中村 一希

© Copyright Materials Research Society 2018. Ag deposition-based multicolor electrochromic (EC) device we reported can switch various optical states among transparent, black, silver, cyan, magenta, and yellow by only using electrochemical deposition of Ag. However, the EC device had poor color retention property under open-circuit state because of dissolution of deposited Ag metal by Cu2+ ions, which is essential because it acts as redox material at counter electrode. Here, we introduced an anion exchange membrane to separate Cu2+ from the Ag deposit. The improved device achieved longer retention time of colored state. It is effective to maintain the coloring state without electric power for practical application.

© 2017 Elsevier B.V. Electrochromic-based optical modulation devices have attracted much interest because of potential application for electric papers and smart windows. We have reported Ag deposition-based optical modulation device which showed reversible changes of optical states between clear transparent and silver-mirror. In the device, formation of silver halide complexes greatly affected the optical states of silver electrodeposit. In this research, the effects of silver halide complexes were investigated by changing halide anion species in terms of the optical properties of the EC devices. The stability of the silver halide complex induced change in reduction voltage to form silver nanoparticles. Diffusion coefficients and electrode reaction rates also have effects on morphology of deposited Ag nanoparticles and resulting optical properties.

© 2018 The Royal Society of Chemistry. DNA-based functional materials are of great interest in electrical and optical device applications. In this paper, novel DNA-based photo-functional materials were fabricated by associating a DNA-lipid complex with a luminescent Eu(iii) complex. Interactions between DNA-lipid and Eu(iii) complexes were investigated by photophysical measurements in both solution and film states. The emission properties of the Eu(iii) complex were improved by association with the DNA-lipid complex in the film state. The emission intensity, quantum yield, and thermal stability of the Eu(iii) complex hosted by the DNA-lipid matrix were superior to those of the complex in a conventional poly(methyl methacrylate) matrix. Furthermore, the Eu(iii) complex in the DNA-lipid film showed circularly polarized luminescence through excitation of the ligand moiety. The chiral environment of the DNA matrix provides optical chirality to the interacting Eu(iii) complex.

© the Owner Societies 2018. Despite the application of electrochromic (EC) technologies in various optical modulating devices, the challenge to achieve multicolour EC behavior in a single device still remains. However, because almost all EC materials exhibit a single colour change, only a few organic materials are able to undergo multiple colour switching within a single device. The development of multicolour EC applications is therefore highly limited. In this research, we fabricated an EC device (ECD) with the simple hybrid capacitor architecture, i.e. with a flat ITO electrode as the working side and an ITO particle-modified electrode as the counter side. We also employed an electrolyte containing both anodic and cathodic EC materials consisting of small organic molecules. In this novel ECD, each EC material successfully undergoes individual colour switching from light yellow to light green and magenta. The mechanism of a multicolour system represents a significant breakthrough towards a full-colour ECD, thereby expanding the potential of EC technology.

© 2018SPST. An electroswitching device that enables modulation of both photoluminescence and coloration was obtained. The device consisted of luminescent lanthanide(III) complex Eu(hfa)3(TPPO)2 (photoluminescence material) and an diheptyl viologen HV2+ (electrochromic material). Coloration and emission control were achieved by only electrochemical reactions of HV2+. The coloration of the device was controlled by HV2+ electrochromism. Photoluminescence control was also achieved by the HV2+ electrochromism via intermolecular energy transfer from the excited states of Eu(III) ions to colored HV+∙. However, there were some problems that the response time of switching between emission and coloration was quite slow (approximately 15 minutes), and the representation stability of switching between emission and coloration was low. These problems would be caused by absence of counter electrode reaction material against HV2+ redox. In order to improve the response time of the cell and decrease the driving voltage for dual-mode representation, we introduced prussian blue (PB) modified electrode as an electrochromical counter redox material.

