田島 裕之

20-μm-diameter WGM resonators that include a terfluorene emission layer and a 10-nm-thick layer of Al or Ag were investigated. The plasmon-quenching effect on amplified spontaneous emission was effectively suppressed by the resonator structure.

We developed a device parameter to evaluate the magnitude of the energy transfer in organic WGM resonators. ASE easily occurs under the condition that the energy acceptor molecules become unable to accept energy from the energy donor excitons.

We report the synthesis of P-BT and TP-BT and their OTFT properties based on electronic dimensionality and access resistance (R_acc). TP-BT can suppress R_acc due to its 3D electronic structure.

Accumulated charge measurement (ACM) is an experimental technique for studying the charge-injection and extraction processes in a condenser comprising the following: metal electrode 1, insulator (INS), organic semiconductor (OS), and metal electrode 2 (M2). In this method, the change in the accumulated charge (Q(acc)) is estimated by integrating the displacement current when the applied voltage changes from V-off to V-off + V-a. V-off is the constant offset voltage and V-a is the alternating voltage that is changed step-by-step; Q(acc) is expressed as a function V-a. From the observed dataset of Q(acc) and V-a, & UDelta;Q and V-OS are derived, where & UDelta;Q is the degree of charge injection and V-OS is the voltage drop within the OS layer caused by V-a. The injection barrier at the OS/M2 interface can be evaluated from the plot of & UDelta;Q as a function of V-OS. In this study, two theoretical models for analyzing ACM data are developed using the Poisson-Boltzmann equation. On the one hand, the thermal equilibrium (TE) model reflects the TE process, in which charge evacuation simultaneously occurs at the INS/OS and OS/M2 boundaries. On the other hand, the non-thermal equilibrium (NTE) model assumes a two-step charge evacuation process at the interfaces: charge evacuation at the OS/M2 boundary occurs in the first step, followed by charge evacuation at the INS/OS boundary in the second step. The ACM data for condensers constituting pentacene and H2Pc are well reproduced by the TE and NTE models, respectively. The different behaviors of the two condensers can be attributed to the difference in their diffusion constants.

This study investigates the charge injection barrier at the phthalocyanine (H2Pc)/Pd using accumulated charge measurement (ACM). Because the hole injection barrier is relatively small, the voltage oscillation method in ACM is achieved at the highest occupied molecular orbital/Pd interface, and the hole injection barrier was determined to be 0.26 eV. A negative offset voltage was applied to determine the electron injection barrier at the lowest unoccupied molecular orbital (LUMO)/Pd interface. However, when the electron injection barrier was significantly large, the charge-injected thermal equilibrium state (CITES) could not be achieved at the interface, and an accurate injection barrier could not be determined. Surprisingly, by applying a positive offset voltage, a CITES of electrons was obtained at the LUMO/Pd interface, and the band gap was determined to be 2.75 eV. Furthermore, the electron injection barrier was found to be 2.49 eV. By applying a positive offset voltage, band bending occurred at the H2Pc/Pd interface, thereby reducing the depletion layer in the LUMO and enabling the determination of the band gap and electron injection barrier.

Chemical modification of insulating material surfaces is an important methodology to improve the performance of organic field-effect transistors (OFETs). However, few redox-active self-assembled monolayers (SAMs) have been constructed on gate insulator film surfaces, in contrast to the numerous SAMs formed on many types of conducting electrodes. In this study, we report a new approach to introduce a Ï-conjugated organic fragment in close proximity to an insulating material surface via a transition metal center acting as a one-atom anchor. On the basis of the reported coordination chemistry of a catecholato complex of Pt(II) in solution, we demonstrate that ligand exchange can occur on an insulating material surface, affording SAMs on the SiO2 surface derived from a newly synthesized Pt(II) complex containing a benzothienobenzothiophene (BTBT) framework in the catecholato ligand. The resultant SAMs were characterized in detail by water contact angle measurements, X-ray photoelectron spectroscopy, atomic force microscopy, and cyclic voltammetry. The SAMs served as good scaffolds of Ï-conjugated pillars for forming thin films of a well-known organic semiconductor C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), accompanied by the engagements of the C8-BTBT molecules with the SAMs containing the common BTBT framework at the first layer on SiO2. OFETs containing the SAMs displayed improved performance in terms of hole mobility and onset voltage, presumably because of the unique interfacial structure between the organic semiconducting and inorganic insulating layers. These findings provide important insight into creating new elaborate interfaces through installing coordination chemistry in solution to solid surfaces, as well as OFET design by considering the compatibility between SAMs and organic semiconductors.

