-
[show abstract]
[hide abstract]
ABSTRACT: A triangulene-based C2 -symmetric 33 π-conjugated stable neutral π-radical, 2(.) , which possesses two dicyanomethylene groups and one oxo group, has been designed, synthesized, and isolated as an analogue of tris(dicyanomethylene) derivative 1(.) and trioxo derivative TOT(.) with C3 symmetry. Effects of molecular-symmetry reduction and electron-accepting substituents on this fused polycyclic neutral π-radical system were studied in terms of their molecular structure, electronic-spin structure, and electrochemical and optical properties with the help of theoretical calculations. Interestingly, this system (2(.) ) has a four-stage redox ability, like TOT(.) , as well as low frontier energy levels and a small SOMO-LUMO gap, similar to 1(.) , in spite of the loss of the degenerate LUMOs in symmetry-lowered 2(.) , which is associated with the attachment of the weaker electron-accepting oxo group instead of the dicyanomethylene group in 1(.) . These prominent results are attributable to the structural and electronic properties in the triangulene-based highly delocalized fused polycyclic neutral π-radical system.
Chemistry - An Asian Journal 06/2013; · 4.50 Impact Factor
-
[show abstract]
[hide abstract]
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
-
[show abstract]
[hide abstract]
ABSTRACT: Made to order: Rechargeable batteries are fabricated by using organic electron acceptors and donors as active cathode materials. Their output voltage and cycle performance can be tuned by organic chemistry techniques. The output voltages are linked to both the redox potentials and the energy levels of the frontier molecular orbitals of the cathode materials, enabling to predict the output voltage at an early stage of the design.
ChemSusChem 03/2013; · 6.83 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Radically active: A redox-active air-stable neutral π radical 1(.) with three dicyanomethylene groups introduced with threefold symmetry into a triangulene π skeleton instead of the oxygen atoms of TOT(.) was designed, synthesized and characterized. The enhanced electron-accepting ability and extended π-electronic system of this chemical modification gave an extremely small SOMO-LUMO gap and significantly lowered the frontier orbital energies, leading to the remarkable increase in the redox stages.
Chemistry 11/2012; · 5.93 Impact Factor
-
Shigeaki Nakazawa,
Shinsuke Nishida,
Tomoaki Ise,
Tomohiro Yoshino,
Nobuyuki Mori,
Robabeh D Rahimi,
Kazunobu Sato, Yasushi Morita,
Kazuo Toyota,
Daisuke Shiomi,
Masahiro Kitagawa,
Hideyuki Hara,
Patrick Carl,
Peter Höfer,
Takeji Takui
[show abstract]
[hide abstract]
ABSTRACT: A quantum gate: A system of two coupled electron spins that is useful for simple quantum computing operations has been prepared by synthesis of a biradical 1 and co-crystallization with an isomorphous host molecule. The two weakly exchange-coupled quantum bits (target qubit blue and control qubit red) span four electron spin states. The electron spin transition is denoted by two black arrows.
Angewandte Chemie International Edition 08/2012; 51(39):9860-4. · 13.45 Impact Factor
-
Kazuki Ayabe,
Kazunobu Sato,
Shinsuke Nishida,
Tomoaki Ise,
Shigeaki Nakazawa,
Kenji Sugisaki, Yasushi Morita,
Kazuo Toyota,
Daisuke Shiomi,
Masahiro Kitagawa,
Takeji Takui
[show abstract]
[hide abstract]
ABSTRACT: 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 ω(1) (angular frequency) for any cases of weakly exchange-coupled systems can be classified into three categories; D(12) (spin dipolar interaction)-driven, Δg-driven and ω(1)-driven nutation behaviour with the increasing strength of ω(1). For hetero-spin biradicals, Δg 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 ω(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)H(3))methyl]-[3,3-(2)H(2),4-(2)H(1),5,5-(2)H(2)]piperidin-N-oxyl-4-yl)(2,2,6,6-tetra[((2)H(3))methyl]-[3,3-(2)H(2),4-(2)H(1),5,5-(2)H(2),(15)N]piperidin-(15)N-oxyl-4-yl) terephthalate in a toluene glass, with a distance of 1.69 nm between the two spin sites is D(12) = -32 MHz (the effect of the exchange coupling J(12) is vanishing due to the homo-spin sites of 1, i.e.Δg = 0), while 0 < |J(12)|≦ 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.
Physical Chemistry Chemical Physics 05/2012; 14(25):9137-48. · 3.57 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new spin on an old system: The title neutral radicals have been synthesized and characterized for the first time. Thanks to two terminal methoxy groups and three tert-butyl groups, the chiral radicals are configurationally and chemically stable. The three-dimensional π-electron network shows extensive spin delocalization, and the distinct CD properties are attributed to the chirality of the helicene unit.
Angewandte Chemie International Edition 05/2012; 51(27):6691-5. · 13.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Secondary batteries using organic electrode-active materials promise to surpass present Li-ion batteries in terms of safety and resource price. The use of organic polymers for cathode-active materials has already achieved a high voltage and cycle performance comparable to those of Li-ion batteries. It is therefore timely to develop approaches for high-capacity organic materials-based battery applications. Here we demonstrate organic tailored batteries with high capacity by using organic molecules with degenerate molecular orbitals (MOs) as electrode-active materials. Trioxotriangulene (TOT), an organic open-shell molecule, with a singly occupied MO (SOMO) and two degenerate lowest-unoccupied MOs (LUMOs) was investigated. A tri-tert-butylated derivative ((t-Bu)(3)TOT)exhibited a high discharge capacity of more than 300 A h kg(-1), exceeding those delivered by Li-ion batteries. A tribrominated derivative (Br(3)TOT) was also shown to increase the output voltage and cycle performance up to 85% after 100 cycles of the charge-discharge processes.
Nature Material 12/2011; 10(12):947-51. · 32.84 Impact Factor
-
10/2011: pages 95 - 134; , ISBN: 9781118011263
-
[show abstract]
[hide abstract]
ABSTRACT: Graphene, a two-dimensional layer of sp(2)-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.
Nature Chemistry 03/2011; 3(3):197-204. · 20.52 Impact Factor
-
[show abstract]
[hide abstract]
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
-
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
[show abstract]
[hide abstract]
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
-
[show abstract]
[hide abstract]
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
-
[show abstract]
[hide abstract]
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;
-
Angewandte Chemie International Edition 08/2010; 49(36):6333-7. · 13.45 Impact Factor
-
Yasushi Morita,
Yumi Yakiyama,
Shigeaki Nakazawa,
Tsuyoshi Murata,
Tomoaki Ise,
Daisuke Hashizume,
Daisuke Shiomi,
Kazunobu Sato,
Masahiro Kitagawa,
Kazuhiro Nakasuji,
Takeji Takui
[show abstract]
[hide abstract]
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
-
Angewandte Chemie International Edition 02/2010; 49(9):1678-82. · 13.45 Impact Factor
-
[show abstract]
[hide abstract]
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;
-
[show abstract]
[hide abstract]
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
-
[show abstract]
[hide abstract]
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;
