陸川 政弘

Ultra-thin films of the two-dimensional layered perovskites [NH3(CH2)(12)NH3]PbX4 (X = Br, I) with the quantum confinement effect have been fabricated by a convenient self-assembly method.

A new type of organic-inorganic semiconductor heterostructure has been successfully fabricated by incorporating a polydiacetylene backbone into layered perovskite compounds by solid-state polymerization.

The time-resolved photoluminescence spectrum of a polythiophene derivative has been analyzed from the viewpoint of the vibronic structure and its dynamics. We found that the photoluminescence (PL) originates from two vibronic coupled states which consist of the odd-parity 1B(u) component and the even-parity 2A(g) component. Since the fluorescences from the two states have different time constants and different vibronic structures, the PL shows a biexponential decay and a spectral change.

A novel organic-inorganic hybrid compound, C10H10N2PbBr4, was prepared by reacting lead bromide (II) with 4,4'-bipyridinium dibromide, The result of single crystal X-ray analysis indicated that the crystal has one-dimensional chains of line-sharing PbBr6 octahedra. The absorption and fluorescence spectra of the crystals also indicate the formation of one-dimensional inorganic chains and the quantum confinement effect.

Quasi-solid state photovoltaic cells based on high hole mobility conducting polymers, head-to-tail poly(3-alkylthiophene)s (alkyl = butyl, hexyl, dodecyl, and octadecyl) and TiO2 with polymer gel electrolyte have been studied. For the case of using poly(3-butylthiophene) as the sensitizer, the largest photogenerated short-circuit current, open-circuit voltage and fill factor under the light irradiation at 10900 lx are obtained to be 39 muA cm(-2) 0.51V, and 0.68, respectively. The photo-electrical conversion efficiency of the cell is found to increase drastically with decreasing the alkyl chain length.

Photocarrier transport in soluble poly(3-alkylthiophenes)(PATs) has been studied by means of time of flight method. Temperature and field dependencies of mobility were measured for a number of polythiophene derivatives having various alkyl chain lengths from butyl to octadecyl. It has been found that regioregularity has a marked effect on hole mobility in PATs with shorter alkyl group. The results of the mobility in PAT films are discussed in terms of main chain regularity and,alkyl chain lengths.

Photocarrier mobility in Regioregular Poly(3-butylthiophene, P3BT) has been measured in ITO/P3BT/Al sandwich cell configuration using Time-of-Flight technique. Analysis of transient photocurrent suggests the hole as a majority photocarrier. Field and temperature dependence of mobility is presented. Mobility has been found to be unaffected by the thickness and shows a negative field dependence in field < 1 X 10(5) V/cm. We have obtained a room temperature hole mobility of 1.4 X 10(-2) cm(2)/V.s at an applied field of 3 X 10(3) V/cm.

We synthesized an optically active and regioregular poly(3-substituted thiophene), head-to-tail poly(3-[2-(S)-2-methylbutoxy)ethyl]thiophene (HT-P(S)MBET), according to a modified Rieke method. The NT-P(S)MBET was an optically active polymer with the head-to-tail linkage of 94 %. HT-P(S)MBET films showed longer maximum absorption wavelengths and lower bandgap than those of regiorandom poly(3-hexylthiophene). Organic light-emitting diodes (OLED) devices of HT-P(S)MBET showed red electroluminescence with a maximum wavelength of 697 nm.

The carrier transport was investigated depending upon the processes of film preparation in regioregular poly(3-alkylthiophene)s (PATs). The relatively non-dispersive characteristics of photocarrier transport were obtained in drop-cast film. In spin-coated film the transient photocurrent was strong dispersive in contrast. The dispersivity was also slightly increased with the alkyl chain length. The X-ray profiles showed the large crystallinity and the absorption spectra showed the red-shift of peaks in drop-cast film. These results indicate that the dispersivity of carrier transport in PATs is strongly affected by the casting processes of PAT film.

Charge carrier transport in regioregular poly(3-octadecylthiophene) has been studied by the time-of-flight method. The nature of transient photocurrent response is dispersive and holes were found to be the majority photocarriers with no detectable signal for electron transport. The hole mobility at room temperature and at an applied field of $1.3 \times 10^{5}$ V/cm has been measured to be $2.5 \times 10^{-5}$ cm2/V.s. Analysis of the transport mechanism confirms the predictions of the stochastic model of Scher and Montroll as indicated by the universal-scaling behavior of transient photocurrents when they were normalized with respect to transit time. The field and temperature dependence of hole mobility has been analyzed in terms of Poole-Frenkel and Bässler's Gaussian disorder model. The interpretation of the results of hole mobility measurement is made in terms of the concept of hopping among the polymer segments featuring a Gaussian distribution of energies with its variance of 74 meV.