A silane coupling-based procedure for decoration of an insulator surface containing abundant hydroxy groups by constructing redox-active self-assembled monolayers (SAMs) is described. A newly synthesized ferrocene (Fc) derivative containing a triethoxysilyl group designated FcSi was immobilized on SiO2/Si by a simple operation that involved immersing the substrate in a toluene solution of the Fc silane coupling reagent and then rinsing the resulting substrate. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the Fc group was immobilized on SiO2/Si in the Fe(II) state. Cyclic voltammetry measurements showed that the Fc groups were electrically insulated from the Si electrode by the SiO2 layer. The FcSi on SiO2/Si structures were found to serve as a good scaffold for formation of organic semiconductor thin films by vacuum thermal evaporation of C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), which is well-known as an organic field-effect transistor (OFET) material. The X-ray diffraction profile indicated that the conventional standing-up conformation of the C8-BTBT molecules perpendicular to the substrates was maintained in the thin films formed on FcSi@SiO2/Si. Further vacuum thermal evaporation of Au provided an FcSi-based OFET structure with good transfer characteristics. The FcSi-based OFET showed pronounced source-drain current hysteresis between the forward and backward scans. The degree of this hysteresis was varied reversibly via gate bias manipulation, which was presumably accompanied by trapping and detrapping of hole carriers at the Fc-decorated SiO2 surface. These findings provide new insights into application of redox-active SAMs to nonvolatile OFET memories while also creating new interfaces through junctions with functional thin films, in which the underlying redox-active SAMs play supporting roles.

We report a crystal structure analysis of an unsymmetrical organic semiconductor 2-bromo-7-butyl[1]benzothieno[3,2-b][1]benzothiophene (Br-BTBT-C ) and its transistor characteristics. Unlike the parent compound 2-butyl-[1]benzothieno[3,2-b][1]benzothiophene (BTBT-C ) forming a bilayer-type structure composed of head-to-head herringbone packings, Br-BTBT-C forms a dense head-to-tail herringbone packing arranged so as to avoid the steric hindrance between bromine atoms. The intermolecular transfer integrals in Br-BTBT-C suggest its advantage for carrier transport; however, the transistor characteristics of Br-BTBT-C and BTBT-C were found to be almost the same. This is because BTBT-C has a higher crystallinity than Br-BTBT-C in vacuum deposited thin films. 4 4 4 4 4 4 4 4

Accumulated charge measurement (ACM) is a new experimental technique for organic semiconductors to evaluate the charge injection barrier at the semiconductor–metal interface directly using a metal–insulator–semiconductor–metal (MISM) capacitor. In this technique, the precise estimation of the electrostatic capacity of the insulator layer (C ) is required for the analysis. The information of this parameter is, in principle, included in the ACM data; however, it is not directly evaluated because of the error resulting from the charge-spreading effect in an organic MISM capacitor with an unrestricted electrode structure. Therefore, the C in previous ACM experiments has been independently estimated from the area of the electrode. In this study, a novel design of a substrate with a restricted-bottom-electrode structure is reported. Using the newly designed substrate, it was possible to suppress the charge-spreading effect and successfully estimate precise values of C directly from the ACM data. Subsequently, it was possible to evaluate the injection barriers at the metal-free phthalocyanine (H Pc)–Ag and pentacene–Au interfaces, which were 0.4 and 0.15 eV, respectively. The built-in potentials in the semiconductor layer were also determined for the samples used in the measurement. I I I 2

Hole injection barriers at the regioregular-poly-3(hexylthiophene) (RR-P3HT)/metal (Cu or Ag) interface were investigated using the accumulated charge measurement (ACM). Thermal annealing of RR-P3HT at 55 °C decreased the injection barrier. RR-P3HT thermally annealed in N forms an ohmic contact with Ag and a Schottky contact with Cu. The obtained values of the injection barriers, ϕ were well expressed by the Mott-Schottky rule, i.e., ϕ = IE - W ′, where IE is the ionization energy of RR-P3HT and W ′ is the work function of the metal electrode in air. The effect of the large vacuum level shift, reported in UPS studies conducted under ultrahigh vacuum, was not observed. 2 B B m m

