Yoshio Aso

Osaka University, Suika, Ōsaka, Japan

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Publications (295)860.03 Total impact

  • Asian Journal of Organic Chemistry 02/2013; 2(2):101-101. DOI:10.1002/ajoc.201390003 · 3.32 Impact Factor
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    ABSTRACT: To devise a reliable strategy for achieving specific HOMO and LUMO energy level modulation via alternating donor-acceptor monomer units, we investigate a series of conjugated polymers (CPs) in which the electron withdrawing power of the acceptor group is varied, while maintaining the same donor group and the same conjugated chain conformation. Through experiment and DFT calculations, good correlation is identified between the withdrawing strength of the acceptor group, the HOMO and LUMO levels, and the degree of orbital localization, which allows reliable design principles for CPs. Increasing the acceptor strength results in an enhanced charge transfer upon combination with a donor monomer and a more pronounced decrease of the LUMO level. Moreover, while HOMO states remain delocalized along the polymer chain, LUMO states are strongly localized at specific bonds within the acceptor group. The degree of LUMO localization increases with increasing polymer length, which results in a further drop of the LUMO level and converges to its final value when the number of repeat units reaches the characteristic conjugation length. Based on these insights we designed PBT8PT, which exhibits 6.78% power conversion efficiency after device optimization via the additive assisted annealing, demonstrating the effectiveness of our predictive design approach.
    Advanced Functional Materials 01/2013; 23(4). DOI:10.1002/adfm.201201385 · 11.81 Impact Factor
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    ABSTRACT: New π-conjugated polymers containing difluorodioxocyclopentene-annelated thiophenes as an electron-accepting unit have been synthesized for application to p-type organic semiconducting materials in organic photovoltaics. The photophysical and electrochemical properties of these polymers were investigated by UV--vis absorption spectra and cyclic voltammetry measurements. The carrier mobility measurement of the copolymer on organic field-effect transistor devices revealed p-channel behavior. Bulk heterojunction photovoltaic devices made from blends of the polymer and [6,6]-phenyl-C71-butyric acid methyl ester showed moderate photovoltaic characteristics with a power conversion efficiency of 0.77%.
    Japanese Journal of Applied Physics 10/2012; 51(10). DOI:10.1143/JJAP.51.10NC08 · 1.13 Impact Factor
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    ABSTRACT: 4,9-Dihydro-s-indaceno[1,2-b:5,6-b′]dithiazole-4,9-dione (IDD) was designed as a novel electronegative unit, and the π-conjugated compound (2C-TzPhTz) containing it was synthesized as a candidate for air-stable n-type organic field-effect transistor (OFET) materials. Cyclic voltammetry measurements revealed that the IDD unit contributes to lowering the lowest unoccupied molecular orbital (LUMO) energy level. X-ray crystallographic analysis of 2C-TzPhTz showed an almost planar molecular geometry and dense molecular packing, which is advantageous to electron transport. OFETs based on 2C-TzPhTz showed high electron mobility of up to 0.39 cm2 V-1 s-1, which is one of the highest electron mobilities observed among pentacyclic dione-based materials. Top-contact OFET devices showed operating stability and long-term stability under ambient conditions, attributed to the low-lying LUMO energy level and dense packing in the solid state. Furthermore, bottom-contact OFETs also maintained good electron mobility beyond 0.1 cm2 V-1 s-1 under air-exposed conditions. We demonstrated that n-type OFETs are more sensitive to H2O than O2 and found that the acquirement of air stability for the 2C-TzPhTz-based OFET is due to the increased stability against not only O2 but also H2O. All of these results indicate that IDD is a potentially useful building unit for high-performance air-stable n-type semiconducting materials.Keywords: organic field-effect transistor; electron-transporting material; organic electronics; structure−property relationships
    Chemistry of Materials 08/2012; 24(16):3285-3293. DOI:10.1021/cm301985q · 8.35 Impact Factor
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    ABSTRACT: We report the syntheses, structures, photophysical properties, and redox characteristics of donor-acceptor-fused π-systems, namely π-extended thiadiazoles 1-5 fused with thienopyrrole or indole moieties. They were synthesized by the Stille coupling reactions followed by the PPh(3)-mediated reductive cyclizations as key steps. X-Ray crystallographic studies showed that isomeric 1b and 2b form significantly different packing from each other, and 1a and 4a afford supramolecular networks via multiple hydrogen bonding with water molecules. Thienopyrrole-fused compounds 1b and 2b displayed bathochromically shifted intramolecular charge-transfer (CT) bands and low oxidation potentials as compared to indole-fused analog 3b and showed moderate to good fluorescence quantum yields (Φ(f)) up to 0.73. In 3b-5b, the introduction of electron-donating substituents in the indole moieties substantially shifts the intramolecular CT absorption maxima bathochromically and leads to the elevation of the HOMO levels. The Φ(f) values of 3-5 (0.04-0.50) were found to be significantly dependent on the substituents in the indole moieties. The OFET properties with 1b and 2b as an active layer were also disclosed.