Styrene (St) was polymerized in mixed solvents of ethanol/n-hexane as good-poor solvents for matrix polymers such as poly(methylvinylether) (PMVE) in solution. Conformational change of the matrix polymer from extended to random coil structures provided different dimensional fields for in-situ polymerization of St, resulting in control of particle size and distribution of poly(St) (PSt). Neutron scattering of St solution suggested the formation of St monomer clusters in matrix polymer solution.

Transport properties in regioregular poly(3-alkylthiophene) (PAT) films (alkyl = butyl, hexyl, decyl, dodecyl and octadecyl) have been studied by the time-of-flight (TOF) method for the sandwich cell of indium tin oxide (ITO)/film (spin-coated)/Al. It is found that the photocarriers are the holes, and their mobilities decrease and activation energies increase with increasing alkyl chain length. Poly(3-butylthiophene) exhibits the largest mobility of 1.8 x 10(-2) cm(2/)V s at a field (E) of around 10 kV/cm. The mobility of poly(3-octadecylthiophene) with a value of 1.0 x 10(-6) cm(2)/V s at E = 0.2 mV/cm shows slightly different behavior in field dependence. The TOF mobilities at low field regions show negative field dependence apparently. The negative field dependence of mobilities is explained by proposing a model of heterogeneous field distribution for the Schottky-type cell. The field dependences of the mobilities in regioregular PAT are discussed, comparing them with the results of regiorandom PAT films. (c) 2001 Elsevier Science B.V. All rights reserved.

This paper presents an overview of the synthesis, chemical and electrochemical properties, and polymer electrolyte fuel cell applications of new proton-conducting polymer electrolyte membranes based on hydrocarbon polymers. Due to their chemical stability, high degree of proton conductivity, and remarkable mechanical properties, perfluorinated polymer electrolytes such as Nafion(R), Aciplex(R), Flemion(R), and Dow membranes are some of the most promising electrolyte membranes for polymer electrolyte fuel cells. A number of reviews on the synthesis, electrochemical properties, and fuel cell applications of perfluorinated polymer electrolytes have also appeared during this period. While perfluorinated polymer electrolytes have satisfactory properties for a successful fuel cell electrolyte membrane, the major drawbacks to large-scale commercial use involve cost and low proton-conductivities at high temperatures and low humidities. Presently, one of the most promising ways to obtain high performance proton-conducting polymer electrolyte membranes is the use of hydrocarbon polymers for the polymer backbone. The present review attempts for the first time to summarize the synthesis, chemical and electrochemical properties, and fuel cell applications of new proton-conducting polymer electrolytes based on hydrocarbon polymers that have been made during the past decade. (C) 2000 Elsevier Science Ltd. All rights reserved.

A novel proton-conducting polymer, sulfopropylated poly(benzimidazole) (PBI-PS), was synthesized by the ring-opening reaction of 1,3-propanesultone onto the reactive N-H groups of PBI. The equilibrium water uptake of PBI-PS films increased with increases in the relative humidity and sulfoalkylation level, and the maximum value of water uptake reached 11.3 H2O pel sulfonic acid group (H2O/SO3H) at 90% R.H. and room temperature. The hydrous PBI-PS films showed a high proton conductivity of the order of 10(-3) S cm(-1) in the temperature range from 20 degreesC to 140 degreesC, which is superior to that of conventional proton-conducting polymers. (C) 2000 Elsevier Science B.V. All rights reserved.

We measured the time-resolved photoluminescence of highly ordered and disordered films of a polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene). The formation of self-trapped excitons (STE's) within 10 ps after photoexcitation and the subsequent migration of the STE's are common behavior in both films. The spectral narrowing of the phonon sidebands within 10 ps after photoexcitation is associated with the formation process of STE's and the spectral changes on a few hundred ps time scale are explained by the STE migration and the dependence of the electron-phonon coupling on the effective conjugation length.

