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ABSTRACT: Two kinds of octaazacyclophanes, octaaza[18]m,p,m,p,m,p,m,p- cyclophane 2 and octaaza[18]m,p,p,p,m,p,p,p-cyclophane 3, as ring-size extended congeners of tetraaza[14]m,p,m,p-cyclophane were synthesized, and the electronic states of their polycationic species were investigated by quantum chemical calculations, electrochemical measurements (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)), UV-vis-NIR spectroelectrochemical measurements, and pulsed electron spin resonance (ESR) spectroscopy. The present octaazacyclophanes exhibited multi-redox activities depending on different linkage patterns along the macrocyclic molecular skeletons, and both molecules were oxidizable up to octacation. Spectroelectrochemical measurements demonstrated that para-phenylenediamine (PD) moieties in 2 could be converted from the semi-quinoidal structure to quinoidal one with increasing oxidation number, whereas higher oxidation states of 3 did not show definite quinoidal deformation of PD moieties. Pulsed ESR spectrum gave the evidence about the formation of almost pure spin-triplet state for 32+, whereas the high-spin states of 22+ and 24+ are virtually degenerate with the competing low-spin states even at low temperatures, probably due to fragility of spin-coupling pathway caused by facile conformational changes.
The Journal of Organic Chemistry 03/2013; · 4.45 Impact Factor
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ABSTRACT: Spin doctor: The polymacrocyclic oligoarylamine in the picture serves as a multispin source owing to its multi-electron redox activity. As a result of its pseudobeltane structure and para-phenylenediamine bridges, the radical cation can convert between two sideslipped structures with a windshield-wiper-like motion. In contrast, the tetraazacyclophane units are rigid components in the polymacrocycle.
Angewandte Chemie International Edition 11/2012; · 13.45 Impact Factor
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ABSTRACT: The chemical reactivity in nucleophilic cycloaddition to C70 is investigated on the basis of vibronic (electron-vibration) coupling density and vibronic coupling constants. Since the e1'' LUMOs of C70 are doubly degenerate and delocalized throughout the molecule, it is difficult to predict the regioselectivity by the frontier orbital theory. It is found that vibronic coupling density analysis for the effective mode as a reaction mode illustrates the idea of a functional group embedded in the reactive sites. Furthermore, the vibronic coupling constants for localized stretching vibrational modes enable us to estimate the quantitative reactivity. These calculated results agree well with the experimental findings. The principle of chemical reactivity proposed by Parr and Yang is modified as follows: the preferred direction is the one for which the initial vibronic coupling density for a reaction mode of the isolated reactant is a minimum.
The Journal of Organic Chemistry 10/2012; · 4.45 Impact Factor
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ABSTRACT: Quantitative ab initio calculations are presented for the ultraviolet-visible peaks of cycl[3.2.2]azine and its mono- and dibenzannulated polycyclic compounds at the multistate CASPT2 (MS-CASPT2) level of theory, with 11 nm deviation from the experimental S(0) → S(1) absorption. The electrophilic substitution reactions of cycl[3.2.2]azine, benzo[a]/[g]annulated cycl[3.2.2]azines, and 6-dimethylamino[2.2.3]cyclazine-1-carboxylates with 3-cyano-4-methylthiomaleimide gave the corresponding functionalized cycl[3.2.2]azine derivatives, which exhibited the absorption maxima around 510-630 nm. The first intense peaks were investigated by means of time-dependent density functional theory (TD-DFT). These peaks were systematically underevaluated by ∼50 nm, within the acceptable accuracies of TD-DFT. Furthermore, we calculated vibronic coupling constants of the electronic excited states of cycl[3.2.2]azine and simulated absorption spectra both in vacuo and in ethanol. The solvent effect is found to enhance oscillator strengths and vibronic couplings. This is because the solvent effect gives rise to changes in the electron density difference on the phenyl ring, and in turn, the intensified overlap between the electron density difference and the potential derivative in the phenyl ring leads to enhanced vibronic couplings in ethanol.
The Journal of Physical Chemistry A 08/2012; · 2.95 Impact Factor
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ABSTRACT: The redox properties and electronic structures of polycationic species were examined using a triphenylamine double-decker species. The double-decker has a strong electron-donating ability, and the spin in the radical cation is delocalized over the whole caged skeleton, despite no direct transannular π-π interaction between two TPA decks. Moreover, the diradical dication has spin-singlet character, despite the meta-phenylene linkage.