© 2017 The Author(s). Electrochemiluminescence (ECL) refers to light emission induced by an electrochemical redox reaction. The stability, emission response, and light intensity of the ECL device are known to be improved by using an alternating current (AC) voltage. In this paper, an AC-driven ECL device is fabricated with DNA/Ru(bpy)32+ hybrid film-modified electrode. The Ru(bpy)32+ complex exhibits significant electrochemical reactivity in the DNA/Ru(bpy)32+ hybrid film prepared by electrochemical adsorption. The hybrid film contains unique micrometre-scale aggregates of Ru(bpy)32+ in DNA matrix. The physicochemical properties of the hybrid film and its AC-driven ECL characteristics in the electrochemical device are studied. Orange-coloured ECL is observed to be emitted from only the aggregated structures in the hybrid film at the high AC frequency of 10 kHz, which corresponds to a response time shorter than 100 μs.

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electrochemiluminescence (ECL) is a phenomenon in which light is emitted from excited species generated by electrochemical reactions at electrodes. Alternating-current-driven ECL (AC-ECL) devices show good brightness and fast ECL response in comparison to direct-current-driven ECL devices. In this report, we focus on the ECL intensity and long-term stability of blue-light-emitting AC-ECL systems. We used a mixed solvent of propylene carbonate and toluene (volume ratio=1 : 1) to achieve stable blue ECL from 9,10-diphenylanthracene (DPA) molecules. We analyzed the electrochemical, optical, and AC-ECL properties of DPA in this mixed solvent to investigate the effect of the stabilities of redox species on AC-ECL properties. We found that the composition of the electrolyte solution affects the stability of these species. We conclude that stability of generated active species is required to achieve good performance in blue AC-ECL devices.

© 2017 Elsevier B.V. The in situ electrode potentials of anodes and cathodes in electrochromic (EC) devices were investigated. The solution-based 2-electrode EC device was fabricated with electrolyte solutions containing anodic and cathodic EC molecules. The electrochemical reaction in a 2-electrode EC device was controlled by the electrode reaction when electroactive molecules in smaller concentrations were used. In addition, the electrode showing less electrochemical activity in the EC device was subjected to larger overpotential under the application of a driving voltage, leading to the promotion of the redox reaction at the electrode. The results showed that the electrode potentials of the device were spontaneously regulated to facilitate both electrode reactions. It is very important to know the potential at each electrode in order to understand the reaction in detail in the 2-electrode EC device.

© 2017, Tokai University. All rights reserved. Recently, DNA-CTMA lipid complex as the environmentally-friendly materials has been investigated extensively in novel functional optical and electronic devices. We have previously reported that the hysteresis mechanism of the nonvolatile transistor memory device in lower temperature region from -150 ~ -20oC (L. Liang et al. Organic Electronics 28, 2016, 294-298). In this study, the hysteresis mechanism in the high temperature region range from 25 ~ 150oC has been investigated through studying the temperature dependence of transfer characteristics, X-ray diffraction patterns (XRD), differential scanning calorimetry (DSC) as well as the dielectric performance of DNA-CTMA complex. The result indicates that the dipoles inside the DNA-CTMA stacking crystalline structure contribute to the appearance of hysteresis in bio-OTFT device at the high temperature.

© 2017 the Owner Societies. The electroresponsive switching of red photoluminescence based on the electrochemical coloration of cyan-magenta-green (CMG) viologen components was achieved by combining a luminescent Eu3+ chelate and viologen derivatives, resulting in CMG coloration in a single cell. The cell coloration was controlled by an electrochromic (EC) reaction, which also modulated the photoluminescence of the Eu3+ chelate with high contrast, by transferring energy from the excited state of the Eu3+ ion to the colored states of EC molecules. Cyclic voltammograms, photoluminescence spectra, absorption spectra, luminescence quantum yields, and luminescence lifetimes were measured to clarify the differences between the luminescence quenching and energy transfer efficiencies for each C, M, and G coloration associated with the electrochromism. Thus, the spectral overlap between the luminescence band of the Eu3+ chelate and the absorption band of the colored EC molecules was proven to affect the efficiency of luminescence modulation.

