小簑 剛

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.

A simple way to control only the surface properties of polymer materials, without changing the bulk properties, has long been desired. The segregation behavior when a component with a tiny amount fed into the matrix is thermodynamically enriched at the surface is one of the candidate methods. This capability was examined herein by focusing on a star-shaped polyhedral oligomeric silsesquioxane (s-POSS), where the central POSS unit is tethered to eight isobutyl-substituted POSS cages as a surface modifier. X-ray photoelectron spectroscopy revealed that the surface of a film of poly(methyl methacrylate) (PMMA) was almost completely covered with POSS units by adding just 5 wt % s-POSS to it. The segregated POSS dramatically altered the physical properties such as molecular motion and the mechanical and dielectric responses at the surface of the PMMA film. These findings make it clear that s-POSS is an excellent surface modifier for glassy polymers.

<p>Suitable intermolecular hydrogen bonding enables the formation of a fixed 3D supramolecular framework and suppresses the exciton nonradiative decays and quenching.</p>

© 2019 Elsevier B.V. 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 (CI) 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 CI 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 CI directly from the ACM data. Subsequently, it was possible to evaluate the injection barriers at the metal-free phthalocyanine (H2Pc)–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.

Near-infrared organic light-emitting diodes and semiconductor lasers could benefit a variety of applications including night-vision displays, sensors and information-secured displays. Organic dyes can generate electroluminescence efficiently at visible wavelengths, but organic light-emitting diodes are still underperforming in the near-infrared region. Here, we report thermally activated delayed fluorescent organic light-emitting diodes that operate at near-infrared wavelengths with a maximum external quantum efficiency of nearly 10% using a boron difluoride curcuminoid derivative. As well as an effective upconversion from triplet to singlet excited states due to the non-adiabatic coupling effect, this donor-acceptor-donor compound also exhibits efficient amplified spontaneous emission. By controlling the polarity of the active medium, the maximum emission wavelength of the electroluminescence spectrum can be tuned from 700 to 780 nm. This study represents an important advance in near-infrared organic light-emitting diodes and the design of alternative molecular architectures for photonic applications based on thermally activated delayed fluorescence.

The development of host materials with high performance is essential for fabrication of efficient and stable organic light-emitting diodes (OLEDs). Although host materials used in OLEDs are typically organics, in this study, it is shown that the organic-inorganic perovskite CH3NH3PbCl3 (MAPbCl(3)) can be used as a host layer for OLEDs. Vacuum-evaporated MAPbCl(3) films have a wide band gap of about 3 eV and very high and relatively balanced hole and electron mobilities, which are suitable for the host material. Photoluminescence and electroluminescence take place through energy transfer from MAPbCl(3) to an organic emitter in films. Incorporation of an MAPbCl(3) host layer into OLEDs leads to a reduction of driving voltage and enhancement of external quantum efficiency as compared to devices with a conventional organic host layer. Additionally, OLEDs with an MAPbCl(3) host layer demonstrate very good operational stability under continuous current operation. These results can be extensively applied to organic- and perovskite-based optoelectronics.

Horizontal orientation of the emission transition dipole of light-emitting molecules plays a critical role in the light outcoupling efficiency and the performance of organic light-emitting diodes. It is well established that linear and planar small molecules are generally preferred to achieve such a horizontal molecular orientation in vapor-deposited organic thin films. Here, we designed and synthesized four novel carbazole-based thermally-activated delayed fluorescence (TADF) molecules with different shapes and degrees of planarity in order to examine the influence of the emitter structure on the molecular orientation and the electroluminescence properties in TADF OLEDs. Molecular orientation of the TADF molecules in neat films and in blends was investigated using variable angle spectroscopic ellipsometry and angle dependent photoluminescence measurements, respectively. The results provide new important insights into the influence of the planarity of TADF molecules on their molecular orientation in vapor-deposited organic thin films. The photophysical and electroluminescence properties of these TADF molecules were then investigated to examine the influence of the molecular orientation on the performance of TADF OLEDs. The most efficient device was obtained using the TADF emitter showing a nearly perfect horizontal orientation of the emitting dipoles in the blend films. The maximum electroluminescence external quantum efficiency measured in this device was found to be 15.4%, which is about 1.75 times higher than the theoretical value calculated using an isotropic distribution of transition dipoles.

