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ABSTRACT: A phenalenyl radical with six methoxy groups, which were introduced symmetrically, has been synthesized. The extensively delocalized and highly symmetric electronic-spin system was studied with advanced cw-/pulsed-ESR techniques, thereby giving an experimental model to explore molecular quantum spin simulators with novel quantum coherence attributable to the extremely high degeneracy of the nuclear spin states owing to the eighteen equivalent protons.
Angewandte Chemie International Edition 04/2013; · 13.45 Impact Factor
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ABSTRACT: 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/(1)H-ENDOR/TRIPLE (electron paramagnetic resonance/(1)H-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 π 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.
Chemistry - An Asian Journal 03/2011; 6(5):1188-96. · 4.50 Impact Factor
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ABSTRACT: The film structure and electronic structure of a biradical hydrocarbon, diphenyl derivative of s-indacenodiphenalene (Ph(2)-IDPL) solid film has been investigated. A small energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) compared with that of typical π-conjugated small molecules was observed even for the amorphous film of Ph(2)-IDPL. This result indicates that the small HOMO-LUMO gap is an important characteristic of the singlet biradical electronic structure and well explains the previously reported ambipolar field effects of amorphous Ph(2)-IDPL film by Chikamatsu et al., Appl. Phys. Lett. 2007, 91, 043506. It was found that the gas-deposition method substantially improved the crystallinity of the film where Ph(2)-IDPL molecules form quasi one-dimensional (1D) molecular chains normal to the substrate surface. An extremely small HOMO-LUMO gap was observed in the polycrystalline Ph(2)-IDPL film, which is possibly caused by strong intermolecular coupling. The photon energy dependence of ultraviolet photoemission spectra shows that the stacked Ph(2)-IDPL molecular chain in the polycrystalline film develops an energy band structure in the direction of the surface normal of the film. The intermolecular covalency therefore evolves into the quasi 1D energy band along the molecular stacking direction.
Physical Chemistry Chemical Physics 10/2010; 12(39):12570-7. · 3.57 Impact Factor
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Akihiro Shimizu,
Takashi Kubo,
Mikio Uruichi,
Kyuya Yakushi,
Masayoshi Nakano,
Daisuke Shiomi,
Kazunobu Sato,
Takeji Takui,
Yasukazu Hirao,
Kouzou Matsumoto,
Hiroyuki Kurata,
Yasushi Morita, Kazuhiro Nakasuji
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ABSTRACT: 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 π-π 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 π-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 (1a). 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 Kekulé structure can be drawn for 2a.
Journal of the American Chemical Society 10/2010; 132(41):14421-8. · 9.91 Impact Factor
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ABSTRACT: 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···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.
Organic Letters 10/2010; 12(21):5036-9. · 5.86 Impact Factor
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ABSTRACT: Assembled metal complexes of 4,4′-biimidazole (4,4′-H2Bim), a ligand exhibiting multidirectional hydrogen-bonds, were investigated in AgI, CuII, and NiII complexes. The most intriguing feature of this system is that the directionality of hydrogen-bonds varies depending on the cis/trans-conformations of the ligand and the coordination geometries of the metal atoms. The [AgI2(4,4′-H2Bim)3] complex included ligands of both cis- and trans-conformations, the latter of which linked two metal atoms to form a planar dinuclear complex. The triple N−H···X···H−N hydrogen-bonds across the counteranions (X) formed a one-dimensional hydrogen-bond chain. The [CuII(4,4′-H2Bim)2] complexes showed a square-planar coordination sphere by the chelating coordination of two 4,4′-H2Bim units having the cis-conformation. The complexes were linked by the double N−H···X···H−N hydrogen-bonds across counteranions or solvent molecules to form one-dimensional chains. The [CuII(4,4′-HBim−)2] including the monodeprotonated ligand had a square-planar coordination geometry similar to those of [CuII(4,4′-H2Bim)2] complexes. The deprotonated nitrogen atom acted as a proton acceptor having a tetrahedral geometry. This complex formed a three-dimensional network by the π-stacks and N−H···O−H···N hydrogen-bonds across crystalline water molecules. The [NiII(4,4′-H2Bim)3] complexes had an octahedral coordination sphere including three chelating 4,4′-H2Bim ligands of the cis-conformation. The N−H···X···H−N hydrogen-bonds across counteranions established two- or three-dimensional networks.