A novel proton-conducting polymer, sulfopropylated poly(benzimidazole) (PBI-PS), was synthesized by the ring-opening reaction of I,3-propanesultone on the reactive N-H groups of PBI. Cast pms of PBI-PS obtained from a dimethylsulfoxide solution of PBI-PS exhibited high water uptake, adequate mechanical strength, and flexibility. The temperature dependence of proton conductivity for PBI-PS films hydrated at 90% R.H. showed high proton conductivity of the order of 10(-3) Scm(-1) in the temperature range from room temperature to 140 degreesC, which is superior to those of conventional proton conducting polymers such as Nafion. The physical behavior of absorbed water in hydrous PBI-PS pms was evaluated by differential scanning calorimetry (DSC), indicating that the absorbed water in PBI-PS mainly consisted of freezing bound water. Copyright (C) 2000 John Wiley & Sons, Ltd.

Carrier mobilities in poly(3-alkylthiphene) cast films have been studied by means of fabricating a field effect transistor (FET) at the field range of (0.3-1.6)x 10(4) V/cm. It is found that the regioregurality is markedly effective to the mobilities than the side chain length. The FET mobility of the regioregular poly(3-hexylthiophene), PHT is approximately 3x10(-3) cm(2)/Vs which is larger than that of regiorandom PhT by 3 orders of magnitude. The mobility of regioregular poly(3-dodecylthiophene), PDDT is 8 x10(-4) cm(2)/Vs and is also 3 orders of magnitude larger than that of regiorandom PDDT. The mobilities of regioregular ones decrease, however, those of regiorandom ones increase at higher fields. Time FET mobilities are nearly same to the mobilities estimated by the time of flight method. These results have been discussed taking the regularity of the main chain and the length of side chain into consideration.

Thin films of layered perovskite compounds (CnH2n+1NH3)(2)(CH3NH3)(m-1)PbmBr3m+1 (m = 1, 2 and 3) were prepared by the spin-coating method from their DMF (N,N-dimethylformamide) solutions. The control of the inorganic layer thickness in layered perovskites can be achieved by changing the ratio of the two amines (CnH2n+1NH3/CH3NH3) The layered perovskite films showed a strong, clear exciton absorption peak at room temperature due to their large exciton binding energy. With increasing numbers of inorganic layers, a red shift of the exciton absorption was observed due to the decrease in transfer energy. X-ray diffraction patterns clearly demonstrated that the spin-coated film was highly oriented normal to the surface, which is consistent with 'mono', 'bi', and 'tri' layer structures, respectively. The effect of the alkyl chain length of the organic part was also investigated. (C) 2000 Elsevier Science Ltd. All rights reserved.

We measured the absorption and \chi((3))\ spectra around the excitonic resonance for Langmuir-Blodgett (LB) film of polythiophene derivative, poly(3-[2((S)-2-methylbutoxy)ethyl]thiophene) at 10 K and room temperature. We derived a theoretical distribution function for the effective conjugation length taking the molecular weight distribution into consideration, and fitted the calculated absorption and \chi((3))\ spectra to the experimental ones. From the fits, we estimated the average effective conjugation length to be 21 thiophene rings at 10 K, and 15 thiophene rings at room temperature.

The time-of-night technique has been used to study transports of photocarriers in regioregular and regiorandom poly(3-hexylthiophene) (P3HT) films by fabricating indium-tin-oxide/P3HT/Al sandwich cell. It has been found that regularity in the coupling of monomers, head-to-tail (HT) has a marked effect on electrical properties and photocarrier transport in P3HT. Both regular and random P3HT films exhibit a dispersive photocurrent response with the positive sign of photocarrier (hole). The room temperature hole mobility of regioregular P3HT is estimated to be 1.21 x 10(-3) cm(2)/V.s and is one order of magnitude larger than that of the random one. The mobility in regioregular P3HT is almost independent of the applied field while that of random P3HT shows a positive field dependence at the field larger than 1.0 x 10(5) V/cm.

We measured time-resolved photoluminescence on highly ordered and disorder films of polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene]. A migration of self-trapped exciton (STE) is observed in both films, and a structural dependence of the STE behavior is revealed. (C)2000 Optical Society of America.

The time resolved photoluminescence experiments on highly ordered films of polythiophene derivative are reported to understand their excitation dynamics. Two films were prepared. One is a Langmuir-Blodgett (LB) film which contains almost 100% head-to-tail coupling of the side chain. Another is a spin coated film where each thiophene ring has the side chain at random position so that the collision of the side chains causes the torsion of thiophene rings. The high energy tail of luminescence is considered to arise from hot self trap excitons and that the slow red shift is caused by the migration of the self trap exciton to lower energy sites.