We have investigated the magnetic properties of TPP[Mn(Pc)(CN)2]2 by the cantilever magnetometry technique. This technique enables us to extract information on the magnetism even if the sample is very small (1 μg). The torque curve measured when the magnetic field (≤7 T) is rotated in a plane that includes the c-axis shows a signature that is characteristic of weak ferromagnetism. The electron responsible for this behavior should be the d electron of the Mn ion. On the other hand, when the field is rotated in the ab-plane, the torque curve exhibits an antiferromagnetic signature. The electron responsible for this behavior should be the π electron. Taking the susceptibility data into account, we have proposed two models of the spin configuration for d electrons: canted antiferromagnetism, and the field-induced ferromagnetic alignment. We have pointed out that even in the canted antiferromagnetic case, the torque curve is the same as that in the ferromagnetic case if the anisotropy energy is very small. These models do not contradict the experimental observation that magnetoresistance is hardly seen in TPP[Mn(Pc)(CN) ] if the interaction between π and d electrons is weak. 3+ 2 2

The effect of the offset bias voltage on the threshold voltage of the hole injection into the organic-semiconductor (OS) layer was examined in detail in the accumulated charge measurement (ACM) for the n-type Si/SiO /OS/Ag (OS = zinc phthalocyanine [ZnPc] or metal-free phthalocyanine [H Pc]) capacitor. The threshold highly depends on the offset bias voltages, when the OS layer is in the hole-depletion regime. On the contrary, the threshold was nearly constant when the OS layer operated in the hole-accumulation regime. The hole injection barrier of the Ag/OS interface was obtained by the threshold in the accumulation regime. The obtained values were 0.41 and 0.05 eV for H Pc/Ag and ZnPc/Ag interfaces, respectively. The study revealed that accurate estimation of the injection barrier is possible by examining the offset voltage dependence in the ACM. 2 2 2

The optical properties of ternary type-I Ge clathrate Ba Ga Ge are investigated by optical reflectance and transmittance measurements. The refractive index and extinction coefficient are calculated from the reflectance spectrum via the modified Kramers-Kronig analysis method between 0.5 and 3.2 eV. The photon energy dependence of the optical absorption coefficient reveals that Ba Ga Ge is an indirect band gap semiconductor with a gap energy E of 0.69 eV at 5.7 K and 0.66 eV at 285 K. The temperature dependence of E can be satisfactorily described by an equation based on the Bose-Einstein statistics model. When compared with those of common elemental, III-V, and II-VI semiconductors, the small temperature coefficient dE /dT of the Ba Ga Ge can be considered to represent the weak electron-phonon interaction in the Ba Ga Ge clathrate. 8 16 30 8 16 30 g g g 8 16 30 8 16 30

A conducting molecular crystal TPP[Mn (Pc)(CN) ] (Mn : d , S = 1, TPP = tetraphenylphosphonium and Pc = phthalocyanine) was fabricated. In its crystal structure, the [Mn (Pc)(CN) ] units formed a one-dimensional regular chain along the c-axis with an overlap integral value of 8.6 × 10 . TPP[Mn (Pc)(CN) ] showed a semiconducting behaviour that also has been observed for isostructural TPP[Co (Pc)(CN) ] (Co : d , S = 0) and TPP[Fe (Pc)(CN) ] (Fe : d , S = 1/2) whose ground states are charge-ordered states. In spite of the local magnetic moment of the Mn ion (S = 1) at the centre of the Pc ligand, TPP[Mn (Pc)(CN) ] exhibited an almost isotropic and small negative magnetoresistance (MR) effect (the MR ratio was −8.7% under 8 T at 10.7 K), contrarily to the anisotropic giant negative MR effect of TPP[Fe (Pc)(CN) ] . The isotropy was found to be due to a (d ) (d ) electronic configuration, and the smaller MR effect was explained by a weaker antiferromagnetic interaction between Mn ions than that between Fe ions, as suggested by a Weiss temperature Θ of −3.1 K (|J |/k = 1.2 K). III III 4 III −3 III III III 6 III III 5 III III III 1 1 III III 2 2 2 2 2 2 2 2 2 2 2 2 2 xz yz dd B