Angewandte Chemie International Edition 08/2012; 51(37):9403-6. · 13.45 Impact Factor
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ABSTRACT: Double- and triple-decker oligoarylamines have been prepared and characterized by X-ray crystallography for the first time (see picture; C black, N blue). The N-dianisylaminophenyl-substituted double decker exhibited the multiredox activity, and the oxidized species were confirmed to be in high-spin states on the basis of pulsed ESR spectroscopy.
Angewandte Chemie International Edition 07/2012; 51(33):8281-5. · 13.45 Impact Factor
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ABSTRACT: Vibronic couplings in C(60)(-) anion are discussed on the basis of the concept of the vibronic coupling density (VCD) [T. Sato, K. Tokunaga, and K. Tanaka, J. Chem. Phys. 124, 024314 (2006); K. Tokunaga, T. Sato, and K. Tanaka, J. Chem. Phys. 124, 154303 (2006); and T. Sato, K. Tokunaga, and K. Tanaka, J. Phys. Chem. A 112, 758 (2008)]. The VCD analysis clearly reveals that the coupling to the bending h(g)(2) mode is weaker than the coupling to the stretching h(g)(7) and h(g)(8) modes. For the vibronic couplings with the stretching modes, polarizations of the electron density difference on the bonds play a crucial role in the vibronic couplings. Such a polarized electron density difference appears as a result of the Coulomb interactions between the electrons in the lowest unoccupied molecular orbital and relevant doubly-occupied orbitals.
The Journal of chemical physics 05/2012; 136(17):174315. · 3.09 Impact Factor
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ABSTRACT: Vibronic coupling constants in the monoanionic, trianionic, and excited
states of picene are evaluated from the total energy gradients using the
density functional theory. Employing the calculated vibronic coupling constants
in the excited state of the neutral molecule, electron energy loss spectrum
(EELS) is simulated to be compared with the experimental spectrum. The
calculated vibronic coupling constants are analyzed in terms of the vibronic
coupling density which enables us to analyze vibronic couplings based on the
relation between the electronic and vibrational structures. The vibronic
coupling constants reported by Kato et al. [J. Chem. Phys. 116, 3420 (2002) and
Phys. Rev. Lett. 107, 077001 (2011)] are critically discussed based on the
vibronic coupling density analysis.
Phys. Rev. B. 03/2012; 85(16).
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ABSTRACT: The carbon-oxygen double bond of ketones (R(2)C=O) makes them among the most important organic compounds, but their homologues, heavy ketones with an E=O double bond (E = Si, Ge, Sn or Pb), had not been isolated as stable compounds. Their unavailability as monomeric molecules is ascribed to their high tendency for intermolecular oligomerization or polymerization via opening of the E=O double bond. Can such an intermolecular process be inhibited by bulky protecting groups? We now report that it can, with the first isolation of a monomeric germanium ketone analogue (Eind)(2)Ge=O (Eind = 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl), stabilized by appropriately designed bulky Eind groups, with a planar tricoordinate germanium atom. Computational studies and chemical reactions suggest the Ge=O double bond is highly polarized with a contribution of a charge-separated form (Eind)(2)Ge(+)-O(-). The germanone thus exhibits unique reactivities that are not observed with ordinary ketones, including the spontaneous trapping of CO(2) gas to provide a cyclic addition product.