09/2010;
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Angewandte Chemie International Edition 08/2010; 49(36):6333-7. · 13.45 Impact Factor
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Yasushi Morita,
Yumi Yakiyama,
Shigeaki Nakazawa,
Tsuyoshi Murata,
Tomoaki Ise,
Daisuke Hashizume,
Daisuke Shiomi,
Kazunobu Sato,
Masahiro Kitagawa, Kazuhiro Nakasuji,
Takeji Takui
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ABSTRACT: 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.
Journal of the American Chemical Society 05/2010; 132(20):6944-6. · 9.91 Impact Factor
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Angewandte Chemie International Edition 02/2010; 49(9):1678-82. · 13.45 Impact Factor
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Makoto Tadokoro,
Takashi Ohhara,
Yuhki Ohhata,
Takaaki Suda,
Yuji Miyasato,
Takeshi Yamada,
Tatsuya Kikuchi,
Ichiro Tanaka,
Kazuo Kurihara,
Masaharu Oguni, Kazuhiro Nakasuji,
Osamu Yamamuro,
Kuroki Ryota
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ABSTRACT: The movement of water molecules in the limited space present within nanoscale regions, which is different from the molecular motion of bulk water, is significantly affected by strong interfacial interactions with the surrounding outer walls. Hence, most of the water molecules that are confined to nanochannel spaces having widths less than ca. 2 nm can generally be classified together as "structural water". Since the motions of such water molecules are limited by interfacial interactions with the outer wall, the nature of structural water, which is strongly influenced by the interactions, will have different characteristics from normal water. For our investigations on the characteristics of structural water, we have developed a nanoporous crystal with a diameter of ca. 1.6 nm; it was constructed from 1-D hydrophilic channels by self-organization of the designed molecules. A tubelike three-layered water cluster, called a water nanotube (WNT), is formed in each internal channel space and is regulated by H-bonds with the outer wall. The WNT undergoes a glass transition (T(g) = 107 K) and behaves as a liquid; it freezes at 234 K and changes into an icelike nanotube cluster. In this study, the structure of the WNT is investigated through neutron structure analysis, and it is observed to stabilize by a mechanistic anchor effect of structural water. Furthermore, from neutron-scattering experiments, it is seen that a few water molecules around the center of the WNT move approximately with the same diffusion constant as those in bulk water; however, the residence time and average jump length are longer, despite the restrictions imposed by the H-bonding with structural water. The behavior of mobile water within a WNT is investigated; this can be used to elucidate the mechanism for the effect of structural water on vital functions on the cell surface.
The Journal of Physical Chemistry B 02/2010; 114(6):2091-9. · 3.70 Impact Factor
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ABSTRACT: The adsorption of a phenalenyl-based singlet biradical, 8,16-diphenyl-s-indaceno[1,2,3-cd:5,6,7-c′d′]diphenalene (Ph2-IDPL), on a highly oriented pyrolytic graphite surface has been studied using scanning tunneling microscopy (STM), tunneling spectroscopy, and ultraviolet photoelectron spectroscopy (UPS) under ultra-high-vacuum conditions. Ph2-IDPL molecules form a highly ordered monolayer on the graphite surface. The STM images of Ph2-IDPL monolayers show a strong bias-dependence in the range from −1.8 to +1.6 V. The observed image contrast may be associated with the distortion of the adsorption configuration or structural deformation of the molecules. UPS and tunneling spectroscopy reveal the electronic structure of Ph2-IDPL. The energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) was determined to be 2.7 eV from the measured peak-to-peak energy difference between the HOMO and LUMO in the tunneling spectrum.
01/2009;
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ABSTRACT: 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 1H and 13C 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.