We synthesized thermally stable proton-conducting polymers composed of poly(benzimidazole) (PBI) and strong acids. PBI films were doped with strong acids such as phosphoric, sulfuric, and hydrochloric acid by immersing them into a mixed solution of strong acid and methanol. We found that the PBI films and strong acids formed polymer complexes because they showed the acid-base or the hydrogen bonding interactions between imidazole groups of PBI and acid molecules. The PBI/H3PO4 complexes were thermally stable up to 500 degrees C, and the proton conductivity of anhydrous complexes reached 10(-5) S cm(-1) at 160 degrees C. (C) 2000 Elsevier Science Ltd. All rights reserved.

New polymer/ligand complexes could be easily obtained due to the molecular self-assembly of carboxylic acid and hydrogen acceptor fragments through the intermolecular hydrogen-bonding. The polymer/ligand complexes consisting of poly(ethyleneglycol)bis(carboxymethyl)ether (PEO-CA), operating as a hydrogen-bonding donor, and pyrazine, 4,4'-bipyridine, or 1,3,5-triazine, serving as a hydrogen-bonding acceptor, exhibited a gel-like structure at room temperature. The high ion conductivity of the order of 10(-4)-10(-6) S cm(-1) was achieved for the PEO-CA/ligand complexes with LiClO4. The decrease in their conductivity corresponded to the increase in the viscosity and glass transition temperatures of the polymer complexes, but their electrical properties were similar to those of conventional cross-linked PEO polymer electrolytes. (C) 2000 Elsevier Science Ltd. All rights reserved.

New proton conducting polymers based on poly(silamine) (PSA) were synthesized by complexing the polymer and H3PO4, and the proton conduction of these materials was investigated. The PSA/H3PO4 complex was thermally stable up to 200 degrees C, as indicated by TG/DTA analysis. The conductivity of 10(-5) S cm(-1) was observed at 160 degrees C for anhydrous PSA/H3PO4 complexes with a concentration of 0.8 H3PO4 per repeat unit. The carrier ion was proven to be proton on the basis of the H/D isotope effect on conductivity for PSA/H3PO4 and PSA/D3PO4 complexes. (C) 2000 Elsevier Science Ltd. All rights reserved.

We measured the spectra of the third-order optical nonlinearity, |χ(3)(ω;ω,ω,-ω)| around excitonic resonance in spincoated films and Langmuir-Blodgett (LB) films of polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene), using the degenerate four wave mixing method. The value of |χ(3)(ω;ω,ω,-ω)| at the exciton resonance was approximately 10-7 esu, which was the largest value ever obtained in conjugated polymers.

The carrier mobility in the regioregular poly(3-hexylthiophene)(PHT) film has been studied by means of the time of flight (TOF) method using a sandwich-type cell of indium tin oxide(ITO)/PHT (cast film)/Al. The response of the photocurrent exhibits a dispersive character, however, the clear kink associated with the transit time of the carder is observed. The drift mobility of holes is determined to be 4 x 10(-4) cm(2)/V-s and almost independent of the field > 10(5) V/cm at room temperature, This is the largest TOF mobility in poly(3-alkylthiophene) reported to date. It is also found that the activation energy of the mobility is 88 meV and almost independent of the field. The results are discussed taking various transport models into consideration.

Molecular alignments of poly(3-alkylthiophene)s deposited on the Au(111) facet are studied by scanning tunneling microscopy (STM). In regioregular poly(3-hexylthiophene) and poly(3-dodecylthiophene), the individual polymer is clearly imaged as a silkworm. On the other band, regiorandom poly(3-octadecylthiophene) does not show any distinguishable image of the individual polymer. The molecular shapes and the preparation method of the structurally aligned regioregular poly(3-alkylthiophene)s are described.

Super-fine particles of sub-micron sizes of poly(styrene-co-methyl methacrylate) were synthesized by dispersion copolymerization in an ethanol-hexane mixture in the presence of a matrix polymer of poly(methyl vinyl ether). The effects of the matrix polymer, monomer feed ratio, ethanol-to-hexane ratio, and polymerization temperature were investigated for particle size and size distribution by SEM, molecular weights, and polydispersity index by GPC. Solubility of the matrix polymer in the medium to provide excluded free volumes in the polymer solution is plausibly the main attribute of controlling the morphology of the matrix polymer that directly affects the particle size and distribution in addition to its steric barrier effect. Particles with a spherical shape of 1-5 mu m were formed. The average molecular weights became larger in smaller particles. The copolymers in bulk and solution (without PMVE) were aggregated into a big lump. Increasing the styrene feed decreased the particle sizes with a narrow size distribution. Increasing the ethanol-to-hexane ratio decreased the copolymer particle sizes. The polymerization temperature range for the copolymerization was 50-64 degrees C. The reaction did not occur when polymerizing at 40 degrees C and the agglomerated particles were produced at a 73 degrees C reaction temperature. This article describes the effects of each parameter on the particle size and distribution. Solution and bulk copolymerizations were also carried out to compare the particle size and composition of the copolymer. (C) 1999 Elsevier Science B.V. All rights reserved.