A new technique to determine the injection barrier using displacement current measurement (DCM) is reported. This technique was applied to junctions of metal-free phthalocyanine (H Pc)/Ag and H Pc/MoO /Ag. The injection barriers from Ag to the highest occupied molecular orbital of H Pc and to the lowest unoccupied molecular orbital of H Pc were evaluated and found to be 0.4 V and 1.8 V, respectively. No barrier was formed for the hole injection from the MoO /Ag electrode into H Pc. These results are relatively consistent with an energy diagram built on the basis of the ionization energy for H Pc, Ag, and MoO , in addition to the electron affinity for H Pc. 2 2 3 2 2 3 2 2 3 2

We studied the effect of the localized spin concentration on the giant magnetoresistance (GMR) and the charge order (CO) in the phthalocyanine (Pc) molecular conductors TPP[FexCo (Pc)(CN) ] (TPP = tetraphenylphosphonium), in which the localized spin concentration can be controlled by adjusting the Fe concentration x. Resistivity studies indicated that the CO state was stabilized by localized spins. The negative magnetoresistance was observed even in the region of a localized spin concentration of as low as about 5%. In the high-concentration region, the negative magnetoresistance changed into a positive one at low temperatures. This result shows that a magnetic field stabilizes the CO state, unless the magnetic field is sufficiently strong to break the antiferromagnetic order of the localized spins. 1-x 2 2

We report an experimental investigation of the magnetic field effect (MFE) in polymer bulk heterojunction devices at temperatures below 10 K using photocarrier extraction by linearly increasing voltages. The examined devices were composed of an active layer of poly(3-hexylthiophene) and [6,6]-phenyl-C -butyric acid methyl ester. In the experiments, the delay time (t ) dependence of the MFE was investigated in detail. For t < 80 μs, a positive MFE was observed in the field region B < 0.1 T and a negative MFE was observed for B > 0.2 T. For t > 8 ms, only a positive MFE proportional to B was observed. For the photocurrent pulse detected immediately after light irradiation, the MFE was negligibly small. In a high magnetic field of 15 T, a significant MFE exceeding 80% was observed at 1.8 K for t = 800 ms. We discuss the results based on a model of triplet-singlet (or singlet-triplet) conversion in the magnetic field and estimate the exchange integral for the charge-transfer exciton in this photovoltaic cell. 61 d d d d 2

We have investigated the melt growth of Mg Si crystal and its electrical and optical properties. Progress in Mg source purity and stoichiometric control during the growth enabled the development of a high purity Mg Si crystal with low carrier density and a high stable Mg Si with good doping controllability. The Mg Si crystal grown by the pressure controlled Bridgman method using 5N purity or 6N purity of Mg source and purified PG crucible showed low electron density (∼10 cm ) and high electron mobility (485cm V s at 300K and 21900 cm V s at 40 K). Silver doping in the high purity crystals performed the low-hole density of p-type Mg Si (∼3 × 10 cm ). Ionization energy of residual Al donor in the high purity crystal and Ag acceptor in the Ag doped crystals was determined as 8-9meV and 26meV, respectively. Indirect band gap energy E of approximately 0.61 eV at 300K and 0.69 eV at 4K were estimated by the optical transmission measurements on the high purity crystals. It is also found that the Sb-doped melt grown crystal had good power factor around room temperature (26μWcm K at 270 K). 2 2 2 2 2 g 15 -3 2 -1 -1 2 -1 -1 16 -3 -1 -2

We report systematic studies on the spin current transport and relaxation mechanism in thin films of the highly doped organic polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), in which hopping charge transport is dominant. In this study, we determined the spin diffusion length, spin lifetime, and spin diffusion constant using different experimental techniques. The experimentally obtained spin lifetime is much shorter than that of nondoped organic semiconductors. This clearly shows considerable enhancement of spin relaxation in highly doped PEDOT molecules, which form the trapping centers of hopping transport. Also, we obtained a longer spin diffusion length than the average hopping length, indicating that spins are almost conserved during the hopping process. These facts suggest that spin relaxation of this material mainly occurs in the nanograins of the PEDOT molecules.

We report the results of SQUID and torque magnetometry of an organic spin-1/2 triangular-lattice kappa - H(3)dCat-EDT-TTF)(2). Despite antiferromagnetic exchange coupling at 80-100 K, we observed no sign of antiferromagnetic order down to 50 mK owing to spin frustration on the triangular lattice. In addition, we found nearly temperature-independent susceptibility below 3 K associated with Pauli paramagnetism. These observations suggest the development of gapless quantum spin liquid as the ground state. On the basis of a comparative discussion, we point out that the gapless quantum spin liquid states in organic systems share a possible mechanism, namely the formation of a band with a Fermi surface possibly attributed to spinons.