    The Journal of Organic Chemistry 08/2012; 77(17):7595-606. DOI:10.1021/jo301458m · 4.72 Impact Factor
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    ABSTRACT: A convenient method for the synthesis of tetraalkylanthracenes and -pentacenes by means of ruthenium-catalyzed regioselective C-H alkylation of the corresponding acenequinones was developed. Dialkyldiarylpentacene was also synthesized using chemoselective tandem C-H alkylation/C-O arylation of dimethoxypentacenequinone. It was suggested that a tetraalkylpentacene is stable under air in the dark and possesses an appropriate HOMO level as active material for p-type organic field-effect transistors (OFETs).
    Organic Letters 07/2012; 14(15):3882-5. DOI:10.1021/ol301608m · 6.36 Impact Factor
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    ABSTRACT: New donor–acceptor-type copolymers containing dioxocycloalkene-annelated thiophenes as electron-accepting units have been designed and synthesized for application to p-type organic semiconducting materials in organic photovoltaics. The investigation of their photophysical and electrochemical properties revealed that these copolymers possessed low optical bandgaps (from 1.63 to 1.92 eV) and low-lying HOMO energy levels (from −5.41 to −5.33 eV). Organic field-effect transistor measurements revealed that these copolymers had hole-transporting characteristics with mobilities on the order of 10–7–10–4 cm2 V–1 s–1. The bulk-heterojunction photovoltaic devices fabricated from blends of these copolymers with fullerene derivatives as acceptors showed high power conversion efficiencies of up to 4.87%, with an open-circuit voltage of 0.90 V, a short-circuit current of 11.46 mA cm–2, and a fill factor of 0.48 under air mass 1.5 simulated solar illumination.
    Macromolecules 06/2012; 45(11):4564-4571. DOI:10.1021/ma300742r · 5.80 Impact Factor
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    ABSTRACT: A naphthalenediimide derivative 3a carrying TEMPO radical and azobenzene substituent was found to show photoresponsive magnetic as well as FET properties upon illumination. The alteration of its mobility has also been demonstrated by applying magnetic field and hence the FET characteristics of 3a have been proven to be photo- as well as magneto-responsive.
    Chemistry Letters 02/2012; 41(2):175. DOI:10.1246/cl.2012.175 · 1.23 Impact Factor
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    ABSTRACT: The synthesis of 3-hexylthiophene-based oligothiophenes with a length of approximately 10 nm bearing anchor units at both terminal positions has been accomplished. In addition, we have designed and synthesized completely encapsulated oligothiophenes to investigate single-molecule conductance. Their properties are evaluated by UV–vis absorption spectra and cyclic voltammetry (CV) measurements. The conductance of a single-molecule junction for thiol-introduced oligothiophenes was measured by 10-nm-scale nanogap gold electrodes or modified scanning tunneling microscope (STM) techniques.
    Pure and Applied Chemistry 01/2012; 84(4). DOI:10.1351/PAC-CON-11-10-26 · 2.49 Impact Factor
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    ABSTRACT: Ummantelte Oligothiophene wurden verwendet, um Einzelmolekül-Leitfähigkeiten zu untersuchen. UV/Vis/NIR-Messungen der oxidierten Spezies zeigen die Abwesenheit intermolekularer Wechselwirkungen zwischen den konjugierten Hauptketten. Die Leitfähigkeit eines Einzelmolekülkontakts wurde mithilfe modifizierter STM-Techniken gemessen (siehe Bild), und die Abklingkonstante β wurde zu 1.9 nm−1 bestimmt. SMU=Messgerät.