Improving the performance of blue organic light-emitting diodes (OLEDs) is needed for full-colour flat-panel displays and solid-state lighting sources. The use of thermally activated delayed fluorescence (TADF) is a promising approach to efficient blue electroluminescence. However, the difficulty of developing efficient blue TADF emitters lies in finding a molecular structure that simultaneously incorporates (i) a small energy difference between the lowest excited singlet state (S-1) and the lowest triplet state (T-1), Delta E-ST, (ii) a large oscillator strength, f, between S-1 and the ground state (S-0), and (iii) S-1 energy sufficiently high for blue emission. In this study, we develop TADF emitters named CCX-I and CCX-II satisfying the above requirements. They show blue photoluminescence and high tripletto- singlet up-conversion yield. In addition, their transition dipole moments are horizontally oriented, resulting in further increase of their electroluminescence efficiency. Using CCX-II as an emitting dopant, we achieve a blue OLED showing a high external quantum efficiency of 25.9%, which is one of the highest EQEs in blue OLEDs reported previously.

Thermally activated delayed fluorescence (TADF) [GRAPHIC] materials have shown great potential for highly efficient organic light-emitting diodes (OLEDs). While the current molecular design of TADF materials primarily focuses on combining donor and acceptor units, we present a novel system based on the use of excited-state intramolecular proton transfer (ESIPT) to achieve efficient TADF without relying on the well-established donor-acceptor scheme. In an appropriately designed acridone-based compound with intramolecular hydrogen bonding, ESIPT leads to separation of the highest occupied and lowest unoccupied molecular orbitals, resulting in TADF emission with a photoluminescence quantum yield of nearly 60%. High external electroluminescence quantum efficiencies of up to 14% in OLEDs using this emitter prove that efficient triplet harvesting is possible with ESIPT-based TADF materials. This work will expand and accelerate the development of a wide variety of TADF materials for high performance OLEDs.

The dipole orientation of guest emitters doped into host matrices is usually investigated by angular dependent photoluminescence (PL) measurements, which acquire an out-of-plane PL radiation pattern of the guest-host thin films. The PL radiation patterns generated by these methods are typically analysed by optical simulations, which require expertise to perform and interpret in the simulation. In this paper, we developed a method to calculate an orientational order parameter S without the use of full optical simulations. The PL radiation pattern showed a peak intensity (I-sp) in the emission direction tilted by 40 degrees-60 degrees from the normal of the thin film surface plane, indicating an inherent dipole orientation of the emitter. Thus, we directly correlated I-sp with S. The S - I-sp relation was found to depend on the film thickness (d) and refractive indices of the substrate (n(sub)) and the organic thin film (n(org)). Hence, S can be simply calculated with information of I-sp, d, n(sub), and n(org). We applied our method to thermally activated delayed fluorescence materials, which are known to be highly efficient electroluminescence emitters. We evaluated S and found that the error of this method, compared with an optical simulation, was less than 0.05.

By preparing parallelly aligned 1.9-mu m-high SiO2 microfluidic channels on an indium tin oxide substrate surface, the solution flow direction during spin-coating was controlled to be parallel to the grating. Using this technique, a pentafluorene-4,4'-bis(N-carbazoly1)-1,11-biphenyl (CBP) binary solution in chloroform was spin-coated to embed a 40-50 nm-thick 10 wt %-pentafluorene:CBP thin film in the channels. In-plane polarized photoluminescence measurements revealed that the pentafluorene molecules tended to orient along the grating, demonstrating that one-dimensional fluid flow can control the in-plane molecular orientation. Furthermore, the dependences of the photoluminescence anisotropy on the spin speed and substrate material suggest that the velocity of the solution flow and/or its gradient in the vertical direction greatly affects the resulting orientation. This indicates that the mechanism behind the molecular orientation is related to stress such as the shear force. The effect of the solution flow on the molecular orientation was demonstrated even in organic light-emitting diodes (OLEDs). Linearly polarized electroluminescence was obtained by applying the in-plane orientation to OLEDs, and it was found that the dichroic ratio of the electroluminescence orthogonal (x) and parallel (y) to the grating is x/y = 0.75.