Herein, we report the fabrication of an organic spintronic device by a one-pot process called nanoscale electrocrystallization, that allows for the site-selective growth of organic nanocrystals on a substrate between two electrodes. Axially substituted iron phthalocyanine was used to constitute the nanocrystals that exhibited a strong correlation between the localized spin and conduction electrons. In addition, the nanocrystals exhibited a negative giant magnetoresistance ([R(B) - R(0)]/R(0)) of around -56%. Moreover, the spintronic device exhibited an angular dependence of its negative giant magnetoresistance, which confirmed the highly oriented growth of the nanocrystals by the nanoscale electrocrystallization method. In summary, our method enables the easy fabrication of organic spintronic devices based on such spin interactions. ? 2013 The Royal Society of Chemistry.

Herein, we report the fabrication of an organic spintronic device by a one-pot process called nanoscale electrocrystallization, that allows for the site-selective growth of organic nanocrystals on a substrate between two electrodes. Axially substituted iron phthalocyanine was used to constitute the nanocrystals that exhibited a strong correlation between the localized spin and conduction electrons. In addition, the nanocrystals exhibited a negative giant magnetoresistance ([R(B) - R(0)]/R(0)) of around -56%. Moreover, the spintronic device exhibited an angular dependence of its negative giant magnetoresistance, which confirmed the highly oriented growth of the nanocrystals by the nanoscale electrocrystallization method. In summary, our method enables the easy fabrication of organic spintronic devices based on such spin interactions. © 2013 The Royal Society of Chemistry.

The magnetization and transport properties of iron-phthalocyanine molecular conductors are investigated under pulsed high magnetic fields up to 55 T. The metamagnetic transition is observed at approximately 14 T, where conductivity is enhanced. Below this transition, the tan delta (= epsilon ''/epsilon') in the dielectric constants shows a monotonic decrease as the magnetic field strength increases, indicating that the magnetic field stabilizes the charge order. On the verge of this transition, the dielectric constants show a hysteresis below the weak-ferromagnetic transition temperature (6 K), suggesting that the pi-electron charge order contributes to the weak ferromagnetism.

The effect of electrostatic charge carrier injection into the charge-ordered (CO) organic materials [α-(BEDT-TTF)2I 3 and α′-(BEDT-TTF)2IBr2] using a field effect transistor (FET) structure is investigated. Depending on the devices, both n-type and p-type behaviors are observed. Our results reveal that only the hole transfer property is strongly affected by the interface conditions of the devices. In addition, our devices presently show relatively low gate response compared to the recently reported organic Mott FET. This result suggests that a gate-induced drastic change of electronic state, which is proposed in the organic Mott FET, is not observed in the present CO FET. © 2013 Elsevier B.V. All rights reserved.

We have presented a calibration technique for commercially available atomic force microscopy (AFM) cantilevers used in torque magnetometry experiments. The absolute values (J/rad) of the torque can be derived against the output signal, which is the change in piezoresistivity due to the deflection of the cantilever beam. The calibration has been performed using the susceptibility of a graphite plane. The linearity between the output signal and the torque is confirmed up to +/- 1 x 10(-8) J/rad of the torque. More importantly, since the nonlinear response of the cantilever is reproducible, we have also utilized the nonlinear region, so that the calibration range has been pushed up to +/- 4 x 10(-8) J/rad. In the nonlinear range, an important finding is that any curve (torque vs output signal curve) that is cantilever-dependent reduces to a single universal curve, after multiplying an appropriate factor. This factor is cantilever-dependent, but can be derived by rotating the sample-mounted cantilever in a zero magnetic field. We have also proposed a simple model regarding the presence of this universal curve. (C) 2013 The Japan Society of Applied Physics

The structural, electronic, and optical properties of pyrochlore-type Pb2Ir2O6O0.55′, which is a metal without spatial inversion symmetry at room temperature, were investigated. Structural analysis revealed that the structural distortion relevant to the breakdown of the inversion symmetry is dominated by the Pb-O′ network but is very small in the Ir-O network. At the same time, gigantic second-harmonic generation signals were observed, which can only occur if the local environment of the Ir 5d electrons features broken inversion symmetry. First-principles electronic structure calculations reveal that the underlying mechanism for this phenomenon is the induction of the noncentrosymmetricity in the Ir 5d bands by the strong hybridization with O′ 2p orbitals. Our results stimulate theoretical study of inversion-broken iridates, where exotic quantum states such as a topological insulator and Dirac semimetal are anticipated. © 2013 American Physical Society.

