Hayao Kobayashi

Bio: Hayao Kobayashi is an academic researcher from Toho University. The author has contributed to research in topics: Magnetoresistance & Electrical resistivity and conductivity. The author has an hindex of 29, co-authored 165 publications receiving 3074 citations.

Magnetotransport Phenomena of α-Type (BEDT–TTF) 2 I 3 under High Pressures

Abstract: The magnetotransport phenomenon is investigated in α-type crystals of (BEDT-TTF) 2 I 3 which are metallized by applying quasi-hydrostatic pressures. At liquid helium temperatures, a fairly large magnetoresistance which rises in very low field and saturates above 0.5 T is observed. The effect of the magnetic field of 1.2 T is found to be recognizable at temperatures above 50 K. Our interpretation of the phenomenon is that the metal-insulator transition which has been suppressed by the pressure arises again, aided by the magnetic field.

Electrical conductivity, thermoelectric power, and ESR of a new family of molecular conductors, dicyanoquinonediimine-metal [(DCNQI) 2 M] compounds

Abstract: A new family of organic molecules, 2-${R}_{1}$-5-${R}_{2}$-DCNQI (with ${R}_{1}$,${R}_{2}$=${\mathrm{CH}}_{3}$, ${\mathrm{CH}}_{3}$O, Cl, or Br; DCNQI=N,N'-dicyanoquinonediimine) works as a ligand as well as an electron acceptor to form highly conducting, charge-transfer and coordination compounds as (2-${R}_{1}$-5-${R}_{2}$-DCNQI${)}_{2}$M (with M=Cu, Ag, Li, Na, K, or ${\mathrm{NH}}_{4}$) These salts are investigated by the measurements of electrical conductivity, thermoelectric power, and electron spin resonance, which are appropriately understood by classifying them into three groups Group-I DCNQI salts consisting of the salts with cations M other than Cu, undergo the Peierls transitions between 50 and 100 K Their thermoelectric power is interpreted by the large-U limit of the Hubbard model Group-II DCNQI salts, the Cu salts of the halogen-substituted DCNQI, also exhibit the Peierls transitions between 150 and 250 K, followed by the antiferromagnetic transitions around 10 K With the one-dimensional tight-binding approximation, the bandwidth is estimated to be 04--05 eV Group-III DCNQI salts, the Cu salts with ${R}_{1}$=${R}_{2}$=${\mathrm{CH}}_{3}$ or ${\mathrm{CH}}_{3}$O retain metallic conductivity down to 15 K, whereas a magnetic transition takes place at 55 K This may be the first organic conductor in which metallic conduction and a magnetic order coexist The magnetic order is attributed to the comparatively localized ${\mathrm{Cu}}^{2+}$ spins present independently of the conduction electrons on DCNQI, where the average oxidation state of Cu has been estimated to be ${\mathrm{Cu}}^{13+}$ AE

Charge Photogeneration in Organic Solar Cells

Abstract: In recent years, organic solar cells utilizing π-conjugated polymers have attracted widespread interest in both the academic and, increasingly, the commercial communities. These polymers are promising in terms of their electronic properties, low cost, versatility of functionalization, thin film flexibility, and ease of processing. These factors indicate that organic solar cells, although currently producing relatively low power conversion efficiencies (∼5-7%),1–3 compared to inorganic solar cells, have the potential to compete effectively with alternative solar cell technologies. However, in order for this to be feasible, the efficiencies of organic solar cells need further improvement. This is the focus of extensive studies worldwide. The backbone of a π-conjugated polymer is comprised of a linear series of overlapping pz orbitals that have formed via sp2 hybridization, thereby creating a conjugated chain of delocalized electron density. It is the interaction of these π electrons that dictates the electronic characteristics of the polymer. The energy levels become closely spaced as the delocalization length increases, resulting in a ‘band’ structure somewhat similar to that observed in inorganic solid-state semiconductors. In contrast to the latter, however, the primary photoexcitations in conjugated polymers are bound electron-hole pairs (excitons) rather than free charge carriers; this is largely due to their low dielectric constant and the presence of significant electron-lattice interactions and electron correlation effects.4 In the absence of a mechanism to dissociate the excitons into free charge carriers, the exciton will undergo radiative and nonradiative decay, with a typical exciton lifetime in the range from 100 ps to 1 ns. Achieving efficient charge photogeneration has long been recognized as a vital challenge for molecular-based solar cells. For example, the first organic solar cells were simple single-layer devices based on the pristine polymer and two electrodes of different work function. These devices, based on a Schottky diode structure, resulted in poor photocurrent efficiency.5–7 Relatively efficient photocurrent generation in an organic device was first reported by Tang in 1986,8 employing a vacuum-deposited CuPc/ perylene derivative donor/acceptor bilayer device. The differing electron affinities (and/or ionization potentials) between these two materials created an energy offset at their interface, thereby driving exciton dissociation. However, the efficiency of such bilayer devices is limited by the requirement of exciton diffusion to the donor/acceptor interface, typically requiring film thicknesses less than the optical absorption depth. Organic materials usually exhibit exciton diffusion lengths of ∼10 nm and optical absorption depths of 100 nm, although we note significant progress is now being made with organic materials with exciton diffusion lengths comparable to or exceeding their optical absorption depth.9–12 The observation of ultrafast photoinduced electron transfer13,14 from a conjugated polymer to C60 and the * To whom correspondence should be addressed. E-mail: j.durrant@ imperial.ac.uk. Chem. Rev. 2010, 110, 6736–6767 6736

