Hiroshi Imahori

Publications of Hiroshi Imahori

• Development of a novel composite material with carbon nanotubes assisted by self-assembled peptides designed in conjunction with β-sheet formation.

  Authors: Yasuhiko Hashida, Tomokazu Umeyama, Junya Mihara, Hiroshi Imahori, Masahiko Tsujimoto, Seiji Isoda, Mikio Takano, Mitsuru Hashida

  Journal of pharmaceutical sciences. 04/2012;

  A novel composite material is developed with single-walled carbon nanotubes (SWCNTs) and artificially designed peptides, and its chemical and physicochemical characteristics are evaluated with an aimA novel composite material is developed with single-walled carbon nanotubes (SWCNTs) and artificially designed peptides, and its chemical and physicochemical characteristics are evaluated with an aim toward biomedical application. The peptides were designed to form a β-sheet structure that would be suitable for wrapping SWCNTs. The complex of SWCNTs and peptide (SWCNT-peptide) showed good dispersibility in aqueous media and was considerably stable even in the absence of an excess amount of peptide in the media. The formation of SWCNT-peptide was confirmed by its performance in water, atomic force microscopy and transmission electron microscopy observation, and molecular modeling. The possibility of introducing various functions to SWCNT-peptide was also demonstrated by several methods, such as introduction of special amino acids, chemical modification, and additional complex formation based on electrostatic interaction. These results suggest the potential of the SWCNT-peptide complex as a molecular platform on which a desirable structure and/or function can be constructed for biomedical and industrial application. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci.

• Nickel(II) and Copper(II) Complexes of β-Unsubstituted 5,15-Diazaporphyrins and Pyridazine-Fused Diazacorrinoids: Metal-Template Syntheses and Peripheral Functionalizations.

  Authors: Yoshihiro Matano, Tarou Shibano, Haruyuki Nakano, Hiroshi Imahori

  Chemistry (Weinheim an der Bergstrasse, Germany). 03/2012;

  The present paper reports the first comprehensive study on the synthesis, structures, optical and electrochemical properties, and peripheral functionalizations of nickel(II) and copper(II) complexesThe present paper reports the first comprehensive study on the synthesis, structures, optical and electrochemical properties, and peripheral functionalizations of nickel(II) and copper(II) complexes of β-unsubstituted 5,15-diazaporphyrins (M-DAP; M=Ni, Cu) and pyridazine-fused diazacorrinoids (Ni-DACX; X=N, O). These two classes of compounds were constructed starting from mesityldipyrromethane by a metal-template method. Ni-DAP and Cu-DAP were prepared in high yields by the reaction of the respective metal-bis(dibromodipyrrin) complexes with NaN(3) -CuX (X=I, Br), whereas Ni-DACN and Ni-DACO were formed as predominant products by the reaction with NaN(3) . In both cases, the metal centers change their geometry from tetrahedral to square planar during the aza-annulation; X-ray crystallographic analyses of M-DAPs showed highly planar diazaporphyrin π planes. The Q band of Ni-DAP was redshifted and intensified compared with that of a nickel-porphyrin reference, due to the involvement of electronegative nitrogen atoms at the meso positions. It was found that the peripheral bromination of Ni-DAP and Ni-DACO occurred regioselectively to afford Ni-DAP-Br(4) and Ni-DACO-Br, respectively. These brominated derivatives underwent Stille reactions with tributyl(phenyl)stannane to give the corresponding phenylated derivatives, Ni-DAP-Ph(4) and Ni-DACO-Ph. On the basis of the absorption spectra and X-ray analysis, it has been concluded that the attached phenyl groups efficiently conjugate with the diazaporphyrin π system. The present results unambiguously corroborate that the β-unsubstituted DAPs and DACXs are promising platforms for the development of a new class of π-conjugated azaporphyrin-based materials.

• Utilization of Photoinduced Charge-Separated State of Donor-Acceptor-Linked Molecules for Regulation of Cell Membrane Potential and Ion Transport.