We have measured the magnetic torque of TPP[Fe(Pc)Br<inf>2</inf>]<inf>2</inf>and TPP[Fe(Pc)Cl<inf>2</inf>]<inf>2</inf>to clarify their magnetic state, comparing our results with those of formerly performed experiments on TPP[Fe(Pc)CN<inf>2</inf>]<inf>2</inf>. The conductors in this family exhibit giant negative magnetoresistance. We employed the cantilever magnetometry technique with our newly developed calibration method to obtain absolute values of the torque (J/rad Fe mol), enabling the comparison between experimental and calculated results. With decreasing temperature, the antiferromagnetic ordering of the \pi electron is found to occur at {\sim}13 K, and then the antiferromagnetic short-range ordering of the d electron follows at {\sim}8 K in these two salts. Our anisotropic one-dimensional Heisenberg model can explain 1) the susceptibility data quantitatively, 2) the torque curves quantitatively, which were obtained when the magnetic field was rotated in the ac-plane, and 3) the behavior of the d electron in the torque curves qualitatively, which were obtained by rotating the field in the ab-plane. By combining our model with the antiferromagnetic model for the \pi electron, the experimental torque data on TPP[Fe(Pc)Br<inf>2</inf>]<inf>2</inf>and TPP[Fe(Pc)Cl<inf>2</inf>]<inf>2</inf>are satisfactorily described. In addition, we could also successfully obtain the anisotropy energy in the antiferromagnetic state.

We have measured the magnetic torque of TPP[Fe(Pc)Br-2](2) and TPP[Fe(Pc)Cl-2](2) to clarify their magnetic state, comparing our results with those of formerly performed experiments on TPP[Fe(Pc)CN2](2). The conductors in this family exhibit giant negative magnetoresistance. We employed the cantilever magnetometry technique with our newly developed calibration method to obtain absolute values of the torque (J/rad Fe mol), enabling the comparison between experimental and calculated results. With decreasing temperature, the antiferromagnetic ordering of the pi electron is found to occur at similar to 13 K, and then the antiferromagnetic short-range ordering of the d electron follows at similar to 8 K in these two salts. Our anisotropic one-dimensional Heisenberg model can explain 1) the susceptibility data quantitatively, 2) the torque curves quantitatively, which were obtained when the magnetic field was rotated in the ac-plane, and 3) the behavior of the d electron in the torque curves qualitatively, which were obtained by rotating the field in the ab-plane. By combining our model with the antiferromagnetic model for the pi electron, the experimental torque data on TPP[Fe(Pc)Br-2](2) and TPP[Fe(Pc)Cl-2](2) are satisfactorily described. In addition, we could also successfully obtain the anisotropy energy in the antiferromagnetic state.

Nanocrystalline films of phthalocyanine-based molecular conductors were fabricated using a short-time electrocrystallization method with two indium-tin oxide (ITO) electrodes. The size and morphology of the nanocrystals could be controlled by adjusting the electrocrystallization conditions, and the ITO substrate was successfully covered with nanocrystals of the molecular conductor. The current density versus voltage (J-V) characteristics of devices with the configuration ITO/nanocrystals:C-60/Al showed a reverse rectifying effect accompanied by a photovoltaic effect under 660nm wavelength irradiation, which is close to the gap between the HOMO and LUMO of phthalocyanine. (C) 2013 The Japan Society of Applied Physics

Two organic light-emitting devices (OLEDs) were fabricated to investigate the mechanism of electroluminescence (EL) switching accompanying the spin transition of [Fe(dpp)2](BF4)2 (dpp = 2,6-di(pyrazol-1-yl)pyridine) observed in an OLED with the structure indium tin oxide (ITO)/[Fe(dpp)2](BF4)2:chlorophyll a/Al, consisting of a chlorophyll a (Chl a)-doped [Fe(dpp)2](BF 4)2 film. One OLED consisted of poly(N-vinylcarbazole) (PVK) between an ITO electrode and the active layer, and the other contained the electron transporting dye Nile Red (NR) as an emitting dopant material instead of the hole transporting Chl a. In both devices ITO/PVK/[Fe(dpp) 2](BF4)2:Chl a/Al and ITO/[Fe(dpp) 2](BF4)2:NR/Al, EL emission from the dye compound was observed, irrespective of the spin state of [Fe(dpp) 2](BF4)2. It was determined that the EL switching accompanying the spin transition was dominated by a change in the molecular orbital level concerning electron transport in [Fe(dpp) 2](BF4)2. © 2013 Elsevier B.V.