Journal of the American Chemical Society 11/2008; 130(45):14954-5. · 9.91 Impact Factor
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ABSTRACT: Charge-transfer salts of protonated cations of 2,2′-disubstituted-4,4′-biimidazoles and oligo(imidazole)s with tetracyanoquinodimethane (TCNQ) were investigated to demonstrate the high potential of these systems for the regulation of molecular arrangement and electronic structure of charge-transfer salts. 4,4′-Biimidazole derivatives afforded six kinds of mixed-valent TCNQ salts exhibiting semiconducting behaviors. Structural analyses revealed that the protonated 4,4′-biimidazolium derivatives formed multidirectional and multidimensional hydrogen bonds with TCNQ, and constructed two kinds of self-assembled architectures: one-dimensional chainlike motifs involving TCNQ molecules and two-dimensional sheet structures composed of the alternation of segregated columns of 4,4′-biimidazolium and TCNQ. Furthermore, the hydrogen-bonding patterns regulated the electronic structures in TCNQ columns by strong cation−anion interaction, causing the nonuniform charge-distribution and semiconducting behaviors.
06/2008;
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Yasushi Morita,
Shuichi Suzuki,
Kozo Fukui,
Shigeaki Nakazawa,
Hiroshi Kitagawa,
Hideo Kishida,
Hiroshi Okamoto,
Akira Naito,
Akiko Sekine,
Yuji Ohashi,
Motoo Shiro,
Katsunari Sasaki,
Daisuke Shiomi,
Kazunobu Sato,
Takeji Takui, Kazuhiro Nakasuji
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ABSTRACT: Transition-metal complexes and organic radical molecules can be used to make electric conductors and ferromagnets, the optical properties of which can be controlled by changing temperature and are used as molecular switches and sensors. Whereas a number of organic radicals in solution show temperature-dependent optical properties, such behaviour in crystalline forms is more rare. 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.
Nature Material 02/2008; 7(1):48-51. · 32.84 Impact Factor
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Angewandte Chemie International Edition 02/2008; 47(11):2035-8. · 13.45 Impact Factor
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Yasushi Morita,
Shuichi Suzuki,
Kozo Fukui,
Shigeaki Nakazawa,
Hiroshi Kitagawa,
Hideo Kishida,
Hiroshi Okamoto,
Akira Naito,
Akiko Sekine,
Yuji Ohashi,
Motoo Shiro,
Katsunari Sasaki,
Daisuke Shiomi,
Kazunobu Sato,
Takeji Takui, Kazuhiro Nakasuji
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ABSTRACT: Transition-metal complexes and organic radical molecules can be used to make electric conductors and ferromagnets
Nature Material 12/2007; 7(1):48-51. · 32.84 Impact Factor
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ABSTRACT: 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 hydrogen-bonds and multiple S...S interactions and exhibited three-step oxidation processes and a high electrical conductivity as a single-component organic molecule.
Chemical Communications 11/2007; · 6.17 Impact Factor
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ABSTRACT: We prepared and isolated a phenalenyl-based neutral hydrocarbon (1 b) with a biradical index of 14%, as well as its charge-transfer (CT) complex 1 b-F(4)-TCNQ. The crystal structure and the small HOMO-LUMO gap assessed by electrochemical and optical methods support the singlet-biradical contribution to the ground state of the neutral 1 b. This biradical character suggests that 1 b has the electronic structure of phenalenyl radicals coupled weakly through an acetylene linker, that is, some independence of the two phenalenyl moieties. The monocationic species 1 b*+ was obtained by reaction with the organic electron acceptor F4-TCNQ. The cationic species has a small disproportionation energy deltaE for the reaction 2 x 1 b*+ <==> 1 b + 1 b2+, which presumably originates from the independence of the phenalenyl moieties. The small deltaE led to a small on-site Coulombic repulsion U(eff) = 0.61 eV in the CT complex. Moreover, a very effective orbital overlap of the phenalenyl rings between molecules afforded a relatively large transfer integral t = 0.09 eV. The small U(eff)/4t ratio (= 1.7) resulted in a metallic-like conductive behavior at around room temperature. Below 280 K, the CT complex showed a transition into a semiconductive state as a result of bond formation between phenalenyl and F4-TCNQ carbon atoms.