The influences of film density and molecular orientation on the carrier conduction and air stability of vacuum-deposited amorphous organic films of N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (alpha-NPD) were investigated. The substrate temperature (T-sub) during vacuum deposition had different effects on the film density and molecular orientation of alpha-NPD. Film density was a concave function of T-sub; maximum density was attained at T-sub, = 270-300 K. alpha-NPD molecules were randomly oriented at T-sub, = 342 K, and their horizontal orientation on the substrate became dominant as T-sub:, decreased. Hole current and air stability were clearly raised by increasing the film density by 1 to 2%; these effects were, respectively, attributed to carrier hopping between neighboring alpha-NPD molecules and suppressed penetration of oxygen and water. These results imply that increasing film density is more effective to enhance the electrical performance of organic thin-film devices with alpha-NPD films than control of molecular orientation.

A complete horizontal molecular orientation of a linear-shaped thermally activated delayed fluorescent guest emitter 2,6-bis(4-(10Hphenoxazin-10-yl)phenyl)benzo[1,2-d:5,4-d'] bis(oxazole) (cis-BOX2) was obtained in a glassy host matrix by vapor deposition. The orientational order of cis-BOX2 depended on the combination of deposition temperature and the type of host matrix. Complete horizontal orientation was obtained when a thin film with cis-BOX2 doped in a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) host matrix was fabricated at 200 K. The ultimate orientation of guest molecules originates from not only the kinetic relaxation but also the kinetic stability of the deposited guest molecules on the film surface during film growth. Utilizing the ultimate orientation, a highly efficient organic light-emitting diode with the external quantum efficiency of 33.4+/-2.0% was realized. The thermal stability of the horizontal orientation of cis-BOX2 was governed by the glass transition temperature (T-g) of the CBP host matrix; the horizontal orientation was stable unless the film was annealed above T-g. Published by AIP Publishing.

Newly developed thermally activated delayed fluorescence (TADF) materials are attractive for application in efficient displays. Five TADF materials, including PXZ-TRZ and four carbazolyl dicyanobenzene (CDCB) derivatives of 4CzTPN, 4CzTPN - Ph, 2CzPN, and 4CzIPN, were investigated using terahertz spectroscopy in the 0.60-1.60 THz range. While PXZ-TRZ was almost transparent, the carbazolyl dicyanobenzene (CDCB) derivatives, especially 4CzIPN, exhibited intrinsic absorption features. Comparing these results with density functional theorem calculations, each absorption feature was clarified to originate from the intramolecular motions of the carbazole units. (C) 2016 Optical Society of America

Horizontal orientation of light-emitting chromophores plays a critical role in the light outcoupling efficiency and the overall performances of organic light-emitting diodes. Here, we demonstrate that such a horizontal orientation of light-emitting molecules can be achieved in solution-processed blends containing highly fluorescent oligofluorenes dispersed into various small molecule host materials. The influences of the host material, the solvent used for the spin-coating, the doping concentration of the oligofluorenes and the oligofluorene chemical structure on these orientational processes are investigated using variable angle spectroscopic ellipsometry and angle-dependent photoluminescence measurements. By clarifying the roles played by these parameters in the horizontal orientation of the emitters, the results provide crucial insights into these molecular orientational processes in spin-coated glassy organic thin films, which should be relevant for the development of high-efficiency solution-processed organic light-emitting diodes in the near future.