  Authors: Tomohiro Numata, Tatsuya Murakami, Fumiaki Kawashima, Nobuhiro Morone, John E Heuser, Yuta Takano, Kei Ohkubo, Shunichi Fukuzumi, Yasuo Mori, Hiroshi Imahori

  Journal of the American Chemical Society. 03/2012;

  The control of ion transport across cell membranes by light is an attractive strategy that allows targeted, fast control of precisely defined events in the biological membrane. Here we report a novelThe control of ion transport across cell membranes by light is an attractive strategy that allows targeted, fast control of precisely defined events in the biological membrane. Here we report a novel general strategy for the control of membrane potential and ion transport by using charge-separation molecules and light. Delivery of charge-separation molecules to the plasma membrane of PC12 cells by a membranous nanocarrier and subsequent light irradiation led to depolarization of the membrane potential as well as inhibition of the potassium ion flow across the membrane. Photoregulation of the cell membrane potential and ion transport by using charge-separation molecules is highly promising for control of cell functions.

• Self-assembling porphyrins and phthalocyanines for photoinduced charge separation and charge transport.

  Authors: Hiroshi Imahori, Tomokazu Umeyama, Kei Kurotobi, Yuta Takano

  Chemical communications (Cambridge, England). 03/2012; 48(34):4032-45.

  Large π-conjugated compounds are promising building blocks for organic thin-film electronics such as organic light-emitting diodes, organic field-effect transistors, and organic photovoltaics.Large π-conjugated compounds are promising building blocks for organic thin-film electronics such as organic light-emitting diodes, organic field-effect transistors, and organic photovoltaics. Utilization of porphyrins and phthalocyanines for this purpose is highly fascinating because of their excellent electric, photophysical, and electrochemical properties as well as intense self-assembling abilities arising from π-π stacking interactions. This paper focuses on fundamental aspects of self-assembled structures that have been obtained from porphyrin and phthalocyanine building blocks and more complex composites for photoinduced charge separation and charge transport toward the potential applications to organic thin-film electronics.

• Preparation and photophysical and photoelectrochemical properties of a covalently fixed porphyrin-chemically converted graphene composite.

  Authors: Tomokazu Umeyama, Junya Mihara, Noriyasu Tezuka, Yoshihiro Matano, Kati Stranius, Vladimir Chukharev, Nikolai V Tkachenko, Helge Lemmetyinen, Kei Noda, Kazumi Matsushige, Tetsuya Shishido, Zheng Liu, Kaori Hirose-Takai, Kazu Suenaga, Hiroshi Imahori

  Chemistry (Weinheim an der Bergstrasse, Germany). 02/2012; 18(14):4250-7.

  Chemically converted graphene (CCG) covalently linked with porphyrins has been prepared by a Suzuki coupling reaction between iodophenyl-functionalized CCG and porphyrin boronic ester. The covalentlyChemically converted graphene (CCG) covalently linked with porphyrins has been prepared by a Suzuki coupling reaction between iodophenyl-functionalized CCG and porphyrin boronic ester. The covalently linked CCG-porphyrin composite was designed to possess a short, rigid phenylene spacer between the porphyrin and the CCG. The composite material formed stable dispersions in DMF and the structure was characterized by spectroscopic, thermal, and microscopic measurements. In steady-state photoluminescence spectra, the emission from the porphyrin linked to the CCG was quenched strongly relative to that of the porphyrin reference. Fluorescence lifetime and femtosecond transient absorption measurements of the porphyrin-linked CCG revealed a short-lived porphyrin singlet excited state (38 ps) without yielding the porphyrin radical cation, thereby substantiating the occurrence of energy transfer from the porphyrin excited state to the CCG and subsequent rapid decay of the CCG excited state to the ground state. Consistently, the photocurrent action spectrum of a photoelectrochemical device with a SnO(2) electrode coated with the porphyrin-linked CCG exhibited no photocurrent response from the porphyrin absorption. The results obtained here provide deep insight into the interaction between graphenes and π-conjugated systems in the excited and ground states.

• Effects of carbon-metal-carbon linkages on the optical, photophysical, and electrochemical properties of phosphametallacycle-linked coplanar porphyrin dimers.

  Authors: 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

  Journal of the American Chemical Society. 12/2011; 134(3):1825-39.

  5-(Diphenylphosphanyl)-10,15,20-triarylporphyrins (meso-phosphanylporphyrins) underwent complexations with palladium(II) and platinum(II) salts to afford phosphapalladacycle- and5-(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.

• Segregated donor-acceptor columns in liquid crystals that exhibit highly efficient ambipolar charge transport.

  Authors: Hironobu Hayashi, Wataru Nihashi, Tomokazu Umeyama, Yoshihiro Matano, Shu Seki, Yo Shimizu, Hiroshi Imahori

  Journal of the American Chemical Society. 06/2011; 133(28):10736-9.