Nature Chemistry 01/2012; 4(5):361-5. · 20.52 Impact Factor
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Yoshihiro Matano,
Kazuaki Matsumoto,
Hironobu Hayashi,
Yoshihide Nakao,
Tatu Kumpulainen,
Vladimir Chukharev,
Nikolai V Tkachenko,
Helge Lemmetyinen,
Soji Shimizu,
Nagao Kobayashi,
Daisuke Sakamaki,
Akihiro Ito, Kazuyoshi Tanaka,
Hiroshi Imahori
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ABSTRACT: 5-(Diphenylphosphanyl)-10,15,20-triarylporphyrins (meso-phosphanylporphyrins) underwent complexations with palladium(II) and platinum(II) salts to afford phosphapalladacycle- and phosphaplatinacycle-fused coplanar porphyrin dimers, respectively, via regioselective peripheral β-C-H activation of the meso-phosphanylporphyrin ligands. The optical and electrochemical properties of these metal-linked porphyrin dimers as well as their porphyrin monomer/dimer references were investigated by means of steady-state UV-vis absorption/fluorescence spectroscopy, cyclic and differential pulse voltammetry, time-resolved spectroscopy (fluorescence and transient absorption lifetimes and spectra), and magnetic circular dichroism spectroscopy. All the observed data clearly show that the palladium(II) and platinum(II) linkers play crucial roles in the electronic communication between two porphyrin chromophores at the one-electron oxidized state and in the singlet-triplet intersystem-crossing process at the excited state. It has also been revealed that the C-Pt-C linkage makes more significant impacts on these fundamental properties than the C-Pd-C linkage. Furthermore, density functional theory calculations on the metal-linked porphyrin dimers have suggested that the antibonding dπ-pπ orbital interaction between the peripherally attached metal and adjacent pyrrolic β-carbon atoms destabilizes the highest occupied molecular orbitals of the porphyrin π-systems and accounts for the observed unique absorption properties. On the basis of these experimental and theoretical results, it can be concluded that the linear carbon-metal-carbon linkages weakly but definitely perturb the optical, photophysical, and electrochemical properties of the phosphametallacycle-linked coplanar porphyrin dimers.
Journal of the American Chemical Society 12/2011; 134(3):1825-1839. · 9.91 Impact Factor
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ABSTRACT: Diborane(6) as a H-bridged dimer of monoborane can be converted cleanly by two-electron reduction into diborane(6) dianion, which is isoelectronic with ethane, through B-B σ-bond formation when each boron atom has a bulky ligand on it. The existence of the B-B σ bond is supported by the X-ray molecular structure [B-B bond length of 1.924(3) Å], NMR studies, magnetic susceptibility measurements, and DFT calculations. Stepwise hydride abstraction reactions of the diborane(6) dianion produce the corresponding H-bridged diborane(5) anion and doubly H-bridged diborane(4) without B-B bond scission.
Journal of the American Chemical Society 06/2011; 133(29):11058-61. · 9.91 Impact Factor
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ABSTRACT: A profusion of phospholes: Diacenaphtho[1,2-b:1',2'-d]phospholes, a new class of arene-fused phosphole π-systems, were synthesized and their structural and electrochemical properties studied. The P-sulfide derivative has a high electron-transporting ability (μ(E) =2.4×10(-3) cm(2) V(-1) s(-1) ) in a vacuum-deposited film.
Angewandte Chemie International Edition 06/2011; 50(35):8016-20. · 13.45 Impact Factor
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ABSTRACT: p-Monothiobenzoquinones incorporated in a fused-ring octaalkyl-s-hydrindacene skeleton have been synthesized as air- and moisture-stable reddish orange crystals by the oxidation of mercaptophenol derivatives with DDQ, which have been characterized by X-ray crystallography to show a planar quinoid framework.
Organic Letters 05/2011; 13(10):2666-9. · 5.86 Impact Factor
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ABSTRACT: The cyclobutadiene (CBD) molecule C(4)H(4) deviates from a high-symmetry square geometry to compensate for its antiaromatic electronic structure. Here, we report a CBD silicon analog, Si(4)(EMind)(4) (1), stabilized by the bulky 1,1,7,7-tetraethyl-3,3,5,5-tetramethyl-s-hydrindacen-4-yl (EMind) groups, obtained as air- and moisture-sensitive orange crystals by the reduction of (EMind)SiBr(3) with three equivalents of lithium naphthalenide. X-ray crystallography reveals a planar and rhombic structure of the Si(4) four-membered ring, with alternating pyramidal and planar configurations at the silicon atoms. The large (29)Si chemical shift differences (Δδ > 350 parts per million) in the solid-state nuclear magnetic resonance spectra suggest a contribution of an alternately charge-separated structure. The rhombic-shaped charge-separated singlet state of compound 1 thus stabilizes its cyclic 4π-electron antiaromaticity in a manner that contrasts sharply with the bond-length alternation, characterizing the rectangular distortion of carbon-based CBD.