Magnetic Molecular Conductors

Abstract: 2.2. BETS Salts with Halometalate Anions 5424 3. Magnetic Metals and Semiconductors 5426 3.1. Mononuclear Metal Complexes 5427 3.1.1. Tetrahalometalates 5427 3.1.2. Hexahalo Anions 5431 3.1.3. Pseudohalide-Containing Anions 5431 3.2. Polynuclear Metal Complexes 5433 3.2.1. Dimeric Anions 5433 3.2.2. Polyoxometalate Clusters 5434 3.3. Chain Anions: Maleonitriledithiolates 5439 4. Ferromagnetic Conductors 5441 5. Ferrimagnetic Insulators 5443 6. Conclusions 5445 7. Acknowledgment 5446 8. References 5446

Discrete fulleride anions and fullerenium cations.

Abstract: Chem. Rev. 2000, 100, 1075−1120 Discrete Fulleride Anions and Fullerenium Cations Christopher A. Reed* and Robert D. Bolskar Department of Chemistry, University of CaliforniasRiverside, Riverside, California 92521-0403 Received June 22, 1999 Contents I. Introduction, Scope, and Nomenclature II. Electrochemistry A. Reductive Voltammetry B. Oxidative Voltammetry III. Synthesis A. Chemical Reduction of Fullerenes to Fullerides i. Metals as Reducing Agents ii. Coordination and Organometallic Compounds as Reducing Agents iii. Organic/Other Reducing Agents B. Electrosynthesis of Fullerides C. Chemical Oxidation of Fullerenes to Fullerenium Cations IV. Electronic (NIR) Spectroscopy A. Introduction B. C 60 n- Fullerides C. C 70 and Higher Fullerenes D. Fullerenium Cations E. Diffuse Interstellar Bands V. Vibrational Spectroscopy A. Infrared Spectroscopy B. Raman Spectroscopy VI. X-ray Crystallography A. Introduction B. [PPN] 2 [C 60 ] and Related C 602- Structures C. C 60 - Structures D. C 603- Structures E. Comparison of Discrete and Extended Structures VII. Magnetic Susceptibility and Spin States VIII. NMR Spectroscopy A. Introduction B. 13 C NMR Data in Solution C. Interpretation of Solution NMR Data D. 13 C NMR Data in the Solid State E. Knight Shift in A 3 C 60 F. 3 He NMR of Endohedral Fullerides G. 13 C NMR of Derivatized Fullerenes H. 13 C NMR of Fullerenium Cations IX. EPR Spectroscopy A. Introduction B. Features of the C 60 - Spectrum i. The Low g Value ii. Temperature Dependence of the Line Width (∆H pp ) X. XI. XII. XIII. iii. Anisotropy iv. Problem of the Sharp Signals v. Origins of Sharp Signals vi. The C 120 O Impurity Postulate vii. The Dimer Postulate C. Features of the C 602- EPR Spectrum D. Features of the C 603- EPR Spectrum E. Features of C 604- and C 605- EPR Spectra F. EPR Spectra of Higher Fullerides G. EPR Spectra of Fullerenium Cations Chemical Reactivity A. Introduction B. Fulleride Basicity C. Fulleride Nucleophilicity/Electron Transfer D. Fullerides as Intermediates E. Fullerides as Catalysts F. Fullerides as Ligands G. Fullerenium Cations Conclusions and Future Directions Acknowledgments References I. Introduction, Scope, and Nomenclature The electron-accepting ability of C 60 , the archetypal fullerene, is its most characteristic chemical property. It is a natural consequence of electronic structure and was anticipated in early molecular orbital calcula- tions 1 which place a low-lying unoccupied t 1u level about 2 eV above the h u HOMO: 2-4 Early in the gas-phase investigations of fullerenes, the electron affinity of C 60 was measured and found to be high (2.69 eV). 5-7 When the macroscopic era of C 60 chemistry began in 1990, this property was soon found to translate into the solution phase. 8 In a rather remarkable cyclic voltammogram (see Figure 1), the reversible stepwise addition of up to six electrons was soon demonstrated electrochemically. 9,10 10.1021/cr980017o CCC: $35.00 © 2000 American Chemical Society Published on Web 02/16/2000

A two-dimensional π–d conjugated coordination polymer with extremely high electrical conductivity and ambipolar transport behaviour

Abstract: Currently, studies on organic two-dimensional (2D) materials with special optic-electronic properties are attracting great research interest. However, 2D organic systems possessing promising electrical transport properties are still rare. Here a highly crystalline thin film of a copper coordination polymer, Cu-BHT (BHT = benzenehexathiol), is prepared via a liquid-liquid interface reaction between BHT/dichloromethane and copper(II) nitrate/H2O. The morphology and structure characterization reveal that this film is piled up by nanosheets of 2D lattice of [Cu-3(C6S6)](n), which is further verified by quantum simulation. Four-probe measurements show that the room temperature conductivity of this material can reach up to 1,580 S cm (-1), which is the highest value ever reported for coordination polymers. Meanwhile, it displays ambipolar charge transport behaviour and extremely high electron and hole mobilities (99 cm(2) V (-1) s (-1) for holes and 116 cm(2) V (-1) s (-1) for electrons) under field-effect modulation.