  Liquid crystalline donor (i.e., phthalocyanine) was covalently linked to acceptor (i.e, fullerene) to achieve efficient charge-transport properties in a liquid crystalline phase. The columnarLiquid crystalline donor (i.e., phthalocyanine) was covalently linked to acceptor (i.e, fullerene) to achieve efficient charge-transport properties in a liquid crystalline phase. The columnar structure exhibited highly efficient ambipolar charge-transport character, demonstrating the potential utility of the strategy in organic electronics.

• Fusion of Phosphole and 1,1'-Biacenaphthene: Phosphorus(V)-Containing Extended π-Systems with High Electron Affinity and Electron Mobility.

  Authors: Yoshihiro Matano, Arihiro Saito, Tatsuya Fukushima, Yasuaki Tokudome, Furitsu Suzuki, Daisuke Sakamaki, Hironori Kaji, Akihiro Ito, Kazuyoshi Tanaka, Hiroshi Imahori

  Angewandte Chemie (International ed. in English). 06/2011;

• Bisquinoxaline-fused porphyrins for dye-sensitized solar cells.

  Authors: Hiroshi Imahori, Hiroaki Iijima, Hironobu Hayashi, Yuuki Toude, Tomokazu Umeyama, Yoshihiro Matano, Seigo Ito

  ChemSusChem. 06/2011; 4(6):797-805.

  5,10,15,20-Tetrakis(2,4,6-trimethylphenyl)-6'-carboxylquinoxalino[2,3-b]quinoxalino[12,13-b']porphyrinatozinc(II) (ZnPBQ) is synthesized to evaluate the effects of π elongation of quinoxaline-fused5,10,15,20-Tetrakis(2,4,6-trimethylphenyl)-6'-carboxylquinoxalino[2,3-b]quinoxalino[12,13-b']porphyrinatozinc(II) (ZnPBQ) is synthesized to evaluate the effects of π elongation of quinoxaline-fused porphyrins on the optical, electrochemical, and photovoltaic properties. ZnPBQ showed an intensified Soret band as well as red-shifted Soret and Q bands relative to 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)-6'-carboxylquinoxalino[2,3-b]porphyrinatozinc(II) (ZnPQ), demonstrating the improved light-harvesting property of ZnPBQ. The optical and electrochemical HOMO-LUMO gaps were consistent with those estimated by DFT calculations. The photovoltaic properties were compared under optimized conditions, in which a sealed device structure with TiCl(4) -treated, TiO(2) double layers was used. The ZnPBQ cell exhibited a relatively high power conversion efficiency (η) of 4.7%, which was smaller than that of the ZnPQ cell (η=6.3%). The weaker electronic coupling between the LUMO of ZnPBQ and conduction band (CB) of TiO(2) or more tilted geometry of ZnPBQ on the TiO(2) surface may result in the low electron injection/charge collection efficiency as well as the low incident photon-to-current efficiency (IPCE) for the ZnPBQ cell (maximum IPCE=56%) relative to the ZnPQ cell (maximum IPCE=75%), leading to the lower η value of the ZnPBQ cell than that of the ZnPQ cell. In addition, the open-circuit potential of the ZnPBQ cell also slightly decreased with the effect of charge recombination from the electrons injected into the CB of TiO(2) to I(3)(-).

• Electron transfer cascade by organic/inorganic ternary composites of porphyrin, zinc oxide nanoparticles, and reduced graphene oxide on a tin oxide electrode that exhibits efficient photocurrent generation.

  Authors: Hironobu Hayashi, Ian V Lightcap, Masahiko Tsujimoto, Mikio Takano, Tomokazu Umeyama, Prashant V Kamat, Hiroshi Imahori

  Journal of the American Chemical Society. 05/2011; 133(20):7684-7.

  A bottom-up strategy has been developed to construct a multiple electron transfer system composed of organic/inorganic ternary composites (porphyrin, zinc oxide nanoparticles, reduced graphene oxide)A bottom-up strategy has been developed to construct a multiple electron transfer system composed of organic/inorganic ternary composites (porphyrin, zinc oxide nanoparticles, reduced graphene oxide) on a semiconducting electrode without impairing the respective donor-acceptor components. The hierarchical electron transfer cascade system exhibited remarkably high photocurrent generation with an incident-photon-to-current efficiency of up to ca. 70%.

• Carbon nanotube wiring of donor-acceptor nanograins by self-assembly and efficient charge transport.