Horizontal orientation of the emission transition dipole moments achieved in glassy vapor-deposited organic thin films leads to an enhancement of the light out-coupling efficiency in organic light-emitting diodes (OLEDs). Here, our combined study of variable angle spectroscopic ellipsometry and angle dependent photoluminescence demonstrates that such a horizontal orientation can be achieved in glassy spin-coated organic films based on a composite blend of a heptafluorene derivative as a dopant and a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl as a host. Solution-processed fluorescent OLEDs with horizontally oriented heptafluorene emitters were then fabricated and emitted deep blue electroluminescence with an external quantum efficiency as high as 5.3%. (C) 2015 AIP Publishing LLC.

We report on optically pumped blue, green, and red liquid organic distributed feedback (DFB) lasers based on solvent-free fluidic organic semiconductors, and prepared on highly flexible corrugated polymeric patterns. By the appropriate selection of laser dyes doping a liquid 9-(2-ethylhexyl) carbazole host, the lasing wavelength is effectively tuned across the visible spectrum via a cascade energy transfer scheme. We also demonstrate a mechanical tunability of the flexible liquid DFB laser emission, which is due to the deformation of the high-aspect ratio DFB grating under bending. Overall, this work provides an important step in the development of flexible liquid organic optoelectronic devices. (C) 2015 AIP Publishing LLC.

The dependence of the morphology of neat chloroaluminum phthalocyanine (ClAlPc) films on substrate temperature (T-sub) during deposition is investigated by variable angle spectroscopic ellipsometry (VASE), x-ray diffraction (XRD), and atomic force microscopy (AFM) to obtain detailed information about the molecular orientation, phase separation, and crystallinity. AFM images indicate that both grain size and root mean square (RMS) roughness noticeably increase with T-sub both in neat and blend films. Increasing T-sub from room temperature to 420 K increases the horizontal orientation of the ClAlPc molecules with an increase of the mean molecular tilt angle from 60.13 degrees (300 K) to 65.86 degrees (420 K). The UV-vis absorption band of the corresponding films increases and the peak wavelength slightly red shifts with the T-sub increase. XRD patterns show a clear diffraction peak at T-sub over 390 K, implying the p-stacking of interconnected ClAlPc molecules at high T-sub. Planar and bulk heterojunction (BHJ) photovoltaic cells containing pristine ClAlPc films and ClAlPc: C-60 blend films fabricated at T-sub of 390 K show increases in the power conversion efficiency (eta(PCE)) of 28% (eta(PCE) = 3.12%) and 36% (eta(PCE) = 3.58%), respectively, relative to devices as-deposited at room temperature. The maximum short circuit current in BHJs is obtained at 390 K in the T-sub range from 300 K to 450 K.

Efficient organic light-emitting diodes have been developed using emitters containing rare metals, such as platinum and iridium complexes. However, there is an urgent need to develop emitters composed of more abundant materials. Here we show a thermally activated delayed fluorescence material for organic light-emitting diodes, which realizes both approximately 100% photoluminescence quantum yield and approximately 100% up-conversion of the triplet to singlet excited state. The material contains electron-donating diphenylamin-ocarbazole and electron-accepting triphenyltriazine moieties. The typical trade-off between effective emission and triplet-to-singlet up-conversion is overcome by fine-tuning the highest occupied molecular orbital and lowest unoccupied molecular orbital distributions. The nearly zero singlet-triplet energy gap, smaller than the thermal energy at room temperature, results in an organic light-emitting diode with external quantum efficiency of 29.6%. An external quantum efficiency of 41.5% is obtained when using an out-coupling sheet. The external quantum efficiency is 30.7% even at a high luminance of 3,000 cdm(-2).