    Angewandte Chemie International Edition 12/2011; 50(50):11980-4. DOI:10.1002/anie.201104700 · 11.26 Impact Factor
  • Angewandte Chemie 12/2011; 123(50). DOI:10.1002/ange.201106644
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    ABSTRACT: Silver nanowires (AgNWs) surrounded by insulating poly(vinylpyrrolidone) have been synthesized by a polyol process and employed as transparent electrodes. The AgNW transparent electrodes can be fabricated by heat-treatment at about 200 °C which forms connecting junctions between AgNWs. Such a heating process is, however, one of the drawbacks of the fabrication of AgNW electrodes on heat-sensitive substrates. Here it has been demonstrated that the electrical conductivity of AgNW electrodes can be improved by mechanical pressing at 25 MPa for 5 s at room temperature. This simple process results in a low sheet resistance of 8.6 Ω/square and a transparency of 80.0%, equivalent to the properties of the AgNW electrodes heated at 200 °C. This technique makes it possible to fabricate AgNW transparent electrodes on heat-sensitive substrates. The AgNW electrodes on poly(ethylene terephthalate) films exhibited high stability of their electrical conductivities against the repeated bending test. In addition, the surface roughness of the pressed AgNW electrodes is one-third of that of the heat-treated electrode because the AgNW junctions are mechanically compressed. As a result, an organic solar cell fabricated on the pressed AgNW electrodes exhibited a power conversion as much as those fabricated on indium tin oxide electrodes. These findings enable continuous roll-to-roll processing at room temperature, resulting in relatively simple, inexpensive, and scalable processing that is suitable for forthcoming technologies such as organic solar cells, flexible displays, and touch screens.
    Nano Research 12/2011; 4(12). DOI:10.1007/s12274-011-0172-3 · 7.01 Impact Factor
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    Masaru Endou · Yutaka Ie · Yoshio Aso
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    ABSTRACT: Oligothiophenes composed of dioxocyclopenta[c]thiophene bearing bulky bis(di-t-butylphenyl) groups were designed and synthesized to develop molecular wires having electron-transporting characteristics. Their effective conjugation, electron affinity, and encapsulation effects were investigated by photophysical and electrochemical measurements.
    Chemical Communications 11/2011; 48(4):540-2. DOI:10.1039/c1cc14994f · 6.83 Impact Factor
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    ABSTRACT: The transformation of bipolarons into polaron pairs in long oligothiophene dications has been reported by Raman spectroscopy. These polaron-pair dicationic species possess singlet open-shell biradicaloid ground electronic states. The formation of biradical polaron pairs marks the end of the quinoidal stability promoted by the intrinsic proaromatic character. The quinoidal stability in TCNQ oligothiophenes in comparison with dicationic oligothiophenes has been addressed.
    Journal of the American Chemical Society 09/2011; 133(41):16350-3. DOI:10.1021/ja2061903 · 12.11 Impact Factor
  • Masashi Nitani · Yutaka Ie · Hirokazu Tada · Yoshio Aso
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    ABSTRACT: A series of electronegative π-conjugated compounds composed of carbonyl-bridged bithiazole and alkyl-substituted dioxocyclopenta[b]thiophene were synthesized as a candidate for solution-processable n-type organic semiconductor materials and characterized on the basis of photophysical and electrochemical properties. Cyclic voltammetry measurements showed that the first half-wave reduction potentials of these compounds are between -0.97 and -1.14 V versus ferrocene/ferrocenium, which corresponds to lowest unoccupied molecular orbital energy levels between -3.83 and -3.66 eV. Thanks to hexyl or dodecyl groups in the molecules, the compounds are sufficiently soluble to realize the fabrication of their thin films through a spin-coating method. As a result, the prepared organic field-effect transistors based on these newly developed compounds exhibited n-channel characteristics not only under vacuum but also in air, and the best field-effect electron mobility observed under vacuum was 0.011 cm(2) V(-1) s(-1) with an on/off ratio of 10(8) and a threshold voltage of 16 V.
    Chemistry - An Asian Journal 09/2011; 6(9):2352-61. DOI:10.1002/asia.201100098 · 4.59 Impact Factor
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    ABSTRACT: We have synthesized new electron-transporting oligothiophenes containing dicyanomethylene-substituted cyclopenta[b]thiophene as an active material for the fabrication of solution-processable n-type organic field-effect transistors (OFETs). The influence of the number of dicyanomethylene groups as well as the position of hexyl groups was investigated in detail by performing photophysical and electrochemical measurements. Results revealed that the optical energy gaps and the lowest unoccupied molecular orbital (LUMO) energy levels can be controlled by changing the number of dicyanomethylene groups. In contrast, the position of hexyl groups has little influence on molecular electronic properties. X-ray diffraction and atomic force microscopy measurements revealed that spin-coated thin films of the new compounds had a crystalline structure. OFETs based on these compounds were evaluated in vacuum and air-exposed conditions, and the electron mobility of up to 0.016 cm(2) V(-1) s(-1) was achieved. Furthermore, we demonstrated that the air stability of the OFETs depends on the LUMO energy level of the compounds.