© Copyright 2016 Society for Information Display Electrochromism, phenomenon of reversible color change induced by electrochemical redox reactions, is one of the prime candidates for full-color electronic paper. Recently, we reported Ag-deposition based multicolor electrochromic device showing color change between three primary colors of cyan, magenta, and yellow. These observed spectra include both absorbing and reflectance components. Therefore, it is necessary to separate these components in order to analyze coloration mechanism of the device. In this paper, coloration mechanisms of Ag deposition-based multicolor electrochromic device were investigated in terms of measurement of the actual absorption and actual reflection of the device. Morphologies of the deposited Ag nanoparticles were also investigated by FE-SEM, and then relationship between optical properties and deposited Ag morphologies was examined. As the results, color appearances of magenta and yellow state of the device were mainly dominated by absorption component of localized surface plasmon resonance of the deposited Ag nanoparticles. On the other hand, cyan state of the device was based on absorption as well as reflection component induced by thin film structure of the Ag deposit.

© 2016 The Japan Society of Applied Physics. We demonstrate a novel electrochemical dual-mode displaying (DMD) device, which enables control of both coloration and light emission using an electrochemical reaction. The coloration control of the DMD device was based on an electrochromic (EC) reaction, whereas the light emission of the device was caused by an electrochemiluminescence (ECL) mechanism. This novel DMD device consisted of a pair of facing conductive polymer-modified electrodes: comb-shaped interdigitated Au electrodes modified with poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) layers and poly(2,3-dihydrothieno-1,4-dioxin)-poly(styrene sulfonate) (PEDOT/PSS) film-modified indium tin oxide (ITO) electrodes. When a bias voltage was applied between the PEDOT/PSS film-modified ITO electrode and the comb-shaped electrodes, a color change of the device was observed by the EC reaction of the MEH-PPV and PEDOT/PSS. On the other hand, an emission was obtained when the bias voltage was applied between two comb-shaped interdigitated electrodes. The orange emission was ascribed to the ECL reaction of the MEH-PPV layer, which resulted from the formation of a p-i-n junction in this layer.

© 2015 Elsevier B.V. All rights reserved. An electroswitching device that enables modulation of both emission and coloration was obtained by combining luminesncent/electrochromic (EC) molecules of a fluoran molecule (Yellow-1) and 1,4-benzoquinone (BQ). Electroswitching of emission and coloration was achieved by the reversible electrochemically induced closing and opening of the lactone ring in Yellow-1. Neutral Yellow-1 was colorless and did not exhibit any fluorescence, while oxidized Yellow-1 (lactone ring-opened form) was yellow and displayed green fluorescence because of its extended, planar, and conjugated system. In order to achieve quick response time and high reversibility of the electroswitching optical device for modulating both emission and coloration, a BQ molecule was introduced as a bifunctional material. The inclusion of a redox-active moiety on the auxiliary electrode maintained the charge balance and acted as an EC molecule (transparent/yellow in neutral/reduced state, respectively). BQ acted as a bifunctional molecule, leading to quick and stable switching of both emission and coloration.

© 2015 Elsevier B.V. All rights reserved. Inorganic electrochromic (EC) materials are of interest because of their many possible applications, including use in information displays. The multifunctional EC materials that enable control of multiple colors and color depth have considerable promise as candidates for full color EC display devices. In this research, we focused on Ag nanoparticles that exhibit various colors on the basis of their localized surface plasmon resonance (LSPR). Because the LSPR band depends on the size and shape of the nanoparticles, control of the morphology of Ag nanoparticles can lead to dramatic changes in color. In order to apply this color variation for display devices, we utilized here the electrochemical formation of size-controlled Ag nanoparticles using a voltage-step method that consists of an application of two successive different voltages. In order to improve the variation of colors of the EC cell, the effect of application voltages and their times on morphology of deposited silver were investigated. The relationship between the morphology of the deposited Ag nanoparticles and color of the EC cell was discussed, and then we successfully represented multiple coloration of the EC cell with various color depth.