  Authors: Tomokazu Umeyama, Noriyasu Tezuka, Fumiaki Kawashima, Shu Seki, Yoshihiro Matano, Yoshihide Nakao, Tetsuya Shishido, Masayuki Nishi, Kazuyuki Hirao, Heli Lehtivuori, Nikolai V Tkachenko, Helge Lemmetyinen, Hiroshi Imahori

  Angewandte Chemie (International ed. in English). 05/2011; 50(20):4615-9.

• Formation of single-walled carbon nanotube thin films enriched with semiconducting nanotubes and their application in photoelectrochemical devices.

  Authors: Li Wei, Noriyasu Tezuka, Tomokazu Umeyama, Hiroshi Imahori, Yuan Chen

  Nanoscale. 03/2011; 3(4):1845-9.

  Single-walled carbon nanotube (SWCNT) thin films, containing a high-density of semiconducting nanotubes, were obtained by a gel-centrifugation method. The agarose gel concentration and centrifugationSingle-walled carbon nanotube (SWCNT) thin films, containing a high-density of semiconducting nanotubes, were obtained by a gel-centrifugation method. The agarose gel concentration and centrifugation force were optimized to achieve high semiconducting and metallic nanotube separation efficiency at 0.1 wt% agarose gel and 18,000g. The thickness of SWCNT films can be precisely controlled from 65 to 260 nm with adjustable transparency. These SWCNT films were applied in photoelectrochemical devices. Photocurrents generated by semiconducting SWCNT enriched films are 15-35% higher than those by unsorted SWCNT films. This is because of reducing exciton recombination channels as a result of the removal of metallic nanotubes. Thinner films generate higher photocurrents because charge carriers have less chances going in metallic nanotubes for recombination, before they can reach electrodes. Developing more scalable and selective methods for high purity semiconducting SWCNTs is important to further improve the photocurrent generation efficiency by using SWCNT-based photoelectrochemical devices.

• J-aggregation of a sulfonated amphiphilic porphyrin at the air-water interface as a function of pH.

  Authors: Gustavo de Miguel, Kohei Hosomizu, Tomokazu Umeyama, Yoshihiro Matano, Hiroshi Imahori, Marta Pérez-Morales, María T Martín-Romero, Luis Camacho

  Journal of colloid and interface science. 01/2011; 356(2):775-82.

  π-A isotherms, ellipsometric measurements, Brewster angle microscopy (BAM) and reflection spectroscopy have been utilized to characterize the films of an amphiphilic porphyrin ((OD)(3)TPPS(3)) at theπ-A isotherms, ellipsometric measurements, Brewster angle microscopy (BAM) and reflection spectroscopy have been utilized to characterize the films of an amphiphilic porphyrin ((OD)(3)TPPS(3)) at the air-water interface as a function of pH. This porphyrin forms stable mono-molecular layers at such interfaces, and exhibits different J-aggregation as a function of pH. The J-aggregation of (OD)(3)TPPS(3) on neutral pH subphases is notable considering that the nitrogen atoms at the central macrocycle have a pK(a)≈4.9. The type of aggregates at neutral pH is like those detected at pH<4, because the central porphyrin ring is already protonated. However at basic pH the aggregation happens without protonation of the central ring but can be instead controlled by application of the surface pressure. At the air-water interface, (OD)(3)TPPS(3) shows two bands, a red component and a blue component, which have characteristics of non-degenerate linear oscillators being perpendicularly polarized between each other. The spectral behavior observed on subphases at different pHs is qualitatively interpreted by means of exciton coupling theory, assuming that the degenerate transitions attributed to the Soret band are split. Additionally, highly oriented molecular films of these J-aggregates were deposited onto transparent quartz slides.

• Photoinduced charge carrier dynamics of Zn-porphyrin-TiO2 electrodes: the key role of charge recombination for solar cell performance.

  Authors: Hiroshi Imahori, Soonchul Kang, Hironobu Hayashi, Mitsutaka Haruta, Hiroki Kurata, Seiji Isoda, Sophie E Canton, Yingyot Infahsaeng, Arunkumar Kathiravan, Torbjörn Pascher, Pavel Chábera, Arkady P Yartsev, Villy Sundström

  The journal of physical chemistry. A. 10/2010; 115(16):3679-90.