Comparative studies of the effects of a series of polycrystalline donors on the performance of 95 wt.%-C-70-based bulk-heterojunction (BHJ) photovoltaics were conducted. A BHJ based on the wide band-gap molecule dinaphthothienothiophene (DNTT) shows power conversion efficiency (eta(PCE)) of up to 4.28%. The photovoltaic parameters are superior to those of devices using the similar molecule pentacene (PEN) or polycrystalline copper phthalocyanine (CuPc) for donor concentrations from 5 to 30 wt.%. The low-lying DNTT ionization potential and the high mu(h) in the DNTT blend support the excellent DNTT device performance. The low performance of BHJs with 5 wt.% PEN and 5 wt.% CuPc may stem from strong exciplex recombination in the PEN: C-70 blend and limited hole mobility combined with geminate polaron-pair recombination in the CuPc: C-70 blend. The zero-field hole mobility of the blends with 5 wt.% donor has a positive correlation with the corresponding device performance. The eta(PCE) of a 5 wt.%-DNTT BHJ cell was improved to 4.92% by optimizing the cathode buffer layer. (C) 2014 Elsevier B.V. All rights reserved.

The orientational order of a linear-shaped thermally activated delayed fluorescent dopant 10-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-10H-phenoxazine (PXZ-TRZ) was selectively controlled in a randomly oriented host matrix composed of 3,3-di(9H-carbazol-9-yl)biphenyl (mCBP) by varying the temperature during deposition of the thin films. Although the molecular orientation of mCBP was random at deposition temperatures ranging from 200 to 300 K (orientational disorder), PXZ-TRZ molecules oriented horizontal to the substrate in this temperature range (high orientational order). This indicates that the orientational order was dominated by the kinetic behavior of PXZ-TRZ at the film surface rather than by randomization caused by aggregation of PXZ-TRZ and mCBP molecules. Using an orientation-controlled 6 wt % PXZ-TRZ:mCBP film as an emitting layer, we fabricated organic light-emitting diodes (OLEDs). The horizontal orientation of the dopants enhanced the external electroluminescence quantum efficiency of the OLED by 24% compared with that of the corresponding OLED with slightly vertical orientation. An optical simulation found that the enhancement originates mainly from the improvement of the light out-coupling efficiency.

The thermal annealing treatment of an organic non-crystalline film of spirofluorene causes the randomization of the molecular orientation through molecular migration. However, the magnitude of the randomization depends on the depth in the film. The comparison of variable-angle spectroscopic ellipsometry, thermally stimulated current, and field-effect transistor characteristics measurements revealed that the molecular orientation in the bulk was randomized by annealing but was still partially maintained at the organic/substrate interface. This difference in condensed states between the interface and the bulk originates from a difference in glass transition temperature. (C) 2013 Elsevier B. V. All rights reserved.

Efficient bulk heterojunction (BHJ) photovoltaic cells (PVs) based on 5 wt.% donors and C-70 were fabricated. Tris[4-(5-phenylthiophen-2-yl)phenyl]-amine (TPTPA)-based BHJ PVs show higher power conversion efficiency (eta(PCE)) than aluminum phthalocyanine chloride-based BHJ PVs. Although the absorption of AlPcCl is complementary to that of C-70, TPTPA's high hole mobility and symmetrical molecular structure are likely to be crucial contributing factors to the higher eta(PCE). Phase separation occurs in the 5%-TPTPA blend. The device was optimized via replacement of the bathocuproine buffer by a combination of 3,4,9,10-perylenetetracarboxylic bis-benzimidazole and bathocuproine. eta(PCE) of 5.96% is achieved because of the decreased series resistance. (C) 2013 AIP Publishing LLC [http://dx.doi.org/10.1063/1.4801954]

Highly efficient photovoltaic cells based on a bulk heterojunction configuration composed of C70 with various donor materials at 5 wt.% donor concentration were fabricated. The tetraphenyldibenzoperiflanthene (DBP) donor achieved the highest power conversion efficiency (ηPCE) of 6.4% for the optimized cell. The improved performance with DBP arises from a combination of a higher absorption coefficient than 1,1-bis-(4-bis(4-methyl- phenyl)-amino-phenyl)-cyclohexane and a symmetrical molecular structure. The high ηPCE with only 5 wt. donor is attributed to a sufficient donor concentration for enhanced Frenkel exciton dissociation in C70, while efficiency and electron mobility decrease at higher donor concentrations. © 2013 AIP Publishing LLC.