A dual-mode display device which can operate in both emissive and reflective modes, having advantages of both modes, is considerable promise as a next generation display. In this review, electrochemical switching systems, which enable simultaneous control of both emission and coloration, are reviewed in order to create the novel displaying materials. A luminescent europium(III) [Eu(III)] complexes, one of the important lanthanide (III) complexes, and electrochromic molecules of viologen derivatives were combined for appearance of the multi-functionality. The Eu(III) complex emission was controlled by the electrochromism of the viologen derivatives via an intermolecular energy transfer mechanism. When viologen derivatives were in a colorless state, a strong red emission was observed from the Eu(III) complex. On the other hand, the electrochemically colored viologen derivatives effectively quenched the red emission of the Eu(III) complex. However, these systems lacked quick response and high reversibility of the fluorescence modulations. Some of the researches for improving these disadvantage of primary study are described. Furthermore, numerical representations and multi-color representations with emissive and reflective modes were also achieved.

Leuco dyes, well-known multi-functional material, can exhibit excellent thermochromic properties by combining with developer molecule which is organic compound having a hydroxyl group and long alkyl chain. Our purpose of this research is to fabricate multifunctional material enabling control of both emission and coloration by combining leuco dye-developer system with emission materials. In this study, we investigated novel thermo-responsive dual-mode displaying media showing both reflective and emissive modes in red-green-blue (RGB) three primary colors. We employed the two kinds of leuco dye derivatives into the polymeric film as thermochromic material in order to improve the switching contrast of the emissive mode. As a result, we successfully demonstrated the control of coloration and emission in RGB colors with large contrast by thermal treatments.

Multifunctional materials such as those with thermo-switchable absorption or emission are widely applied to thermal recording media. We combined red-green-blue (RGB) thermochromic materials and luminescent materials in order to construct novel dual-mode display media that can control both coloration and emission. The composite films showed thermo-responsive control of RGB coloration with high reversibility through structural changes of nanoscale aggregates of the leuco dye and its developer. Moreover, RGB photoluminescence was also controlled by specific thermal treatment via intermolecular energy transfer from luminescent materials in the excited state to the colored leuco dyes.

銀析出型マルチカラーエレクトロクロミック素子について、積分球を用いた光学系により実吸収・実反射を測定し、析出銀の粒子形状との相関を検討、素子の発色機構の解析を行なった。マゼンタおよびイエローにおいては、微小な銀粒子による局在表面プラズモン共鳴の吸収が主に発色に寄与していた。一方で、シアン状態では、析出銀の粒径の増加および薄膜化により、吸収成分に加え長波長側の反射成分が増加することが、シアン状態の発現に寄与していることを明らかとした。

© 2015 Elsevier B.V. All rights reserved. A nonvolatile memory based on an organic thin-film transistor (OTFT) with a biopolymer of DNA-cetyltrimethylammonium chloride (DNA-CTMA) acting as the gate dielectric layer was fabricated. The transfer characteristics of the device prepared by both DNA alone and DNA-CTMA showed a very large and stable hysteresis. In order to analyze the memory mechanism, the temperature dependence of the transfer characteristics, electric conductivity, differential scanning calorimetry (DSC), thermally stimulated depolarization current (TSDC) as well as the dielectric property of the DNA-CTMA film have been investigated. As a result, the quasi-ferroelectric polarization originating from the alignment of the intrinsic dipole moment inside the DNA-CTMA complex was identified as the main source of hysteresis in the lower temperature region.