The metallic state of the molecular conductor beta-(meso-DMBEDT-TTF)(2)X (DMBEDT-TTF = 2-(5,6-dihydro-1,3-dithiolo[4,5-b][1,4] dithiin-2-ylidene)-5,6-dihydro5,6-dimethyl-1,3-dithiolo[4,5-b][1,4]dithiin, X = PF6, AsF6) is transformed into the checkerboard-type charge-ordered state at around 75-80 K with accompanying metal-insulator (MI) transition on the anisotropic triangular lattice. With lowering temperatures, the magnetic susceptibility decreases gradually and reveals a sudden drop at the MI transition. By applying pressure, the charge-ordered state is suppressed and superconductivity appears in beta-(meso-DMBEDT-TTF)(2)AsF6 as well as in the reported beta-(meso-DMBEDT-TTF)(2)PF6. The charge-ordered spin-gapped state and the pressure-induced superconducting state are discussed through the paired-electron crystal (PEC) model, where the spin-bonded electron pairs stay and become mobile in the crystal, namely the valence-bond solid (VBS) and the resonant valence bonded (RVB) state in the quarter-filled band structure.

Photoinduced charge carrier extraction experiments using a linearly increasing voltage (photo-CELIV) are reported for an organic thin film device from 1.8 to 150 K. This device is composed of an active layer of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM). Photo-CELIV data for a zigzag shape voltage sweep provide critical evidence that the CELIV signal reflects the evacuation of charged carriers captured by traps under a high electric field. The data are analyzed using the Poole-Frenkel model. The trap density as a function of escape energy is obtained as rho(epsilon) = D exp{-(epsilon - epsilon(0))(2)/sigma(2)}, with D = 1.0 x 10(24) states m(-3) eV(-1), epsilon(0) = 0.087 eV, and sigma = 0.029 eV. The carrier drift mobility is estimated to be 2.3 x 10(-6) cm(2) V-1 s(-1) at 1.8 K. As inferred from the light intensity dependence of the photo-CELIV data, geminate pairs are proposed as the origin of traps. This study demonstrates that carrier evacuation from a Coulomb potential effectively plays an important role in the electrical conduction of organic thin films. (C) 2012 Elsevier B.V. All rights reserved.

We have fabricated a field effect transistor structure using the charge-ordered (CO) organic material alpha-(BEDT-TTF)(2)I-3 to investigate the effects of electrostatic carrier injection. We have observed both n-type and bipolar behaviors in the CO state, whereas, previously, only n-type characteristics were reported. The present results indicate that the transfer characteristics for a negative gate voltage, i.e., hole transport characteristics, are highly dependent on the interface conditions between alpha-(BEDT-TTF)(2)I-3 and the electrodes and/or gate insulator. In addition, the activation energy of the CO state is essentially independent of V-SG. This result suggests the robustness of the CO state to electrostatic charge carrier injection.

The dicyano(phthalocyaninato)iron molecular conductor shows the Giant Magnetoresistance (GMR) effect. In order to investigate the effect of the molecular structure and charge on the X-ray absorption in the Fe(Pc)(CN)2 molecule, we measured the Fe K-edge X-ray Absorption Near Edge Structure (XANES) spectra in the TPP[Fe(Pc)L 2] 2 (L=CN, Br, and Cl), DMDP[Fe(Pc)(CN) 2], and [(n-C 2H 2) 4N][Fe(Pc)(CN) 2]. In 7134-7152 eV, we found the clear difference in the XANES spectra between these Fe(Pc)(CN) 2compounds. Our multiple scattering calculations indicate that the local structure of the iron and CN ligand, which tends to be changed by the nominal charge in the Pc ring, causes the spectral change.© 2012 The Surface Science Society of Japan.