Combining droplet manipulation by the application of an electric field with inkjet printing is proposed as a unique technique to control the surface wettability of substrates for solution-processed organic field-effect transistors (FETs). With the use of this technique, uniform thin films of 2,7-dioctyl[1]benzothieno[2,3,-b][1]benzothiopene (C-8-technique, uniform thin films of 2,7-dioctyl[1]benzothieno[2,3,-b][1]benzothiopene (C-8-BTBT) could be fabricated on the channels of FET substrates without self-assembled monolayer treatment. High-speed camera observation revealed that the crystals formed at the solid/liquid interface. The coverage of the crystals on the channels depended on the ac frequency of the external electric field applied during film formation, leading to a wide variation in the carrier transport of the films. The highest hole mobility of 0.03 cm(2) V-1 s(-1) was obtained when the coverage was maximized with an ac frequency of 1 kHz.

The efficiency roll-off characteristics in highly efficient thermally activated delayed fluorescence (TADF) based organic light-emitting diodes (OLEDs) were effectively suppressed by controlling the molecular orientation of a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) host matrix. The hole mobility in the light 2 emitting layer was found to govern the magnitude of this suppression. Three-dimensional finite-difference time-domain calculations and photoluminescence quantum yield measurements revealed that the optical characteristics of the fabricated devices and photophysical properties of the TADF emitter did not affect efficiency roll-off CBP molecules adopted random orientations when films were fabricated at high temperature (350 K), resulting in low hole mobility, and shifting the recombination zone away from the interface of the emitting layer with the electron transporting layer. When CBP was randomly orientated, efficiency roll-off was suppressed by 30% at a current density of 100 mA cm(-2). This result indicates that control of the molecular orientation of the host can allow us to indirectly tune the carrier balance in OLEDs.

The molecular orientational randomization dynamics of organic thin films during annealing were measured by real-time in situ ellipsometry. The spirofluorene derivatives used in this work formed amorphous thin films with the molecules oriented parallel to the substrates when the films were vacuum deposited at room temperature. However, the molecular orientations became random when the thin films were annealed at temperatures higher than the glass transition temperature because molecular migration occurred. Analysis of the ellipsometry results using a graded model showed that the randomization of the molecular orientations depended on the thickness of the thin film. This suggests that the surface glass transition temperatures are lower than the bulk glass transition temperatures in the thin films of these small molecules.

The temperature dependence of luminescence from [Cu(dnbp)(DPEPhos)]BF4 (dnbp = 2,9-di-n-butylphenanthroline, DPEPhos = bis[2-(diphenylphosphino)phenyl]ether) in a poly(methyl methacrylate) (PMMA) film indicates the presence of long-life green emission arising from two thermally equilibrated charge transfer (CT) excited states and one non-equilibrated triplet ligand center (3LC) excited state. At room temperature, the lower triplet CT state is found to be the predominantly populated excited state, and the zero-zero energy of this state is found to be 2.72 eV from the onset of its emission at 80 K. The tunable emission maximum of [Cu(dnbp)(DPEPhos)]BF4 in various hosts with different triplet energies is explained in terms of the multiple triplet energy levels of this complex in amorphous films. Using the high triplet energy charge transport material as a host and an exciton-blocking layer (EBL), a [Cu(dnbp)(DPEPhos)]BF4 based organic light-emitting diode (OLED) achieves a high external quantum efficiency (EQE) of 15.0%, which is comparable to values for similar devices based on Ir(ppy)3 and FIrpic. The photoluminescence (PL) and electroluminescence (EL) performance of green emissive [Cu(mu I)dppb]2 (dppb = 1,2-bis[diphenylphosphino]benzene) in organic semiconductor films confirmed its 3CT state with a zero-zero energy of 2.76 eV as the predominant population excited state.