© 2016 the Owner Societies. Electrochemiluminescence (ECL) is a phenomenon in which light is emitted from the excited state of a redox-active material generated by electrochemical reactions. Among light-emitting devices, ECL devices have various advantages in terms of structure and ease of fabrication, and therefore, they are expected to be next-generation emitting devices. In this study, we introduced rutile-type titanium dioxide nanoparticles (TiO2 NPs) in a Ru(ii)-complex-based electrolyte to improve the emission properties of an alternating current (AC)-driven ECL device. The properties of the ECL device with TiO2 NPs were greatly improved (emission luminescence, 165 cd m-2; half-life time, 1000 s) compared to a previously reported AC-driven ECL device without nanoparticles. To determine how TiO2 NPs helped in achieving high emission luminescence and long-term stability, we measured the optical and electrochemical properties of the Ru(bpy)32+-based ECL solution in detail. The PL intensity of Ru(bpy)32+ was increased by adding TiO2 NPs, which indicated that the suppression of non-radiative quenching of the complex's excited states could improve the ECL intensity. With respect to the enhanced stability, electron transfers between Ru(bpy)32+ and TiO2 were suggested by detailed electrochemical measurements. These electron transfers occurred from the reduced Ru(bpy)32+ species to the TiO2, and subsequently, from the TiO2 to the oxidized Ru(bpy)32+ species. Such electron transfers are thought to improve the balance of the redox reactions in the ECL device, leading to long-term stability.

© The Royal Society of Chemistry 2016. Multifunctional materials such as those with thermo-switchable absorption or emission are widely applied to thermal recording media. We combined red-green-blue (RGB) thermochromic materials and luminescent materials in order to construct novel dual-mode display media that can control both coloration and emission. The composite films showed thermo-responsive control of RGB coloration with high reversibility through structural changes of nanoscale aggregates of the leuco dye and its developer. Moreover, RGB photoluminescence was also controlled by specific thermal treatment via intermolecular energy transfer from luminescent materials in the excited state to the colored leuco dyes.

© 2016 The Chemical Society of Japan. A novel electroresponsive multifunctional display device enabling control of both emission and transmittance was successfully fabricated. The device consisted of a liquid crystal-based electrolyte solution containing an electrochemically active luminescent material. Yellow electrochemiluminescence was observed from the device under application of alternating current voltage; modulation of its transmittance was also achieved when direct current voltage was applied to the device.

© The Royal Society of Chemistry. Electrochemical modulation of red luminescence from a europium(iii) complex has been demonstrated. In order to elucidate the mechanism of luminescence modulation, its cyclic voltammogram, absorption spectra, emission spectra, emission lifetime, and emission quantum yield were measured. From these measurements, the modulation of emission was found to be achieved through an electrochemical reaction of TiO2, which is facilitated by electron transfer between the europium(iii) complex and TiO2. Subsequent immobilization of the europium(iii) complex on a TiO2 electrode resulted in an on-off emission contrast of 74:1, with the response time and repetition stability of the emission switching being considerably improved.

Electrochemical modulation of red luminescence from a europium(III) complex has been demonstrated. In order to elucidate the mechanism of luminescence modulation, its cyclic voltammogram, absorption spectra, emission spectra, emission lifetime, and emission quantum yield were measured. From these measurements, the modulation of emission was found to be achieved through an electrochemical reaction of TiO2, which is facilitated by electron transfer between the europium(III) complex and TiO2. Subsequent immobilization of the europium(III) complex on a TiO2 electrode resulted in an on-off emission contrast of 74 : 1, with the response time and repetition stability of the emission switching being considerably improved.

© 2015 Old City Publishing, Inc. DNA/functional molecules complex have attracted a lot of attention for fabricating the DNA-based functional nanowire. In this paper, we fabricated DNA-based functional nanowire stretched and immobilized between a pair of electrodes. As the photo-electro functional material, tris(bipyridine) ruthenium(II) complex (Ru(bpy)<inf>3</inf>²⁺) was employed for fabricating the DNA-based functional molecular wire. The molecular structure and the photo-electro characteristics of the DNA/functional molecules were investigated. The Ru(bpy)<inf>3</inf>²⁺ was associated with duplex of DNA by not only electrostatic interaction but also intercalation in the aqueous solution. The molecular structure of DNA/Ru(bpy)<inf>3</inf>²⁺ complex on substrate was analyzed with AFM. As result we have found the network structures of DNA/Ru(bpy)<inf>3</inf>²⁺ complex on the mica substrate without any stretching treatments, which is similar to native DNA. The height of DNA/Ru(bpy)<inf>3</inf>²⁺ complex on the mica substrate was ranging from 0.8 to 1.6 nm, which was higher than the naked DNA (0.5-1.0 nm). This indicates that single-molecular DNA/Ru(bpy)<inf>3</inf>²⁺ complex also connects to each other to form network structures on a mica substrate. Then, in order to stretch the DNA complex between a pair of electrodes, high frequency and high electric field stretching methods were carried out. The structures of stretched and immobilized DNA-based functional nanowires were also analyzed with AFM. The I-V characteristics of DNA single molecule between electrodes were improved by the association of Ru(bpy)<inf>3</inf>²⁺.