  Time resolved absorption spectroscopy has been used to study photoinduced electron injection and charge recombination in Zn-porphyrin sensitized nanostructured TiO(2) electrodes. The electronTime resolved absorption spectroscopy has been used to study photoinduced electron injection and charge recombination in Zn-porphyrin sensitized nanostructured TiO(2) electrodes. The electron transfer dynamics is correlated to the performance of dye sensitized solar cells based on the same electrodes. We find that the dye/semiconductor binding can be described with a heterogeneous geometry where the Zn-porphyrin molecules are attached to the TiO(2) surface with a distribution of tilt angles. The binding angle determines the porphyrin-semiconductor electron transfer distance and charge transfer occurs through space, rather than through the bridge connecting the porphyrin to the surface. For short sensitization times (1 h), there is a direct correlation between solar cell efficiency and amplitude of the kinetic component due to long-lived conduction band electrons, once variations in light harvesting (surface coverage) have been taken into account. Long sensitization time (12 h) results in decreased solar cell efficiency because of decreased efficiency of electron injection.

• Dispersion of carbon nanotubes by photo- and thermal-responsive polymers containing azobenzene unit in the backbone.

  Authors: Tomokazu Umeyama, Kazuhiro Kawabata, Noriyasu Tezuka, Yoshihiro Matano, Yuji Miyato, Kazumi Matsushige, Masahiko Tsujimoto, Seiji Isoda, Mikio Takano, Hiroshi Imahori

  Chemical communications (Cambridge, England). 08/2010; 46(32):5969-71.

  Photo- and thermal-responsive polymers containing azobenzene units in the main chain have been utilized as removable dispersants for single-walled carbon nanotubes (SWNTs) in organic solvents.Photo- and thermal-responsive polymers containing azobenzene units in the main chain have been utilized as removable dispersants for single-walled carbon nanotubes (SWNTs) in organic solvents. Intermolecular interactions between SWNTs and the polymers are reversibly controllable by tuning the trans-cis composition.

• Synthesis of alpha,alpha'-linked oligophospholes and polyphospholes by using Pd-CuI-promoted Stille-type coupling.

  Authors: Arihiro Saito, Yoshihiro Matano, Hiroshi Imahori

  Organic letters. 06/2010; 12(11):2675-7.

  Palladium-copper-promoted Stille-type cross-coupling reactions between alpha-stannylphospholes and alpha-iodophospholes afforded alpha,alpha'-linked oligophospholes and polyphosphole efficiently. ItPalladium-copper-promoted Stille-type cross-coupling reactions between alpha-stannylphospholes and alpha-iodophospholes afforded alpha,alpha'-linked oligophospholes and polyphosphole efficiently. It has been revealed that the polyphosphole P-oxide possesses an extremely narrow band gap and a high electron-accepting ability as compared to polythiophene.

• Selective formation and efficient photocurrent generation of [70]fullerene-single-walled carbon nanotube composites.

  Authors: Tomokazu Umeyama, Noriyasu Tezuka, Shu Seki, Yoshihiro Matano, Masayuki Nishi, Kazuyuki Hirao, Heli Lehtivuori, Nikolai V Tkachenko, Helge Lemmetyinen, Yoshihide Nakao, Shigeyoshi Sakaki, Hiroshi Imahori

  Advanced materials (Deerfield Beach, Fla.). 04/2010; 22(15):1767-70.

• Remarkable effects of P-perfluorophenyl group on the synthesis of core-modified phosphaporphyrinoids and phosphadithiasapphyrin.

  Authors: Takashi Nakabuchi, Yoshihiro Matano, Hiroshi Imahori

  Organic letters. 02/2010; 12(5):1112-5.

  P,X,N(2)-type phosphaporphyrins and phosphacalixphyrins (X = N, S) bearing a perfluorophenyl (C(6)F(5)) group at the core phosphorus atom were prepared in high overall yield fromP,X,N(2)-type phosphaporphyrins and phosphacalixphyrins (X = N, S) bearing a perfluorophenyl (C(6)F(5)) group at the core phosphorus atom were prepared in high overall yield from 1-perfluorophenyl-2,5-di(ethoxycarbonyl)phosphole as a common starting material. In addition, P-C(6)F(5) P,S(2),N(2)-type sapphyrin was successfully prepared as the first example of ring-expanded phosphorus-containing porphyrin.

• Good solvent effects of C70 cluster formations and their electron-transporting and photoelectrochemical properties.

  Authors: Noriyasu Tezuka, Tomokazu Umeyama, Yoshihiro Matano, Tetsuya Shishido, Mitsuo Kawasaki, Masayuki Nishi, Kazuyuki Hirao, Heli Lehtivuori, Nikolai V Tkachenko, Helge Lemmetyinen, Yoshihito Honsho, Shu Seki, Hiroshi Imahori

  The journal of physical chemistry. B. 02/2010; 114(45):14287-97.

