeycomb-sheet superstructures connected by complementary intermolecular H-bonds. The crystal obtained from the stacking of these sheets is assembled into channel frameworks, approximately 2 nm wide, that clathrate two cationic K + -crown ether derivatives organised into one-dimensional (1D) double-columnar arrays. In this study, we have shown that all five cationic guest-included crystals form nanochannel structures that clathrate the 1-D double-columnar arrays of one of the four types of K + -crown ether derivatives, one of which induces a polymorph. This is accomplished by adaptably fitting two types of anionic [Ni(Hbim) 3 ] -host arrays. One is a ΔΛ-ΔΛ-ΔΛ • • • network with H-bonded linkages alternating between the two different optical isomers of the Δ and Λ types with flexible H-bonded [Ni(Hbim) 3 ] -. The other is a ΔΔΔ-ΛΛΛ • • • network of a racemate with 1-D H-bonded arrays of the same optical isomer for each type. Thus, [Ni(Hbim) 3 ] -can assemble large cations such as K + crown-ether derivatives into double-columnar arrays by highly recognizing flexible H-bonding arrangements with two host networks of ΔΛ-ΔΛ-ΔΛ • • • and ΔΔΔ-ΛΛΛ • • • .

Materials advances, 2020

Nafion membranes are recognised as cation exchangers and excellent proton conductors. Emissive Ln... more Nafion membranes are recognised as cation exchangers and excellent proton conductors. Emissive Ln III -b-diketonate complexes, [Ln III 2 (PBA) 6 ] (Ln = Eu, Tb; HPBA = N-(2-pyridinyl)benzoylacetamide), were incorporated into a transparent Nafion film. Upon incorporation, reversible emission by the green light emitter [Tb III 2 (PBA) 6 ] and red light emitter [Eu III 2 (PBA) 6 ] could be controlled through pH adjustment. [Tb III 2 (PBA) 6 ] emitted only under acidic conditions, while [Eu III 2 (PBA) 6 ] emitted only under basic conditions. Taking advantage of Nafion's high proton conductivity brought about dynamic changes in the wavelengths emitted by the film. When an in-plane external voltage was applied to the film, red wavelength emission appeared to migrate toward the negative electrode. Owing to the proton concentration gradient induced by the electric field, emission by Eu III at 615 nm was enhanced near the positive electrode, whereas proton deficiency suppressed emission by [Tb III 2 (PBA) 6 ]. Tuneable emission in the transparent Nafion system enhances its potential for use as an energy-saving material.

Chemical Communications, 2021

Journal of Physical Chemistry B, Apr 26, 2019

Dalton Transactions, 2021

Functional metal–organic squares (MOSs) and metal–organic cubes (MOCs) are important building uni... more Functional metal–organic squares (MOSs) and metal–organic cubes (MOCs) are important building units for zeolite-like metal–organic frameworks (ZMOFs), which are required to exhibit solid-state properties, such as dielectric and magnetic properties.

Crystals, 2020

A transparent film allowing tunable multicolor emission based on a composite of an organometallic... more A transparent film allowing tunable multicolor emission based on a composite of an organometallic compound and a cation-exchange membrane has been developed, in which the cyclometallated iridium(III) complex [IrIII(4Py-ppy)3] (=tris[2-(2-pyridinyl-κN)-4-(4-pyridinyl)phenyl-κC]iridium) (1) with pH-dependent emission wavelengths has been incorporated into Nafion by cation exchange. Soaking Nafion in the solution of 1 for 24 h and exposed to buffers at pH 2, 4, and 10 resulted in maximum emission wavelengths of 587, 560, and 503 nm, respectively. The photophysical properties of 1@Nafion were also enhanced, as its maximum emission wavelength was more blue-shifted than those of 602, 564, and 503 nm in the solutions. The emission quantum yields (Φ) and lifetimes (τ) of 1@Nafion prepared under an acidic condition were up to Φ = 1.8% and τ = 0.11, 0.92 μs, which are considerably higher than the corresponding solutions of Φ = 0.5% and τ = 0.02, 0.18 μs. This is attributed to the fact that 1 ...

Chemistry Letters, 2020

A type of electron-accepting N-heteroacene which can be used as a bis-bidentate ligand, tetrapyri... more A type of electron-accepting N-heteroacene which can be used as a bis-bidentate ligand, tetrapyrido[3,2-a:2¤,3¤-c:3¤¤,2¤¤j:2¤¤¤,3¤¤¤-l] [5,6,11,12]tetraazanaphthacene (TPy-TANC), was synthesized. TPy-TANC is a pyridine-fused tetraazanaphthacene which has the potential to behave as an n-type semiconductor. TPy-TANC was determined to have a monoclinic P2 1 /n space group by single-crystal X-ray diffraction analysis. The cyclic voltammogram of [(bpy) 2 Ru II (TPy-TANC)Ru II (bpy) 2 ]-(PF 6 ) 4 (bpy = 2,2¤-bipyridine) showed a reversible four-step/ six-electron transfer in the reduction at ¹0.553 (1e ¹ , TPy-TANC), ¹1.15 (1e ¹ , TPy-TANC), ¹1.81 (2e ¹ , bpy), and ¹2.02 V (2e ¹ , bpy) (vs. Fc/Fc + ).