© 2014 American Chemical Society. Inorganic electrochromic (EC) materials have various advantages for use in display devices. We demonstrate here a new multicolor EC device based on an electrochemical silver deposition mechanism. Ag nanoparticles electrochemically deposited on an electrode exhibit a wide variety of optical states based on their localized surface plasmon resonance (LSPR). As LSPR bands and the resultant colors change depending on the size and shape of the nanoparticles, morphological control of the Ag nanoparticles enables multiple color representation. In order to exploit this color variation in inorganic EC devices, we investigated the electrochemical deposition of size- and shape-controlled Ag nanoparticles by varying the surface morphology of the electrode and by applying a step voltage, which consisted of the application of two consecutive different voltages. Using only silver deposition, we have successfully achieved the first LSPR-based multicolor EC device that enables reversible color changes, including three primary colors-cyan, magenta, and yellow-as well as transparent, black, and mirror in a single cell.

© 2014SPST. Memory characteristics of organic field-effect transistors (OFETs) fabricated using poly(γ-methyl-L-glutamate) (PMLG) and poly(ε-benzyloxycarbonyl-L-lysine) [PLys(z)] as gate dielectrics are investigated. The origin of difference in the memory retention property in the transfer characteristics of the OFETs is investigated by thermally stimulated depolarized current (TSDC) and dielectric spectra measurements for the PLys(z) and PMLG films. TSDC measurements reveal that the depolarization of the PLys(z) film is mainly dominated by a single relaxation process around room temperature, but that of the PMLG film is not dominated by a relaxation process. Further, the PLys(z) film shows dielectric dispersion near room temperature, but the PMLG film does not show any dispersion. This causes difference in the electric characteristics of OFETs.

Multifunctional electroswitching of both emission and coloration was demonstrated by using fluoran derivatives in an electrolytic solution. Further, in order to investigate changes in the photophysical properties induced by electrical stimuli, we measured cyclic voltammogram, absorption spetra, emission spectra, and molecular orbital calculation. The mechanism for this electroswitching was attributed to the reversible electrochemically induced closing and opening of the lactone ring in the fluoran molecule. All neutral fluoran molecules were colorless and did not exhibit any fluorescence, while the oxidized (lactone ring-opened form) molecule was yellow and displayed a green fluorescence as a consequence of the extended, planar, conjugated system. Furthermore, this fluoran molecule achieved reversible electroswitchable emission and coloration with high on/off contrast. © 2014 American Chemical Society.

We fabricated a new bio-organic thin film transistor through applying DNA-octadecyltrimethylammonium chloride, (OTMA) as the gate dielectric. The optical analysis of the DNA complex film including UV spectra and CD measurement has been carried out to investigate the structure variation after the formation of complex via ion exchange reaction. In terms of electronic characteristics, compared with the device prepared by DNA alone, the ON/OFF current ratio of DNA-OTMA based device has been improved significantly. In addition, the fabricated device not only exhibited better hysteresis behavior through recording the transfer characteristic but also the stable memory performance based on the measurement of switching response. © 2014 by American Scientific Publishers.