  Good solvent effects of C(70) cluster formations and their electron-transporting and photoelectrochemical properties have been systematically examined for the first time. Nano-to-micrometer scaleGood solvent effects of C(70) cluster formations and their electron-transporting and photoelectrochemical properties have been systematically examined for the first time. Nano-to-micrometer scale assemblies of C(70) with different morphologies were prepared by rapidly injecting poor solvent (i.e., acetonitrile) into a solution of C(70) dissolved in various good solvents (i.e., benzene, toluene, chlorobenzene, etc). The cluster morphology engineering was successfully achieved by changing the good solvent, yielding the spherical, rodlike, or platelike clusters in the mixed solvents. The clusters of C(70) were electrophoretically deposited onto a nanostructured SnO(2) electrode to examine the photoelectrochemical properties under the white light or monochromatic light illumination. The maximum incident photon-to-current efficiency (IPCE) varied from 0.8 to 10% depending on the combinations of the poor-good solvents. The differences in the IPCE values are discussed in terms of the surface area, thickness, and electron mobility of the deposited cluster films. The electron mobility is found to be the most predominant factor for the IPCE, indicating the importance of the electron-transporting process in the overall photocurrent generation. In addition, the electron mobility is closely correlated with the underlying molecular alignment and the resultant cluster structure. Thus, these results will provide basic clue for the design of C(70)-based molecular devices including the organic photovoltaics.

• Synthesis and Reactions of Phosphaporphyrins: Reconstruction of pi-Skeleton Triggered by Oxygenation of a Core Phosphorus Atom.

  Authors: Takashi Nakabuchi, Makoto Nakashima, Shinya Fujishige, Haruyuki Nakano, Yoshihiro Matano, Hiroshi Imahori

  The Journal of organic chemistry. 12/2009;

  The synthesis, structures, optical and redox properties, and reactivity of phosphaporphyrins are reported. The 21-phosphaporphyrin (P,N(3)-porphyrin) and 23-phospha-21-thiaporphyrinThe synthesis, structures, optical and redox properties, and reactivity of phosphaporphyrins are reported. The 21-phosphaporphyrin (P,N(3)-porphyrin) and 23-phospha-21-thiaporphyrin (P,S,N(2)-porphyrin) were prepared via acid-promoted dehydrative condensation between a phosphatripyrrane and the corresponding 2,5-bis[hydroxy(phenyl)methyl]heteroles followed by 2,3-dichloro-5,6-dicyanobenzoquinone oxidation. Experimental (NMR, UV-vis, and X-ray analyses) and theoretical (DFT calculations) results suggest that the 18pi aromaticity inherent in regular N(4)-porphyrins was maintained in these phosphaporphyrins. X-ray crystallography revealed a slightly distorted 18pi aromatic ring for the P,N(3)-porphyrin with the phosphole and three pyrrole rings tilted from the 24-atoms mean plane by 9.6 degrees and 3.8-15.4 degrees , respectively. DFT calculations on model compounds showed that the P,X,N(2)-porphyrins (X = N, S) possess considerably small HOMO-LUMO gaps as compared with N(4)- and S,N(3)-porphyrins, which is reflected in the red-shifted absorptions, low oxidation potentials, and high reduction potentials of the phosphaporphyrins. The P-oxygenation of the P,X,N(2)-porphyrins with H(2)O(2) has been found to lead to the formation of different types of products. The 18pi P,N(3)-porphyrin was transformed into the 22pi aromatic P(O),N(3)-porphyrin accompanied by the pi extension at the peripheral C(3) bridge, whereas the 18pi P,S,N(2)-porphyrin was converted to the isophlorin-type 20pi antiaromatic P(O),S,N(2)-porphyrin. In both of the reactions, simple P-oxygenated 18pi P(O),X,N(2)-porphyrins were formed as the initial products, which were subsequently transformed into the 22pi or 20pi porphyrins. The two reaction courses from 18pi to 20pi/22pi are apparently determined by the combination of the core heteroatoms (i.e., P,N(3) or P,S,N(2)) and the structure of the peripherally fused carbocycles. The present results demonstrate that the incorporation of a phosphorus atom into the core is not only a highly promising way to modify the fundamental properties of the porphyrin 18pi system but also a reliable tool to stabilize uncommon 22pi and 20pi systems through the chemical modifications at the core phosphorus atom.