Chemical Communications, 2021

Materials, 2021

The structural and electronic properties of interfaces composed of donor and acceptor molecules p... more The structural and electronic properties of interfaces composed of donor and acceptor molecules play important roles in the development of organic opto-electronic devices. Epitaxial growth of organic semiconductor molecules offers a possibility to control the interfacial structures and to explore precise properties at the intermolecular contacts. 5,6,11,12-tetraazanaphthacene (TANC) is an acceptor molecule with a molecular structure similar to that of pentacene, a representative donor material, and thus, good compatibility with pentacene is expected. In this study, the physicochemical properties of the molecular interface between TANC and pentacene single crystal (PnSC) substrates were analyzed by atomic force microscopy, grazing-incidence X-ray diffraction (GIXD), and photoelectron spectroscopy. GIXD revealed that TANC molecules assemble into epitaxial overlayers of the (010) oriented crystallites by aligning an axis where the side edges of the molecules face each other along the [...

Dalton Transactions, 2019

For the cyclometallation reaction with the polyaromatic ligand to Ir(N^C) complexes, the steric b... more For the cyclometallation reaction with the polyaromatic ligand to Ir(N^C) complexes, the steric bulkiness determines whether the six-membered or five-membered N^C metallocycle is formed.

Chemistry – A European Journal, 2019

In the originally published manuscript, the name Yuki Ohata wasm isspelt as Yuki Ohhata,ane rror ... more In the originally published manuscript, the name Yuki Ohata wasm isspelt as Yuki Ohhata,ane rror that the authorsw ish to point out and correct herewith.

Scientific Reports, 2017

K3Cu3AlO2(SO4)4 is a highly one-dimensional spin-1/2 inequilateral diamond-chain antiferromagnet.... more K3Cu3AlO2(SO4)4 is a highly one-dimensional spin-1/2 inequilateral diamond-chain antiferromagnet. Spinon continuum and spin-singlet dimer excitations are observed in the inelastic neutron scattering spectra, which is in excellent agreement with a theoretical prediction: a dimer-monomer composite structure, where the dimer is caused by strong antiferromagnetic (AFM) coupling and the monomer forms an almost isolated quantum AFM chain controlling low-energy excitations. Moreover, muon spin rotation/relaxation spectroscopy shows no long-range ordering down to 90 mK, which is roughly three orders of magnitude lower than the exchange interaction of the quantum AFM chain. K3Cu3AlO2(SO4)4 is, thus, regarded as a compound that exhibits a Tomonaga-Luttinger spin liquid behavior at low temperatures close to the ground state.

Dalton Transactions, 2018

H-Bonded metal complex dimers with reversible redox behavior connected by an LBHB can provide a u... more H-Bonded metal complex dimers with reversible redox behavior connected by an LBHB can provide a unique mixed-valency state. However, the metal complexes substituted two H-bonding protons to two Ag+ions electrochemically have no mixed-valency state.

Inorganic Chemistry, 2017

A proton-coupled electron transfer (PCET) reaction was widely studied with isolated organic molec... more A proton-coupled electron transfer (PCET) reaction was widely studied with isolated organic molecules and metal complexes in solution in view of the biological catalytic reaction, while studying this reaction in the crystalline or solid-state phase, which has a novel example, would give insight into the rather internal environment of proteins without solvation and a creation of new molecular materials. We tried to crystallize a hydrogen-bonded (H-bonded) coordination polymer with one-dimensional nanoporous channels, formed from redox-active Ru III complexes, [Ru III (Hbim) 3 ] (Hbim -= 2,2′-biimidazolate monoanion). As a result, a synchronized collective PCET phenomenon was observed for the molecular nanoporous crystal by novel solid-state cyclic voltammetry (CV), which could be measured by only setting some crystals on the electrode surface. The nanoporous crystals, {[Ru III (Hbim) 3 ]} n (1), are simultaneously induced to a synchronized collective Ru II Ru III mixed-valence state, {Ru II Ru III } n , with alternating arrays of Ru II and Ru III complexes by PCET in a way of the reductive state of {Ru II Ru II } n . Further, a new crystal with {Ru II Ru III } n , {[Ru II (H 2 bim)(Hbim) 2 ][Ru III (bim) (Hbim) 2 ][K(MeOBz) 6 ]} n (2), was also prepared, and the solid-state CV revealed the same electrochemical behavior of {Ru II Ru III } n with 1. The single crystal with {Ru II Ru III } n of 2 was unusually a semiconductor with 5.12 × 10 -6 S/cm conductivity at 298 K by an impedance method (8.01 × 10 -6 S/cm by a direct-current method at 277 K). Thus, an unprecedented electron-hopping conductor driven by a lowbarrier proton transfer through a PCET mechanism (E a = 0.30 eV) was realized in the H-bonding molecular crystal with {Ru II Ru III } n . Such studies on a PCET reaction in the crystalline state is not only worthwhile as a model of essential biological reactions without solvation, but also proposed to a new design of molecular materials to occur an electron transfer by using an intermolecular H-bond.