Science 03/2011; 331(6022):1306-9. · 31.20 Impact Factor
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ABSTRACT: Two kinds of basic dendritic (or starburst) all-para-phenylene-linked oligotriarylamines, which are generated from para-phenylenediamine and triphenylamine as core units, respectively, were prepared, and the electrochemical, spectroelectrochemical, ESR spectroscopic measurements were carried out with respect to their application as hole transport materials in optoelectronic devices such as organic light-emitting devices. The prepared dendritic oligoarylamines exhibits the multiredox-active properirs, and are stably oxidizable up to tetra- or hexacations. According to the degree of oxidation, it was suggested that the charge distribution of the charged states gradually change so as to reduce the electrostatic repulsion between increased charges on the basis of the spectroelectrochemical studies. Moreover, the stability of the generated radical cations and the spin distribution in their radical cations were confirmed by the ESR measurements.
12/2010;
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ABSTRACT: The vibronic coupling constants of C60− are derived from the photoelectron spectrum measured by Wang et al. J. Chem. Phys. 123 051106 (2005) at low temperature with high resolutions. We find that the couplings of the Jahn-Teller modes of C60− are weaker than the couplings reported by Gunnarsson et al. Phys. Rev. Lett. 74 1875 (1995). The total stabilization energy after hg and ag modes is reduced with respect to the previous derivation of Gunnarsson et al. by 30%. The computed vibronic coupling constants using density-functional theory with B3LYP functional agree well with the new experimental constants, so the discrepancy between theory and experiment persistent in the previous studies is basically solved.
Phys. Rev. B. 12/2010; 82(24).
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Angewandte Chemie International Edition 10/2010; 49(44):8205-8. · 13.45 Impact Factor
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ABSTRACT: We calculate inelastic electron tunneling (IET) spectra for 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and tetrathiafulvalene dithiol (TTF-DT) sandwiched between two gold electrodes using non-equilibrium Green's function (NEGF) theory. The calculated peak positions are in reasonable agreement with the experimental data. We also calculate IET spectrum for thiophene dithiol (Th-DT) sandwiched between two gold electrodes and compare it with that for the Au/DMcT/Au junction. Th-DT and DMcT can be distinguished using the IET spectroscopy by the peak of the C-C stretching mode. The peak intensity in the IET spectra is analyzed using vibronic coupling density (VCD) analysis. For the Au/DMcT/Au junction, large distribution of electron-density difference Δρ(HOMO) on the C-N bond is responsible for the intense peak of the C-N stretching mode; on the other hand, for Au/TTF-DT/Au junction, large distribution of Δρ(HOMO) on the central C=C bond is responsible for the intense peak of the C=C stretching modes.
Nanoscale 10/2010; 2(10):2186-94. · 5.91 Impact Factor
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ABSTRACT: π-Conjugated disilenes with 2-naphthyl or 2-fluorenyl groups on the silicon atoms have been synthesized as air-stable emissive red solids using the bulky 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (Eind) groups. The strong π-π* absorptions and distinct emission at room temperature, both in solution and in the solid state, have been observed due to the substantial contribution of the 3p(π)*(Si-Si)-2p(π)*(carbon π-electron system) conjugation.
Journal of the American Chemical Society 10/2010; 132(43):15162-3. · 9.91 Impact Factor
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ABSTRACT: para-Phenylene-bridged spirobi(triarylamine) dimer 2, in which π conjugation through four redox-active triarylamine subunits is partially segregated by the unique perpendicular conformation, was prepared and characterized by structural, electrochemical, and spectroscopic methods. Quantum chemical calculations (DFT and CASSCF) predicted that the frontier molecular orbitals of 2 are virtually fourfold degenerate, so that the oxidized states of 2 can give intriguing electronic and magnetic properties. In fact, the continuous-wave ESR spectroscopy of radical cation 2(*+) showed that the unpaired electron was trapped in the inner two redox-active dianisylamine subunits, and moreover was fully delocalized over them. Magnetic susceptibility measurements and pulsed ESR spectroscopy of the isolated salts of 2, which can be prepared by treatment with SbCl(5), revealed that the generated tetracation 2(4+) decomposed mainly into a mixture of 1) a decomposed tetra(radical cation) consisting of a tri(radical cation) moiety and a trianisylamine radical cation moiety (≈75%) and 2) a diamagnetic quinoid dication in a tetraanisyl-p-phenylendiamine moiety and two trianisylamine radical cation moieties (≈25%). Furthermore, the spin-quartet state of the tri(radical cation) moiety in the decomposed tetra(radical cation) was found to be in the ground state lying 30 cal mol(-1) below the competing spin-doublet state.
Chemistry 09/2010; 16(35):10866-78. · 5.93 Impact Factor