We demonstrated organic field-effect transistors (OFETs) using nylon 11, poly(γ-methyl-L-glutamate) (PMLG), and poly(ε-benzyloxycarbonyl-L- lysine) [Plys(z)] as gate dielectrics. By a Fourier-transform IR (FT-IR) measurement, the secondary structure of nylon 11 was determined to be a β-sheet, and those of PMLG and Plys(z) have an a-helix. The orientation of the a-helix of PMLG and Plys(z) and its crystallinity were determined by FT-IR and X-ray diffraction (XRD) measurements, respectively. The OFET using nylon 11 showed no hysteresis in the transfer characteristic (on/off ratio is 1.2). In contrast, OFETs using PMLG and PLys(z) showed hysteresis and it operated as ferroelectric memories (on/off ratios are 2.2 x 104 and 53, respectively). This difference is attributed to the difference in the secondary structure and the crystal system. The memory retention property in OFETs using PMLG and PLys(z) suggested that high crystallinity of the film and highly ordered dipoles are not necessary for the memory retention. © 2014 The Japan Society of Applied Physics.

A thin-film transistor (TFT) non-volatile memory (NVM) device was fabricated using α-helix poly(γ-methyl-l-glutamate) (PMLG) as a ferroelectric layer. In order to study the mechanism of memory driving, the temperature dependence of transfer characteristics and memory performance was investigated. It was revealed that the cooperative movement of the large dipole moment along the rod-like main chain and that of the small dipole moment in the side chain played an important role in the memory function. © 2014 The Royal Society of Chemistry.

A thin-film transistor (TFT) non-volatile memory (NVM) device was fabricated using a-helix poly(gamma-methyl-L-glutamate) (PMLG) as a ferroelectric layer. In order to study the mechanism of memory driving, the temperature dependence of transfer characteristics and memory performance was investigated. It was revealed that the cooperative movement of the large dipole moment along the rod-like main chain and that of the small dipole moment in the side chain played an important role in the memory function.

エレクトロクロミズムとは，電気化学的な酸化還元反応により物質が可逆な色調変化を起こす現象であり，表示デバイスや調光デバイスへ利用されている．本研究では，電極上への銀の電気化学的な還元析出に基づく色調変化を示すエレクトロクロミック素子に関し，電極の表面形状が素子の光学特性に与える影響について評価した．平滑な電極表面を有するITO電極上へ銀を析出させた場合は，入射光を反射する良好な鏡状態を発現した．一方，平滑ITO電極一面をITO粒子によって被覆した電極上に銀を析出させた際には，ITO粒子膜の膜厚に依らず入射光を吸収する黒状態を発現することを明らかとした．さらに，これらの電極上への電着銀の析出形態の差異を評価し，光学特性の発現機構について解析した．

Multifunctional electrochromic materials that enable control of multiple colors, color density, and specular reflection are potential candidates for novel reflective display devices. In this research, we focus on Ag nanoparticles that exhibit various optical states based on their localized surface plasmon resonance (LSPR). Because the LSPR band depends on the size and shape of the nanoparticles, control of the morphology of Ag nanoparticles can lead to dramatic changes in color. In order to apply this color variation for display devices, we investigate here the electrochemical formation of size-controlled Ag nanoparticles using a voltage-step method that consists of an application of two successive different voltages (V1 and V2). The electrochemically deposited Ag nanoparticles appear red and blue depending on the time for V2 voltage application. The color changes between the transparent and colored states are reversible. Then, we successfully demonstrate the first LSPR-based multicolor electrochromic device in which reversible control of five optical states - transparent, silver mirror, red, blue, and black - is possible. © Copyright 2013 Society for Information Display.

The first localized surface plasmon resonance (LSPR)-based multicolor electrochromic device with five reversible optical states is demonstrated. In this device, the size of deposited silver nanoparticles is electrochemically controlled by using a voltage-step method in which two different voltages are applied successively. The electrochemically size-controlled silver nanoparticles enable a reversible multiple-color change by a shift of the LSPR band. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electroswitching of emission and coloration was achieved by a combination of a luminescent Eu(III) complex and an electrochromic molecule of diheptyl viologen (HV2), in order to utilize them as novel display devices with dual emissive-reflective modes. The coloration was associated with the HV2 electrochromism. Emission control was also achieved by the HV2 electrochromism via intermolecular energy transfer from the excited state of the Eu(III) ion to the HV. In order to improve ON-OFF contrast in emission, the emission quantum yield of Eu(III) complex were considerably improved using low vibrational phosphine oxide ligands, resulting in the large control of emission switching. © 2013 The Japan Society of Applied Physics.