Chemistry - An Asian Journal 11/2007; 2(11):1370-9. · 4.50 Impact Factor
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ABSTRACT: Hydrogen-bond interaction in donor-acceptor charge-transfer complexes of TTF-imidazole demonstrated the electronic effects in terms of control of component ratio and redox activation. These unprecedented effects of hydrogen bonds renewed the criteria giving "a high probability of being organic metals" and produced a number of highly conductive complexes with various acceptors having a wide range of electron-accepting ability. In p-chloranil complex, both molecules were linked by hydrogen bonds and formed a D-A-D triad, regulating the donor-acceptor composition to be 2:1. Theoretical calculations have revealed that the polarizability of hydrogen bonds controls the redox ability of the donor and p-benzoquinone-type acceptors and afforded different ionicity in complexes from those expected by the difference of redox potentials between donor and acceptors. In the p-chloranil complex, this electronic and structural regulation by hydrogen bond realized the first metallic donor-acceptor charge-transfer complex based on hydrogen bond functionalized TTF. Hydrogen bonds controlled also molecular arrangements in charge-transfer complexes, giving diverse and highly ordered assembled structures, D-A-D triad in the p-chloranil complex, one-dimensional zigzag chain in I(5) salt, alternating donor-acceptor chain in chloranilic acid complex, and D-A-D-A cyclic tetramer in nitranilic acid complex. Furthermore, TTF-imidazole acted as electron donor as well as proton acceptor in anilic acid complexes and realized the simultaneous charge- and proton-transfer complexes. These investigations demonstrated the new and intriguing potentials of the hydrogen bond in the development of organic conductors and multifunctional molecular materials.
Journal of the American Chemical Society 10/2007; 129(35):10837-46. · 9.91 Impact Factor
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Masayoshi Nakano,
Nozomi Nakagawa,
Ryohei Kishi,
Suguru Ohta,
Masahito Nate,
Hideaki Takahashi,
Takashi Kubo,
Kenji Kamada,
Koji Ohta,
Benoît Champagne,
Edith Botek,
Yasushi Morita, Kazuhiro Nakasuji,
Kizashi Yamaguchi
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ABSTRACT: Adopting density functional theory and a hybrid exchange-correlation functional, the relationship between the second hyperpolarizability (gamma) and the diradical character has been investigated for diphenalenyl-based compounds containing different heterocyclic five-membered central rings (C(4)H(4)X, where X = NH, PH, O, S, CH(2), SiH(2), BH, GaH, C=O, C=S, and C=Se) or substituted by donor (NH(2))/acceptor(NO(2)) groups. It turns out that these structural modifications can tune the diradical character from 0.0 to 0.968 and lead to variations of gamma over more than 1 order of magnitude, demonstrating the controllability of gamma in this family of compounds. In particular, when the central ring is strongly aromatic, the diradical character is larger than 0.7, which is associated with pretty large gamma values except for almost the pure diradical case (y approximately 1). On the other hand, when the aromaticity decreases--or the antiaromaticity increases--the diradical character and the second hyperpolarizability get smaller. These relationships are correlated to structural (bond length alternation) and charge distribution (charge transfer between the phenalenyl rings and the central ring) properties, which account for the relative importance of the resonance diradical, zwitterionic, and quinoid forms. Therefore, the diradical character and the second hyperpolarizability can be controlled by the aromaticity of the ring while the paradigm of the enhancement of gamma for intermediate diradical character is globally verified. Then, upon introducing donor groups, the zwitterionic character increases, leading to closed-shell species and small second hyperpolarizabilities. In the case of substitution by acceptor groups, the charge transfer is reduced but the diradical character and the second hyperpolarizability hardly changes.
The Journal of Physical Chemistry A 10/2007; 111(37):9102-10. · 2.95 Impact Factor