Buckminsterfullerene (C-60)molecules have been known to form organic charge transfer ( CT) complexes with electron-donor compounds. In this study, we have prepared the complexes of fullerene and 2,3,9,10,16,17,23,24-octakis{(octyloxy)-phthalocyaninato}metal (MPc(OC8H17)(8), M=2H, Cu, Zn) by using the Langmuir-Blodgett ( LB) technique on the air-water interface for investigating the interaction between C-60 and MPc(OC8H17)(8). Monolayers of mixtures of C-60 and MPc(OC8H17)(8) were prepared by spreading a benzene solution of C-60 and MPc(OC8H17)(8) on the air-water interface at 10 degrees C. The monolayers were transferred by the horizontal lifting method These multilayer films were characterized by UV-Vis, polarized UV-Vis and X-ray diffraction measurements.

Langmuir-Blodgett films have been fabricated from a regioregular poly(thiophene) derivative by the vertical dipping method while still maintaining the high self-organization associated with the regioregularity of the polymer.

We fabricated electrostatic self-assembled thin films with poly(thiophene-3-acetic acid) (PTAA) as a polyanion and a positively-charged second-order NLO chromophore as a cation. UV-Vis, FT-IR, and second-harmonic generation (SHG) were measured in order to investigate the process of anion and carion adsorption and to understand the relationship between structure and optical properties of the ultra thin films. UV-Vis and FT-IR spectra of these films indicated that PTAA and the NLO chromophore formed a layer-by-layer structure. SHG measurements suggested that the NLO chromophores were non-centrosymmetrically aligned within the self-assembled films.

Chiral Langmuir-Blodgett (LR) films were fabricated from mixed monolayers containing regioregular poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene) (HT-P(S)MBET) and stearic acid (SA) with different molar ratios. The NT-P(S)MBET was an optically active polymer with the head-to-tail linkage of larger than 93 %. From the W-Vis spectra and X-ray diffraction measurements, it was found that the ITT-P(S)MBET in the LR film form a layered structure in which the main chains are oriented parallel to the plane of the substrate and exhibit a tendency to orient along the dipping direction. The in-plane conductivity of the HT-P(S)MBET SA LB film doped with SbCl5, was 1.2 S cm(-1) The observed value of the third-order nonlinear susceptibility at the exciton resonance peak was in the order of 10(-7) - 10(-8) esu.

The spectra of the third-order optical nonlinearity, \chi((3))(omega;omega,omega,-omega)\, around excitonic resonance in a spin-coated film and a Langmuir-Blodgett (LB) film of polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene), were measured using the degenerate four-wave-mixing method. The obtained value of \chi((3))(omega;omega,omega,-omega)\ at the excitonic resonance was similar to 10(-7) esu, which was the largest value ever obtained in conjugated polymers. From the absorption spectra and \chi((3))\ spectra, the average effective conjugation lengths of the spin-coated film and the LB film were estimated to be approximately 20- and 36-thiophene rings, respectively. [S0163-1829(98)50144-0].

We synthesized an optically active regioregular poly(3-substituted thiophene), head-to-tail poly(3-[2-((S)-2-methylbutoxy)ethyl] thiophene) (HT-P(S)MBET), according to a modified Rieke method. The HT-P(S)MBET was an optically active polymer with the HT linkage of larger than 93%, as estimated by NMR. The mixed monolayers of the polymer and stearic acid (SA) were found to be stable at the air-water interface and could be deposited onto solid substrates as Y-type films by the vertical dipping method. These Langmuir-Blodgett (LB) films exhibited well-defined layer structures and unique optical properties. The electrical conductivities of the LB films with and without doping of SbCl5 were about 10(-1) and 10(-5) S/cm, respectively. (C) 1998 Elsevier Science S.A. All rights reserved.