The dependence of the amplified spontaneous emission threshold (E-th) on molecular orientation in vacuum deposited thin films fabricated from diphenyldiamine- and carbazole-substituted spirofluorene derivatives was investigated. The molecular orientations were modified by changing the substrate temperature during deposition and were almost parallel to the substrate at around 300 K in all of the films. The orientation became random in the film containing diphenyldiamine compound at around 380 K, resulting in decreased optical anisotropy. However, for the carbazole compound, the molecular orientation scarcely changed from 300 to 380 K, while the root-mean-square roughness increased from 0.28 to 0.94 nm. E-th approximately doubled for both the films when the optical anisotropy decreased because of the randomization of molecular orientation or when the surface roughness increased.

We have successfully obtained spin-coated films of unsubstituted planar phthalocyanines (free-base and copper phthalocyanine) from trifluoroacetic acid and chlorobenzene mixed solutions for the first time. The pre-annealed films did not consist of pure phthalocyanines; these films contained the solvent molecules. However, the residual solvent molecules could be removed by annealing at 425 K for 2 h in vacuum. This technique is useful for fabricating unsubstituted planar phthalocyanine thin films. (C) 2009 Elsevier B.V. All rights reserved.

To investigate the relationship between molecular orientation and current voltage (J-V) characteristics, molecular orientation and J-V characteristics have been simultaneously measured in some indium tin oxide (ITO)/X/Al structures. X were thin films fabricated from poly(3-hexylthiophene) (P3HT), coumarin6 dispersed in poly(N-vinylcarvazole), or biomolecular hemin (Hm). The results have shown that the orientation change of the P3HT chain causes a reproducible loop of the J-V characteristics in P3HT thin film, and that the peak observed in the J-V characteristics in Hm is associated with irreversible molecular orientation change. © 2008 Elsevier B.V. All rights reserved.

Simultaneous measurement of molecular orientation and current as a function of voltage has been conducted. Molecular orientation was measured using the polarization dependence of intramolecular electronic transition. In ITO/poly(3-hexylthiophene)/Al structure, it was found that the molecular orientation change assists the hysteretic current-voltage (J-V) characteristics. The result indicates that this measuring method can be useful in investigating the effects of molecular orientation change on unusual J-V characteristics. Copyright © 2008 The Chemical Society of Japan.

We fabricated ITO/biomolecule/Al junctions using chrolophyll a, cytochrome c, myoglobin, hemin, Vitamin B-12. All the junctions worked as organic light-emitting diode (OLED). The quantum efficiencies of the fabricated OLED were of the order of 1 x 10(-7) around V = 10 V, and did not seriously depend on whether or not a compound exhibits photoluminescence. Based on the energy diagram of the ITO/cytochrome c/Al junction, we discuss the difference of the EL spectrum from the photoluminescence or absorption spectrum. (c) 2005 Elsevier B.V. All rights reserved.

We fabricated biomolecular light-emitting diodes (BIODE) using hemin, and measured the electroluminescence (EL) spectra, current-voltage and EL intensity-voltage characteristics. The current-voltage and EL intensity-voltage characteristics revealed an irreversible transition of hemin for the applied voltage of V approximate to 4.5 V. above which drastic changes of the EL spectra occur. In order to clarify the origin of this voltage-induced transition, we determined the spin state of several compounds containing heme (hemin, myoglobin, and cytochrorne c) using magnetic susceptibility and Raman spectra. We clarified the features of the EL spectra of heme compounds both in the oxidized low-spin state and in the oxidized high-spin state. Based on the spectral features thus obtained, we concluded that the voltage-induced transition in hemin is associated with the change of iron from the oxidized high-spin state (S = 5/2) to the oxidized low-spin state (S = 1/2).

We fabricated organic-light-emitting diode (OLED) from chlorophyll a, and measured electroluminescence (EL) and photoluminescence (PL) spectra. The EL spectrum exhibits a peak at 700 nm and a shoulder at 750 nm, while the PL spectrum exhibits a peak at 750 nm. The external quantum efficiency of the fabricated OLED linearly increases for the applied voltage above V = 4 V and reaches to 9 x 10(-8) at V = 8 V.