Novel polymorph of the ferric spin crossover complex, beta-[Fe(qsal)(2)]I-3 [qsalH = N-(8-quinolyl) salicylaldimine], has been prepared and characterized by magnetic susceptibilities and Mossbauer spectra. beta polymorph exhibited a cooperative complete spin transition with a thermal hysteresis of 25 K and a tendency to be quenched in the high-spin (HS) state, which is contrastive to a gradual incomplete spin conversion in alpha polymorph.

Rare-earth-metal (M = Nd, Gd and Dy) complexes of the organic monoradicals, 15-crown-5-phenyl nitronyl nitroxide 1 and 15-crown-5- or 18-crown-6-phenyl iminonitroxide 2, were synthesized. We present here magnetic properties of the metal-free radicals and the metal complexes of these organic monoradicals studied using SQUID megnetometry. Almost of all the rare-earth-metal complexes show two-sublattice behavior in a wide range of antiferromagnetic (AFM) intrasublattice and ferromagnetic (FM) intersublattice interactions, Gamma and lambda, with vertical bar C Gamma vertical bar and vertical bar C lambda vertical bar. 10 to 100 K (C is the Curie constant) over the temperature range between 1.8 and 300 K, while the metal-free radicals exhibit only weak AFM intermolecular interactions, less than the Weiss constant theta = -1 K. The magnitude of interactions observed in the metal complexes of each radical increase in order from Gd to Dy to Nd complexes. [GRAPHICS] (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The synthesis, crystal and electronic structures, resistivity, magnetic susceptibility, and dielectric constant of the novel chiral crystal, alpha&apos;-(S,S-DMBEDT-TTF)(2)PF6 [DMBEDT-TTF = dimethylbis(ethylenedithio) tetrathiafulvalene] are presented. The alpha&apos;-type donor arrangement affords the one-dimensional antiferromagnetic behavior with J = -40 K. The calculated band structure indicates the pseudo-one-dimensional interaction in the molecular side-by-side direction along the b-axis. The frequency-dependent dielectric constant suggests the charge disproportionation above 100K. The non-centrosymmetric space group due to the composed chiral molecules affords the possibility of piezoelectricity. (C) 2011 Elsevier B.V. All rights reserved.

The field of molecular conductors was pioneered by works on the semiconducting properties of phthalocyanines and condensed aromatic hydrocarbons in the middle of the last century. Around three decades ago, the first organic superconductor was reported. Since then, various new molecular superconductors based on multichalcogen pi molecules such as bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), dimethyl(ethylenedithio)diselenadithiafulvalene (DMET), BETS (or BEDT-TSF=bis(ethylenedithio)tetraselenafulvalene), and [M(dmit)(2)] (M=Ni, Pd; dmit=4,5-dimercapto-1,3-dithiole-2-thione) including unprecedented antiferromagnetic and field-induced organic superconductors and the first single-component molecular metals were developed by the members in the Department of Chemistry of the University of Tokyo along with outside collaborators. Studies on the physical properties-especially optical properties-of various types of molecular conductors are also extensively examined.

Experiments on photoinduced charge carrier extraction using linearly increasing voltage (photo-CELIV) are reported for an organic thin-film device having an active layer of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) below 90K down to 1.6 K. CELIV peaks for different rates of voltage increase appear at almost the same electric fields at a temperature below 30 K. From this result, it is concluded that the CELIV signal does not reflect mobility at low temperatures. An analytical model that relates low-temperature CELIV signals to the trap density function is proposed.

The partially-oxidized TPP[M(Pc)L-2](2) molecular conductors exhibit variable electronic and magnetic transport bulk materials properties due to central metal and axial ligand molecular modifications. The controllable electrical conductivity and giant negative magnetoresistance can be mainly attributable to the varying ligand field energy and physical bulkiness of the axial ligands which cause modulation in the intra-molecular pi-d (Pc-M) and inter-molecular pi-pi (Pc-Pc) interactions in the TPP[M(Pc)L-2](2) system, respectively. Characterization of the electronic conduction band utilizing one-dimensional (1-D) tight-binding approximation from infrared reflectance and thermoelectric power profile reveal consistent band widths of 0.43 eV-0.62 eV for the Co series (L = Br &lt; Cl &lt; CN) and 0.44-0.56 eV for the Fe series (L = Br &lt; Cl &lt; CN). The fixed band width suggests that stable electron conduction bands (transport pathway) can be constructed which can withstand the molecular pi-d interaction modifications that severely alter the bulk electronic and magnetic materials properties of the TPP[M(Pc)L-2](2) molecular conductors.