    The Journal of Organic Chemistry 08/2011; 76(16):6604-10. DOI:10.1021/jo200890b · 4.72 Impact Factor
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    ABSTRACT: A new convenient method for the synthesis of dibenzo[a,h]anthracenes and picenes using ruthenium-catalyzed regioselective C-H arylation of aromatic ketones has been developed. Acetophenone derivatives and 1,4-benzenediboronates were coupled in 2:1 ratios to form p-terphenyl derivatives. Conversion of the acetyl group to an ethynyl group, followed by cycloaromatization provided the desired fused aromatic compounds. An organic field-effect transistor fabricated from one of these products gave moderate hole mobility.
    ChemInform 08/2011; 42(33). DOI:10.1002/chin.201133085
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    ABSTRACT: Solution-processable, electronegative, π-conjugated systems containing dicyanomethylene-substituted cyclopenta[b]thiophene were synthesized as potential active materials for air-stable n-type organic field-effect transistors (OFETs). Electrochemical measurements revealed that these compounds exhibited electrochemical stability and that the lowest unoccupied molecular orbital (LUMO) had an energy level less than -4.0 eV. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements were performed, and the value of intradomain electron mobility was determined to be as high as 0.1 cm(2) V(-1) s(-1) . The OFETs were fabricated by spin-coating thin films of the compounds as an active layer. The electron mobility of the OFETs was 3.5×10(-3) cm(2) V(-1) s(-1) in vacuum. Furthermore, electron mobility of the same order of magnitude and stable characteristics were obtained under air-exposed conditions. X-ray diffraction measurements of the spin-coated thin films revealed the difference of molecular arrangements depending on the inner conjugated units. Atomic force microscopy measurements of crystalline-structured films exhibited the formation of grains. The accomplishment of air-stability was attributed to the combined effect of the low-lying LUMO energy level and the molecular arrangements in the solid state, avoiding both the quenching of electron carriers and the intrusion of oxygen and/or moisture.
    Chemistry - A European Journal 04/2011; 17(17):4750-8. DOI:10.1002/chem.201002995 · 5.73 Impact Factor
  • Makoto Karakawa · Yutaka Ie · Yoshio Aso
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    ABSTRACT: We have designed and synthesized new polymer semiconductors containing branched oligothiophene units. These polymers form amorphous films with high thermal stability owing to strong interactions between oligothiophene side chains. On thin-film devices fabricated by spin coating of these polymers as a semiconducting layer, the field-effect mobility increased from 10−6 to 10−4 cm2 V−1 s−1 with increasing side-chain length. The UV–vis absorption, photoluminescence and electrochemical properties of the polymers in solutions were also affected by the length of the side chains.
    Semiconductor Science and Technology 02/2011; 26(3):034004. DOI:10.1088/0268-1242/26/3/034004 · 2.19 Impact Factor
  • Tomoya Hirose · Yutaka Ie · Yoshio Aso
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    ABSTRACT: Synthesis of new tripodal-anchor units composed of a tetraphenylmethane core with pyridine or amine as anchoring functional groups has been successfully accomplished. Cyclic voltammetry measurements of their monolayers on metal electrodes revealed the estimated surface coverage and robust adsorption of three-armed structures on the surface.
    Chemistry Letters 02/2011; 40(2):204-205. DOI:10.1246/cl.2011.204 · 1.23 Impact Factor

Publication Stats

4k Citations
860.03 Total Impact Points


  • 2000–2015
    • Osaka University
      • Institute of Scientific and Industrial Research
      Suika, Ōsaka, Japan
  • 2011–2012
    • Keio University
      • Department of Chemistry
      Edo, Tōkyō, Japan
  • 1984–2010
    • Hiroshima University
      • • Department of Applied Chemistry
      • • Graduate School of Engineering
      Hirosima, Hiroshima, Japan
  • 2005
    • Japan Science and Technology Agency (JST)
      Edo, Tōkyō, Japan
  • 2001
    • Tohoku University
      • Institute of Multidisciplinary Research for Advanced Materials (IMRAM)
      Miyagi, Japan
  • 1999–2000
    • Kyushu University
      Hukuoka, Fukuoka, Japan
    • Fukuoka University
      Hukuoka, Fukuoka, Japan
  • 1989
    • Nagoya University
      • Department of Chemistry
      Nagoya, Aichi, Japan