Electrochromism is known as an electrochemical reaction exhibiting coloration and can be applied to imaging devices. We successfully prepared a novel indium tin oxide (ITO) electrode modified by electrochromic molecules that displayed a magenta color via electrochemical reduction. The electrochromic molecules of a phthalate derivative were connected to the surface of the ITO electrode by a Si coupling agent. The electrochromic properties of the film were investigated in terms of film thickness and were compared to those of a film using a TiO2 substrate. The thicker film showed larger absorption change and better memory retention than did the film with a TiO2 substrate. © 2013 The Japan Society of Applied Physics.

An AC-driven light-emitting cell based on the electrochemiluminescence (ECL) of tris(2,20-bipyridyl)ruthenium(II) [Ru(bpy)3 2] was fabricated by simply placing the electrolyte solution between transparent electrodes, and this AC-driven ECL cell was demonstrated for comparison to a DC-ECL cell. The properties of the ECL cell were dramatically improved by using the AC method. The AC-ECL cell showed the luminance of 56.4 cd/m2, the current efficiency of 0.78 cd/A and the turn-on response time of ca. 15 ms under application of 4 V, 50Hz AC. We also elucidated the detailed mechanisms of the AC-ECL reaction to monitor the faradaic current. These improved properties and the frequency dependence of the AC-ECL cell were discussed in the relation to the revealed mechanisms. © 2013 The Japan Society of Applied Physics.

Color-tuning of electrochemiluminescence (ECL) emission by frequency modulation of the alternating-current (AC) applied to a single ECL cell containing two different luminescent molecules is demonstrated. Yellow light emission is observed for 1000 Hz AC, while white light is emitted when the frequency is switched to 300 Hz (figure). The ECL cells are simply fabricated by sandwiching an electrolyte solution between transparent electrodes. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A novel method for tuning the color of electrochemiluminescence (ECL) is investigated by N. Kobayashi and co-workers. The emission color from a single AC-driven ECL cell containing two different luminescent molecules is tuned by modulating the applied frequency. As shown on page 144, yellow emission is observed from an ECL cell to which AC is applied at 900-1800 Hz, whereas the emission becomes white when the frequency is adjusted below 800 Hz. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A multifunctional composite film that exhibited thermoresponsive absorption and emission was fabricated using a thermochromic fluoran dye, its developer, and a luminescent europium(iii) complex. The emissions from and coloration of this composite film could be reversibly changed and maintained via the thermochromic reaction taking place within the fluoran dye-developer system. The coloration and decoloration of the composite film were caused by thermoresponsive control of the nanoscale aggregation of structures of the fluoran dye and its developer, whose molecular structure consisted of a long alkyl chain. The control of the phenomenon of photoluminescence could also be achieved via thermochromism, which was induced by intermolecular energy transfer from the Eu(iii) ions in the excited state to the fluoran dye. © 2013 The Royal Society of Chemistry.

A multifunctional composite film that exhibited thermoresponsive absorption and emission was fabricated using a thermochromic fluoran dye, its developer, and a luminescent europium(III) complex. The emissions from and coloration of this composite film could be reversibly changed and maintained via the thermochromic reaction taking place with in the fluoran dye-developer system. The coloration and decoloration of the composite film were caused by thermoresponsive control of the nanoscale aggregation of structures of the fluoran dye and its developer, whose molecular structure consisted of a long alkyl chain. The control of the phenomenon of photoluminescence could also be achieved via thermochromism, which was induced by intermolecular energy transfer from the Eu(III) ions in the excited state to the fluoran dye.