Acta Crystallographica Section A Foundations of Crystallography, 2008

Tungsten trioxides and their alkali-metal-intercalated products MzWO3 + show potential for applic... more Tungsten trioxides and their alkali-metal-intercalated products MzWO3 + show potential for application in electrodes, as ion exchangers, catalysts and the treatment of radioactive waste. Hexagonal tungsten bronze (HTB) features hexagonal channels, of diameter ~0.54 nm, that may be useful for selective and reversible binding of metal ions. In particular doping of HTB with molybdenum (Mo-HTB) has been reported to enhance the uptake of Cs + and Sr 2+ . We have conducted a powder diffraction study, using both x-rays and neutrons on a series of MzHTB (M = Na + , Mn 2+ , Ba 2+ , Ce 3+ , Pb 2+ ), including some doped with molybdenum (Mo-HTB) synthesized using hydrothermal methods. Rietveld refinement of the diffraction patterns show that doping with Mo rapidly degrades the crystallinity of HTB by creating a high degree of disorder in the a-b planes, suggesting that the presence of Mo retards the hydrothermal crystallization process. The refinements confirm previous reports of an exchangeable metal ion binding site that displays varying degrees of affinity for the various metal ions studied. The solution binding affinity behaviour of the Mo-HTB's was also investigated for selected ions (M = Co 2+ , Gd 3+ , Ce 3+ , Ce 4+ Tl + , Pb 2+ doped with respective radiotracer) in a range of concentrations of acid and electrolytes solutions. These results show that the optimum condition for metal ion binding depends not only on the Mo doping level, but also the charge and redox chemistry of the exchange cation. In combination, the structure information and the solution chemistry indicate that the loading capacity of the each metal ion is also dependent on the microstructure of the HTB.

Inorganic chemistry, Jan 5, 2017

The judicious selection of pairs of benzimidazole-ligated ruthenium complexes allowed the constru... more The judicious selection of pairs of benzimidazole-ligated ruthenium complexes allowed the construction of a rechargeable proton-coupled electron-transfer (PCET)-type redox battery. A series of ruthenium(II) and -(III) complexes were synthesized that contain substituted benzimidazoles that engage in PCET reactions. The formation of intramolecular Ru-C cyclometalation bonds stabilized the resulting ruthenium(III) complexes, in which pKa values of the imino N-H protons on the benzimidazoles are usually lower than those for the corresponding ruthenium(II) complexes. As a proof-of-concept study for a solution redox battery based on such PCET reactions, the charging/discharging cycles of several pairs of ruthenium complexes were examined by chronopotentiometry in an H-type device with half-cells separated by a Nafion membrane in unbuffered CH3CN/H2O (1/1, v/v) containing 0.1 M NaCl. During the charging/discharging cycles, the pH value of the solution gradually changed accompanied by a cha...

Journal of Molecular Structure, 2013

We investigated the static structures and dynamic behaviors for guest molecules (CH 4 and CO 2 ) ... more We investigated the static structures and dynamic behaviors for guest molecules (CH 4 and CO 2 ) in small and large cavities which are composed of 12 pentagonal faces of 20 water molecules (5 12 ), and 12 pentagonal and 2 hexagonal faces of 24 water molecules (5 12 6 2 ), respectively, by B3LYP/6-311++G(d,p) level calculations in GAUSSIAN 09, and using quantum molecular dynamics (QMD) (NVT MD with semiempirical MO PM3 method). For the static calculations, the guest CO 2 and CH 4 molecules are around at the center of small and large cavities with weak H-bond formations of H-O-H···O 2 C and H 2 O···H 4 C van der Waals interaction systems. Calculated carbon NMR chemical shifts of the CH 4 in the gas-state and in the small and large cavities reflected the C-13 experimental tendency, while the calculated carbon NMR chemical shifts of the CO 2 in the three states almost correspond to the experimental value in the gas-state. For QMD calculations, we used a cluster model containing 73 water molecules, and examined dynamic behavior of guest molecules in the shell cluster model of 39 water molecules which own small and large cavities. The dynamic behavior of guest molecules are simulated from the trajectory distribution of molecular center of the mass due to the translational motion, and also analyzed using librational motions of guest molecules in the cavities.